














                           NYQUIST REFERENCE MANUAL

                                 Version 2.36


                     Copyright 2007 by Roger B. Dannenberg
                                 5 March 2007











                          Carnegie Mellon University

                          School of Computer Science

                         Pittsburgh, PA 15213, U.S.A.
  .
Preface
  This  manual  is a guide for users of Nyquist, a language for composition and
sound synthesis.  Nyquist grew out of a series of  research  projects,  notably
the  languages Arctic and Canon.  Along with Nyquist, these languages promote a
functional  style  of  programming  and  incorporate  time  into  the  language
semantics.

  Please  help  by  noting  any errors, omissions, or suggestions you may have.
You can send your suggestions to Dannenberg@CS.CMU.EDU (internet) via  computer
mail,  or by campus mail to Roger B. Dannenberg, School of Computer Science, or
by ordinary mail to Roger B. Dannenberg, School of Computer  Science,  Carnegie
Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213-3890, USA.

  Nyquist  is  a successor to Fugue, a language originally implemented by Chris
Fraley, and extended by George Polly and Roger Dannenberg.  Peter Velikonja and
Dean  Rubine  were early users, and they proved the value as well as discovered
some early problems of the system.  This led to Nyquist, a reimplementation  of
Fugue by Roger Dannenberg with help from Joe Newcomer and Cliff Mercer. Ning Hu
ported Zheng (Geoffrey) Hua and Jim Beauchamp's piano  synthesizer  to  Nyquist
and  also  built  NyqIDE,  the  Nyquist Interactive Development Environment for
Windows.  Dave  Mowatt  contributed  the  original  version  of  jNyqIDE,   the
cross-platform  interactive  development  environment.   Dominic Mazzoni made a
special version of Nyquist that runs within the Audacity audio  editor,  giving
Nyquist a new interface and introducing Nyquist to many new users.

  Many  others have since contributed to Nyquist.  Chris Tchou and Morgan Green
worked on the Windows port. Eli Brandt contributed  a  number  of  filters  and
other  synthesis  functions. Pedro J. Morales, Eduardo Reck Miranda, Ann Lewis,
and Erich Neuwirth have all contributed nyquist examples  found  in  the  demos
folder of the Nyquist distribution.  Philip Yam ported some synthesis functions
from Perry Cook and Gary Scavone's STK to Nyquist.  Dave Borel wrote the  Dolby
Pro-Logic  encoding  library  and  Adam Hartman wrote stereo and spatialization
effects. Stephen Mangiat wrote  the  MiniMoog  emulator.  The  Xmusic  library,
particularly  the  pattern  specification,  was inspired by Rick Taube's Common
Music. The functions for generating probability distributions were  implemented
by Andreas Pfenning.

  Many others have made contributions, offered suggestions, and found bugs.  If
you were expecting to find your name here, I apologize for  the  omission,  and
please let me know.

  I also wish to acknowledge support from CMU, Yamaha, and IBM for this work.






























.
1. Introduction and Overview
  Nyquist  is  a  language  for  sound synthesis and music composition.  Unlike
score languages that tend to  deal  only  with  events,  or  signal  processing
languages  that  tend  to deal only with signals and synthesis, Nyquist handles
both in a single integrated system.  Nyquist is also flexible and easy  to  use
because it is based on an interactive Lisp interpreter.

  With  Nyquist, you can design instruments by combining functions (much as you
would using the orchestra languages of Music V, cmusic, or Csound).    You  can
call  upon  these  instruments  and  generate  a  sound just by typing a simple
expression.  You can combine simple expressions into complex ones to  create  a
whole composition.

  Nyquist  runs  under any Unix environment, MacOS, Windows 95, and Windows NT,
and it produces sound files as output (or direct audio output  under  Windows).
Under  Unix,  if you can play a sound file by typing a command to a Unix shell,
then you can get Nyquist  to  play  sounds  for  you.    Nyquist  is  currently
configured to run on an IBM RS6000 with an ACPA audio board, or a NeXT machine,
using the built-in sound system to play Nyquist output.  Recent  versions  have
also  run  on  SGI,  DEC pmax, Linux, and Sun Sparc machines, and makefiles for
these are included.  Let me know  if  you  have  problems  with  any  of  these
machines.

  To use Nyquist, you should have a basic knowledge of Lisp.  An excellent text
by Touretzky is recommended [Touretzky 84].    Appendix  IV  is  the  reference
manual for XLISP, of which Nyquist is a superset.

1.1. Installation
  Nyquist  is  a  C  program  intended  to  run under various operating systems
including Unix, MacOS, and Windows.



1.1.1. Unix Installation
  For Unix systems, Nyquist is distributed  as  a  compressed  tar  file  named
nyquist2nn.zip, where nn is the version number (e.g. v2.19 was nyquist219.zip).
To install Nyquist, copy nyquist2nn.zip to a fresh directory  on  your  machine
and type:

    gunzip nyquist2nn.zip
    ln -s sys/unix/linux/Makefile Makefile
    setenv XLISPPATH `pwd`/runtime:`pwd`/lib
    make

The  first line creates a nyquist directory and some subdirectories. The second
line makes a link from the top-level directory to the Makefile for your system.
In place of linux in sys/unix/linux/Makefile, you should substitute your system
type. Current systems are next, pmax, rs6k, sgi, linux, and sparc.  The  setenv
command  tells  Nyquist where to search for lisp files to be loaded when a file
is not found in the current directory. The runtime directory should  always  be
on  your  XLISPPATH  when  you run Nyquist, so you may want to set XLISPPATH in
your  shell  startup  file,  e.g.    .cshrc.    Assuming  the  make   completes
successfully, you can run Nyquist as follows:

    ./ny

When  you  get the prompt, you may begin typing expressions such as the ones in
the following ``Examples'' section.

  One you establish that Nyquist (ny) is working from  the  command  line,  you
should  try  using  jNyqIDE,  the  Java-based  Nyquist development environment.
First, make jny executable (do this only once when you install Nyquist):

    chmod +x jny

Then try running jNyqIDE by typing:

    ./jny

If the jNyqIDE window does not appear, make sure you have  Java  installed  (if
not,  you  probably already encountered errors when you ran make). You can also
try recompiling the Java files:

    cd jnyqide
    javac *.java
    cd ..

  Note: With Linux and the Macintosh OS  X,  jNyqIDE  defines  the  environment
passed  to  Nyquist.  If  you  set XLISPPATH as shown above, it will be ignored
under jNyqIDE. Instead, the XLISPPATH will have the lib and runtime directories
only.    This  does not apply to Windows because even though the environment is
there, the Windows version of Nyquist reads the XLISPPATH from the Registry.

  You can specify additional directories for the search path  by  creating  the
file  nyquist/xlisppath,  which  should  have colon-separated paths on a single
line of text.

  Note: Nyquist looks for the file init.lsp in the current directory.   If  you
look  in  the init.lsp in runtime, you will notice two things.  First, init.lsp
loads nyquist.lsp from  the  Nyquist  directory,  and  second,  init.lsp  loads
system.lsp  which  in  turn  defines  the  macro  play.  You may have to modify
system.lsp to invoke the right programs on your machine.



1.1.2. Win32 Installation
  The Win32 version of Nyquist  is  packaged  in  three  versions:  the  source
version  and  two  runtime  versions.  The  source version is a superset of the
runtime version intended for developers who  want  to  recompile  Nyquist.  The
source  version  exists  as  a  .zip file, so you need a utility like WinZip to
unpack them.  The URL http://www.winzip.com/ has information on  this  product.
Typically,  the  contents  of  the  zip  file  are  extracted to the C:\nyquist
directory, but you can put  it  anywhere  you  like.  You  can  then  open  the
workspace  file, nyquist.dsw, using Microsoft Visual C++. You can build and run
the command line and the NyqWin versions of Nyquist from within Visual C++.

  The runtime versions contain everything you need to  run  Nyquist,  including
the  executable,  examples, and documentation. Each runtime version is packaged
as an executable installer program.  I recommend setupnyqiderun2xx.exe (``2xx''
refers  to  the  current version number), a graphical interface written in Java
that runs nyquist.exe as a separate process. This IDE has a simple lisp  editor
built  in.  Alternatively,  you  can install setupnyqwinrun2xx.exe, a different
graphical interface written in C++. Just copy the installer you  want  to  your
system  and  run  it.  Then find Nyquist in your Start menu to run it.  You may
begin typing expressions  such  as  the  ones  in  the  following  ``Examples''
section.

  Optional: Nyquist needs to know where to find the standard runtime files. The
location of runtime files must be stored  in  the  Registry.    The  installers
create  a  registry  entry,  but  if  you  move  Nyquist or deal with different
versions, you can edit the Registry manually as follows:

   - Run    the    Registry    editor.    Under    Windows     NT,     run
     C:\WINNT\system32\regedt32.exe.       Under       Windows95,      run
     C:\WINDOWS\regedit.exe.

   - Find and highlight the SOFTWARE key under HKEY_LOCAL_MACHINE.

   - Choose Add key ... from the Edit menu, type CMU,  and  click  the  OK
     button.

   - Highlight the new CMU key.

   - Choose Add key ... from the Edit menu, type Nyquist, and click the OK
     button.  (Note that CMU and Nyquist are case sensitive.)

   - Highlight the new Nyquist key.

   - Choose Add value ... from the Edit menu, type  XLISPPATH,  and  click
     the  OK button.  (Under WinXP the menu item is Edit:New:String Value,
     after which you need to select the new string name  that  appears  in
     the right panel, select Edit:Rename, and type XLISPPATH.)

   - In  the  String Edit box (select the Edit:Modify menu item in WinXP),
     type a list of paths you want Nyquist to search for lisp  files.  For
     example, if you installed Nyquist as C:\nyquist, then type:

         C:\nyquist\runtime,C:\nyquist\lib

     The  paths  should be separated by a comma or semicolon and no space.
     The runtime path is essential, and the lib path may become  essential
     in  a future release. You can also add paths to personal libraries of
     Lisp and Nyquist code.

   - Click the OK button of the string box  and  exit  from  the  Registry
     Editor application.


1.1.2.1. What if Nyquist functions are undefined?
  If  you do not have administrative privileges for your machine, the installer
may fail to set up the Registry entry that Nyquist uses to find  initialization
files.  In  this  case,  Nyquist  will run a lisp interpreter, but many Nyquist
functions will not be defined. If you can log in as administrator,  do  it  and
reinstall  Nyquist. If you do not have permission, you can still run Nyquist as
follows:

  Create a file named init.lsp  in  the  same  directory  as  Nyquist.exe  (the
default  location is C:\Program Files\Nyquist, but you may have installed it in
some other location.) Put the following text in init.lsp:

    (setf *search-path* "C:/Program Files/Nyquist/runtime,C:/Program Files/
    (load "C:/Program Files/Nyquist/runtime/init.lsp")

Note: in the three places where you see C:/Program  Files/Nyquist,  insert  the
full  path  where Nyquist is actually installed. Use forward slashes (/) rather
than back slashes (\) to separate  directories.  For  example,  if  Nyquist  is
installed at D:\rbd\nyquist, then init.lsp should contain:

    (setf *search-path* "D:/rbd/nyquist/runtime,D:/rbd/nyquist/lib")
    (load "d:/rbd/nyquist/runtime/init.lsp")

The  variable  *search-path*,  if  defined, is used in place of the registry to
determine search paths for files.


1.1.2.2. SystemRoot
  (Ignore this paragraph if you are not planning  to  use  Open  Sound  Control
under  Windows.)   If Nyquist prints an error message and quits when you enable
Open Sound Control (using osc-enable), check to see if you have an  environment
variable  SystemRoot,  e.g. type set to a command prompt and look for the value
of SystemRoot. The normal value is C:\windows. If the value is something  else,
you should put the environment entry, for example:

    SystemRoot="D:\windows"

into  a  file  named  systemroot  (no extension). Put this file in your nyquist
directory. When you run jNyqIDE, it will  look  for  this  file  and  pass  the
contents  as an environment variable to Nyquist. The Nyquist process needs this
to open a UDP socket, which is needed for Open Sound Control.
1.1.3. MacOS 9 Installation
  The MacOS 9 version of Nyquist is no longer  supported,  but  a  old  version
still  exists.    The MacOS version of Nyquist is packaged in two versions: the
source version and the runtime version.  The source version is  a  superset  of
the  runtime  version. Both exist as self extracting archives, so you just need
to copy the archive file of your choice to your machine and double click on its
icon.  You can extract the archive to any folder you like.

  You  will  find  Nyquist  in  the  runtime folder. Double click on it and you
should see a text window with some information that Nyquist has started and has
loaded  some  files.   You may begin typing expressions such as the ones in the
following section.

  On    the    Macintosh,    Nyquist    automatically    creates     a     file
"System:Preferences:XLisp  Preferences"  with  a default search path for files.
You can edit this file to add  new  locations,  although  this  should  not  be
necessary for most uses.



1.1.4. MacOS X Installation
  The  OS  X version of Nyquist is very similar to the Linux version, but it is
developed using Xcode, Apple's programming environment. With a little work, you
can use the Linux installation instructions to compile Nyquist, but it might be
simpler to just open the Xcode project that is included in the Nyquist sources.

  You can also download a pre-compiled version of Nyquist for the  Mac.    Just
download  nyqosx2xx.tgz  to  the  desktop  and  open  it  to extract the folder
<tt>nyqosx2xx</tt>. (Again, "2xx" refers to the current  version  number,  e.g.
v2.31  would  be  named  with "231".) Open the folder to find a Mac Application
named jNyqIDE and a directory named <tt>nyquist/doc</tt>. Documentation  is  in
the <tt>nyquist/doc</tt> directory.

  The  file <tt>jNyqIDE.app/Contents/Resources/Java/ny</tt> is the command line
executable (if you should need it). To run from the command line, you will need
to  set  the  XLISPPATH environment variable as with Linux. On the topic of the
XLISPPATH, note that this variable is set by jNyqIDE  when  running  with  that
application,  overriding  any  other  value.  You can extend the search path by
creating the file xlisppath in the same directory as the nyquist executable ny.
The xlisppath file should have colon-separated paths on a single line of text.

1.2. Helpful Hints
  Under  Win95  and  Win98,  the console sometimes locks up. Activating another
window and then reactivating the Nyquist window should unlock the output.   (We
suggest  you use JNyqIDE, the interactive development environment rather than a
console window.)

  You can cut and paste text into Nyquist, but for serious work, you will  want
to  use the Lisp load command. To save even more time, write a function to load
your working file, e.g. (defun l () (load "myfile.lsp")). Then you can type (l)
to (re)load your file.

  Under  Windows,  if  you encounter an error while loading a file, the file is
left open, and you may not be able to overwrite the file with a correction.  To
close  the file, type (top) to exit the debugger and resume at the top level of
the interpreter. You may need to type (gc) to force a garbage collection.  This
will  free  and  close  the  file.  Now  you can modify the file with your text
editor.

  The Emacs editor is free GNU software and will help you  balance  parentheses
if  you use Lisp mode. Also, the NyqIDE and jNyqIDE versions have built-in lisp
editors. If your editor does not help you balance  parentheses,  you  may  find
yourself  counting  parens and searching for unbalanced expressions. If you are
desparate, type (file-sexprs) and type the lisp file name at the  prompt.  This
function will read and print expressions from the file, reporting an error when
an extra paren or end-of-file is reached unexpectedly. By looking at  the  last
expression  printed,  you  can  at  least  tell where the unbalanced expression
starts. Alternatively, try the verbose mode of the load command.

1.3. Examples
  We will begin with some simple Nyquist programs.   Detailed  explanations  of
the functions used in these examples will be presented in later chapters, so at
this point, you should just read these examples to get a sense of  how  Nyquist
is  used  and  what  it  can  do.   The details will come later.  Most of these
examples can be found in the file nyquist/sndtest/tutorial.lsp.

  Our first example makes and plays a sound:

    ;; Making a sound.
    (play (osc 60))  ; generate a loud sine wave

This example is about the simplest way to create a sound with Nyquist.  The osc
function generates a sound using a table-lookup oscillator.  There are a number
of optional parameters, but the default  is  to  compute  a  sinusoid  with  an
amplitude  of  1.0.    The  parameter 60 designates a pitch of middle C. (Pitch
specification will be described in greater detail later.)  The  result  of  the
osc  function  is  a  sound.   To hear a sound, you must use the play function,
which under Unix writes the sound as a  16-bit  sound  file  and  runs  a  Unix
program  that  plays  the  file  through  the  machine's D/A converters. On the
Macintosh, you have to explicitly play the  file  from  another  program,  e.g.
SoundApp,  which  is  included in the Macintosh release. Under Windows, Nyquist
outputs audio directly. It also writes a  soundfile  in  case  the  computation
cannot keep up with real time. You can then (re)play the file by typing:

    (r)

This  (r)  command is a general command to ``replay'' the last thing written by
play.
                                                                 15
  Note: when Nyquist plays a sound, it scales  the  signal  by  2  -1  and  (by
default)  converts  to  a  16-bit integer format. A signal like (osc 60), which
ranges from +1 to -1, will play as a full-scale 16-bit  audio  signal.  Signals
are  not normalized to full-scale, however, so an amplitude in excess of 1 will
be clipped.  See Section 4.3 for information about normalization.



1.3.1. Waveforms
  Our next example will be presented in several steps.  The goal is to create a
sound  using a wavetable consisting of several harmonics as opposed to a simple
sinusoid.  In order to build a table, we will use a function  that  computes  a
single  harmonic  and add harmonics to form a wavetable.  An oscillator will be
used to compute the harmonics.

  The function mkwave calls upon build-harmonic to generate  a  total  of  four
harmonics  with  amplitudes  1.0, 0.5, 0.25, and 0.12.  These are scaled (using
scale) and added (using sim) to create a waveform which is bound temporarily to
*table*.

  A  complete Nyquist waveform is a list consisting of a sound, a pitch, and T,
indicating a periodic waveform.  The pitch  gives  the  nominal  pitch  of  the
sound.  (This is implicit in a single cycle wave table, but a sampled sound may
have many periods of the fundamental.)  Pitch is expressed in half-steps, where
middle  C is 60 steps, as in MIDI pitch numbers.  The list of sound, pitch, and
T is formed in the last line of mkwave: since build-harmonic  computes  signals
with  a  duration  of  one  second, the fundamental is 1 Hz, and the hz-to-step
function converts to pitch (in units of steps) as required.

    (defun mkwave ()
      (setf *table* (sim (scale 0.5  (build-harmonic 1.0 2048))
                        (scale 0.25  (build-harmonic 2.0 2048))
                        (scale 0.125 (build-harmonic 3.0 2048))
                        (scale 0.062 (build-harmonic 4.0 2048))))
      (setf *table* (list *table* (hz-to-step 1) T)))

  Now that we have defined a function, the last step  of  this  example  is  to
build  the  wave.    The following code calls mkwave the first time the code is
executed (loaded from a file).  The second time, the variable *mkwave* will  be
true, so mkwave will not be invoked:

    (cond ((not (boundp '*mkwave*))
           (mkwave)
           (setf *mkwave* t)))



1.3.2. Wavetables
  When  Nyquist  starts,  several  waveforms  are  created and stored in global
variables  for  convenience.   They   are:   *sine-table*,   *saw-table*,   and
*tri-table*, implementing sinusoid, sawtooth, and triangle waves, respectively.
The variable *table* is initialized to *sine-table*, and  it  is  *table*  that
forms the default wave table for many Nyquist oscillator behaviors. If you want
a proper, band-limited waveform, you should construct it yourself, but  if  you
do  not understand this sentence and/or you do not mind a bit of aliasing, give
*saw-table* and *tri-table* a try.

  Note that in Lisp, global variables often start and end with  asterisks  (*).
These  are  not  special  syntax,  they  just happen to be legal characters for
names, and their use is purely a convention.



1.3.3. Sequences
  Finally, we define note to use the waveform, and  play  several  notes  in  a
simple score:

    (defun note (pitch dur)
      (osc pitch dur *table*))

    (play (seq (note c4 i)
               (note d4 i)
               (note f4 i)
               (note g4 i)
               (note d4 q)))

Here, note is defined to take pitch and duration as parameters; it calls osc to
do the work of generating a waveform, using *table* as a wave table.

  The seq function is used to invoke a sequence of behaviors.    Each  note  is
started  at  the  time  the previous note finishes.  The parameters to note are
predefined in Nyquist: c4 is middle C, i (for eIghth note) is 0.5, and  q  (for
Quarter  note) is 1.0.  See Section 1.4 for a complete description.  The result
is the sum of all the computed sounds.

  Sequences can also be constructed using the at transformation to specify time
offsets.   See   sequence_example.htmdemos,  sequence  for  more  examples  and
explanation.



1.3.4. Envelopes
  The next example will illustrate the use of envelopes.  In Nyquist, envelopes
are  just  ordinary sounds (although they normally have a low sample rate).  An
envelope is applied to another sound by multiplication using the mult function.
The  code  shows  the  definition  of  env-note,  defined  in terms of the note
function in the previous example.  In env-note, a 4-phase envelope is generated
using the env function, which is illustrated in Figure 1.

    ; env-note produces an enveloped note.  The duration
    ;   defaults to 1.0, but stretch can be used to change















     Figure 1:  An envelope generated by the env function.


    ;   the duration.
    ;
    (defun env-note (p)
      (mult (note p 1.0)
            (env 0.05 0.1 0.5 1.0 0.5 0.4)))

    ; try it out:
    ;
    (play (env-note c4))

While  this  example shows a smooth envelope multiplied by an audio signal, you
can also use mult to multiply to audio signals to achieve what is often  called
ring modulation. See the code and description in demos/scratch_tutorial.htm for
an interesting use of ring modulation to create ``scratch'' sounds.

  In the next example, stretch is used to modify durations:

    ; now use stretch to play different durations
    ;
    (play
           (seq (stretch 0.25
                         (seq (env-note c4)
                              (env-note d4)))
                (stretch 0.5
                         (seq (env-note f4)
                              (env-note g4)))
                (env-note c4)))

  In addition to stretch, there are a number of  transformations  supported  by
Nyquist,  and  transformations of abstract behaviors is perhaps the fundamental
idea behind Nyquist.  Chapter 2 is devoted  to  explaining  this  concept,  and
further elaboration can be found elsewhere [Dannenberg 89].



1.3.5. Piece-wise Linear Functions
  It is often convenient to construct signals in Nyquist using a list of (time,
value) breakpoints which are linearly interpolated to  form  a  smooth  signal.
Envelopes  created  by  env  are  a special case of the more general piece-wise
linear functions created by pwl.  Since pwl is used in some examples later  on,
we  will  take  a look at pwl now.  The pwl function takes a list of parameters
which denote (time, value) pairs.  There is an implicit initial  (time,  value)
pair  of  (0,  0), and an implicit final value of 0.  There should always be an
odd number of parameters, since the final time is not implicit.  Here are  some
examples:

    ; symetric rise to 10 (at time 1) and fall back to 0 (at time 2):
    ;
    (pwl 1 10 2)

    ; a square pulse of height 10 and duration 5.
    ; Note that the first pair (0, 10) overrides the default initial
    ; point of (0, 0).  Also, there are two points specified at time 5:
    ; (5, 10) and (5, 0).  (The last 0 is implicit).  The conflict is
    ; automatically resolved by pushing the (5, 10) breakpoint back to
    ; the previous sample, so the actual time will be 5 - 1/sr, where
    ; sr is the sample rate.
    ;
    (pwl 0 10 5 10 5)

    ; a constant function with the value zero over the time interval
    ; 0 to 3.5.  This is a very degenerate form of pwl.  Recall that there
    ; is an implicit initial point at (0, 0) and a final implicit value of
    ; 0, so this is really specifying two breakpoints: (0, 0) and (3.5, 0):
    ;
    (pwl 3.5)

    ; a linear ramp from 0 to 10 and duration 1.
    ; Note the ramp returns to zero at time 1.  As with the square pulse
    ; above, the breakpoint (1, 10) is pushed back to the previous sample.
    ;
    (pwl 1 10 1)

    ; If you really want a linear ramp to reach its final value at the
    ; specified time, you need to make a signal that is one sample longer.
    ; The RAMP function does this:
    ;
    (ramp 10) ; ramp from 0 to 10 with duration 1 + one sample period
    ;
    ; RAMP is based on PWL; it is defined in nyquist.lsp.
    ;

1.4. Predefined Constants
  For  convenience  and readability, Nyquist pre-defines some constants, mostly
based on the notation of the Adagio score language, as follows:

   - Dynamics Note: these dynamics values are subject to change.

         lppp = -12.0 (dB)
         lpp = -9.0
         lp = -6.0
         lmp = -3.0
         lmf = 3.0
         lf = 6.0
         lff = 9.0
         lfff = 12.0
         dB0 = 1.00
         dB1 = 1.122
         dB10 = 3.1623

   - Durations

         s = Sixteenth = 0.25
         i = eIghth = 0.5
         q = Quarter = 1.0
         h = Half = 2.0
         w = Whole = 4.0
         sd, id, qd, hd, wd = dotted durations.
         st, it, qt, ht, wt = triplet durations.

   - PitchesPitches are based on an A4 of 440Hz.  To achieve  a  different
     tuning,  set  *A4-Hertz*  to  the  desired frequency for A4, and call
     (set-pitch-names).  This will recompute the names listed below with a
     different  tuning.    In  all cases, the pitch value 69.0 corresponds
     exactly to 440Hz, but fractional values are allowed, so for  example,
     if  you  set *A4-Hertz* to 444 (Hz), then the symbol A4 will be bound
     to 69.1567, and C4 (middle  C),  which  is  normally  60.0,  will  be
     60.1567.

         c0 = 12.0
         cs0, df0 = 13.0
         d0 = 14.0
         ds0, ef0 = 15.0
         e0 = 16.0
         f0 = 17.0
         fs0, gf0 = 18.0
         g0 = 19.0
         gs0, af0 = 20.0
         a0 = 21.0
         as0, bf0 = 22.0
         b0 = 23.0
         c1 ... b1 = 24.0 ... 35.0
         c2 ... b2 = 36.0 ... 47.0
         c3 ... b3 = 48.0 ... 59.0
         c4 ... b4 = 60.0 ... 71.0
         c5 ... b5 = 72.0 ... 83.0
         c6 ... b6 = 84.0 ... 95.0
         c7 ... b7 = 96.0 ... 107.0
         c8 ... b8 = 108.0 ... 119.0

   - Miscellaneous)

         ny:all = ``all the samples'' (i.e. a big number) = 1000000000

1.5. More Examples
  More  examples  can  be  found  in  the directory demos, part of the standard
Nyquist release. In this directory, you will find the following and more:

   - Gong   sounds   by   additive   synthesis(demos/pmorales/b1.lsp   and
     demos/mateos/gong.lsp

   - Risset's spectral analysis of a chord (demos/pmorales/b2.lsp)

   - Bell     sounds     (demos/pmorales/b3.lsp,    demos/pmorales/e2.lsp,
     demos/pmorales/partial.lsp, and demos/mateos/bell.lsp)

   - Drum sounds by Risset (demos/pmorales/b8.lsp

   - Shepard tones (demos/shepard.lsp and demos/pmorales/b9.lsp)

   - Random signals (demos/pmorales/c1.lsp)

   - Buzz with formant filters (demos/pmorales/buzz.lsp

   - Computing samples directly in Lisp (using Karplus-Strong and physical
     modelling as examples) (demos/pmorales/d1.lsp

   - FM  Synthesis examples, including bell, wood drum, brass sounds, tuba
     sound          (demos/mateos/tuba.lsp     and     clarinet     sounds
     (demos/pmorales/e2.lsp

   - Rhythmic patterns (demos/rhythm_tutorial.htm
2. Behavioral Abstraction
  In  Nyquist,  all functions are subject to transformations.  You can think of
transformations as additional parameters to every function, and  functions  are
free  to use these additional parameters in any way.  The set of transformation
parameters  is  captured  in  what  is  referred  to  as   the   transformation
environment.  (Note that the term environment is heavily overloaded in computer
science.  This is yet another usage of the term.)

  Behavioral abstraction is the ability of functions to adapt their behavior to
the  transformation environment.  This environment may contain certain abstract
notions, such as loudness, stretching a sound in time, etc.  These notions will
mean  different  things  to  different  functions.   For example, an oscillator
should produce more periods of oscillation in order to stretch its output.   An
envelope,  on  the  other  hand,  might only change the duration of the sustain
portion of the envelope in order to stretch.  Stretching a  sample  could  mean
resampling it to change its duration by the appropriate amount.

  Thus,  transformations  in Nyquist are not simply operations on signals.  For
example, if I want to stretch a note, it does not make  sense  to  compute  the
note  first  and  then  stretch the signal.  Doing so would cause a drop in the
pitch.  Instead, a transformation modifies the  transformation  environment  in
which  the  note  is  computed.  Think of transformations as making requests to
functions.  It is up to the function to carry  out  the  request.    Since  the
function   is   always   in   complete  control,  it  is  possible  to  perform
transformations with ``intelligence;'' that is, the  function  can  perform  an
appropriate   transformation,   such  as  maintaining  the  desired  pitch  and
stretching only phase 3 of an envelope to obtain a longer note.

2.1. The Environment
  The transformation environment consists of a set of special  Lisp  variables.
These variables should not be read directly and should never be set directly by
the programmer.  Instead, there are  functions  to  read  them,  and  they  are
automatically  set  and  restored  by  transformation  operators, which will be
described below.

  The transformation environment consists of the following elements.   Although
each  element  has a ``standard interpretation,'' the designer of an instrument
or the composer of a complex behavior is free to interpret the  environment  in
any  way.    For  example,  a  change  in  *loud*  may  change timbre more than
amplitude, and *transpose* may be ignored by percussion instruments:

*warp*          Time transformation, including time shift,  time  stretch,  and
                continuous  time warp.  The value of *warp* is interpreted as a
                function from logical (local score) time  to  physical  (global
                real)  time.    Do  not  access  *warp* directly.  Instead, use
                (local-to-global t) to convert from a logical (local)  time  to
                physical   (global)   time.      Most   often,  you  will  call
                (local-to-global 0).  Several transformation operators  operate
                on *warp*, including at, stretch, and warp.

*loud*          Loudness,   expressed  in  decibels.    The  default  (nominal)
                loudness is 0.0 dB (no change).  Do not access *loud* directly.
                Instead,  use (get-loud) to get the current value of *loud* and
                either loud or loud-abs to modify it.

*transpose*     Pitch transposition, expressed in semitones.   (Default:  0.0).
                Do   not   access   *transpose*   directly.      Instead,   use
                (get-transpose) to get the current  value  of  *transpose*  and
                either transpose or transpose-abs to modify it.

*sustain*       The  ``sustain,''  ``articulation,'' ``duty factor,'' or amount
                by which to separate or overlap sequential notes.  For example,
                staccato might be expressed with a *sustain* of 0.5, while very
                legato playing might be expressed  with  a  *sustain*  of  1.2.
                Specifically,   *sustain*   stretches  the  duration  of  notes
                (sustain) without affecting the inter-onset time (the  rhythm).
                Do  not  access *sustain* directly.  Instead, use (get-sustain)
                to get the current value of *sustain*  and  either  sustain  or
                sustain-abs to modify it.

*start*         Start  time  of  a clipping region.  Note:  unlike the previous
                elements  of   the   environment,   *start*   has   a   precise
                interpretation:  no  sound  should be generated before *start*.
                This is implemented in all the low-level sound functions, so it
                can  generally  be ignored.  You can read *start* directly, but
                use extract or extract-abs to modify it.  Note 2: Due  to  some
                internal  confusion between the specified starting time and the
                actual starting time of a signal after clipping, *start* is not
                fully implemented.

*stop*          Stop  time of clipping region.  By analogy to *start*, no sound
                should be generated after this time.  *start* and *stop*  allow
                a  composer  to  preview  a  small  section  of  a work without
                computing it from beginning  to  end.    You  can  read  *stop*
                directly,  but  use extract or extract-abs to modify it.  Note:
                Due to some internal confusion between the  specified  starting
                time  and  the actual starting time of a signal after clipping,
                *stop* is not fully implemented.

*control-srate* Sample rate of  control  signals.    This  environment  element
                provides the default sample rate for control signals.  There is
                no formal distinction between a control  signal  and  an  audio
                signal.    You  can  read  *control-srate*  directly,  but  use
                control-srate or control-srate-abs to modify it.

*sound-srate*   Sample rate  of  musical  sounds.    This  environment  element
                provides  the  default sample rate for musical sounds.  You can
                read   *sound-srate*   directly,   but   use   sound-srate   or
                sound-srate-abs to modify it.

2.2. Sequential Behavior
  Previous  examples  have  shown  the  use  of  seq,  the  sequential behavior
operator.  We can now explain seq in terms of transformations.    Consider  the
simple expression:

    (play (seq (note c4 q) (note d4 i)))

The idea is to create the first note at time 0, and to start the next note when
the first  one  finishes.    This  is  all  accomplished  by  manipulating  the
environment.   In particular, *warp* is modified so that what is locally time 0
for the second note is transformed, or warped, to the logical stop time of  the
first note.

  One  way to understand this in detail is to imagine how it might be executed:
first, *warp* is set to an initial value that has no effect on time, and  (note
c4  q)  is  evaluated.  A sound is returned and saved.  The sound has an ending
time, which in this case will be 1.0 because the  duration  q  is  1.0.    This
ending  time,  1.0,  is  used  to construct a new *warp* that has the effect of
shifting time by 1.0.  The second note is evaluated, and will start at time  1.
The  sound that is returned is now added to the first sound to form a composite
sound, whose duration will be 2.0.  *warp* is restored to its initial value.

  Notice  that  the  semantics  of  seq  can   be   expressed   in   terms   of
transformations.  To generalize, the operational rule for seq is:  evaluate the
first behavior according to the  current  *warp*.    Evaluate  each  successive
behavior  with  *warp*  modified  to  shift the new note's starting time to the
ending time of the previous behavior.  Restore *warp* to its original value and
return a sound which is the sum of the results.

  In  the Nyquist implementation, audio samples are only computed when they are
needed, and the second part of the seq is not evaluated until the  ending  time
(called  the  logical  stop time) of the first part.  It is still the case that
when the second part is evaluated, it will see *warp* bound to the ending  time
of the first part.

  A  language  detail: Even though Nyquist defers evaluation of the second part
of the seq, the expression can reference variables according to  ordinary  Lisp
scope  rules.    This  is because the seq captures the expression in a closure,
which retains all of the variable bindings.

2.3. Simultaneous Behavior
  Another operator is sim, which invokes multiple behaviors at the  same  time.
For example,

    (play (scale 0.5 (sim (note c4 q) (note d4 i))))

will play both notes starting at the same time.

  The operational rule for sim is: evaluate each behavior at the current *warp*
and return the result.  The following section illustrates two concepts:  first,
a  sound  is  not  a  behavior,  and  second,  the  sim operator and and the at
transformation can be used to place sounds in time.

2.4. Sounds vs. Behaviors
  The following example loads a sound from a file in the current directory  and
stores it in a-snd:

    ; load a sound
    ;
    (setf a-snd (s-read "./demo-snd.snd" :srate 22050.0))

    ; play it
    ;
    (play a-snd)

  One might then be tempted to write the following:

    (seq a-snd a-snd)  ;WRONG!

Why  is this wrong? Recall that seq works by modifying *warp*, not by operating
on sounds.  So, seq will proceed by evaluating a-snd with different  values  of
*warp*.    However,  the result of evaluating a-snd (a Lisp variable) is always
the same sound, regardless of the environment; in this case, the  second  a-snd
should  start  at  time 0.0, just like the first. In this case, after the first
sound ends, Nyquist is unable to ``back up'' to time zero,  so  in  fact,  this
will  play  two  sounds  in sequence, but that is a result of an implementation
detail rather than correct program execution. In  fact,  a  future  version  of
Nyquist  might  (correctly)  stop  and report an error when it detects that the
second sound in the sequence has a real start time that is before the requested
one.

  How then do we obtain a sequence of two sounds properly?  What we really need
here is a behavior that transforms a  given  sound  according  to  the  current
transformation  environment.    That job is performed by cue.  For example, the
following will behave as expected, producing a sequence of two sounds:

    (seq (cue a-snd) (cue a-snd))

This example is correct because the second  expression  will  shift  the  sound
stored in a-snd to start at the end time of the first expression.

  The  lesson  here is very important: sounds are not behaviors!  Behaviors are
computations that generate sounds according to the transformation  environment.
Once  a  sound  has  been  generated,  it can be stored, copied, added to other
sounds, and used in many other  operations,  but  sounds  are  not  subject  to
transformations.    To  transform  a  sound,  use  cue, sound, or control.  The
differences between these operations are discussed later.  For now, here  is  a
``cue sheet'' style score that plays 4 copies of a-snd:

    ; use sim and at to place sounds in time
    ;
    (play (sim (at 0.0 (cue a-snd))
               (at 0.7 (cue a-snd))
               (at 1.0 (cue a-snd))
               (at 1.2 (cue a-snd))))

2.5. The At Transformation
  The  second  concept  introduced by the previous example is the at operation,
which shifts the *warp* component of the environment.  For example,

    (at 0.7 (cue a-snd))

can be explained operationally as follows: modify *warp* by shifting it by  0.7
and evaluate (cue a-snd).  Return the resulting sound after restoring *warp* to
its original value.  Notice how at is used inside a  sim  construct  to  locate
copies  of a-snd in time.  This is the standard way to represent a note-list or
a cue-sheet in Nyquist.

  This also explains why sounds need to be cue'd in order to be shifted in time
or arranged in sequence.  If this were not the case, then sim would take all of
its parameters (a set of sounds) and line them up to start at  the  same  time.
But  (at  0.7 (cue a-snd)) is just a sound, so sim would ``undo'' the effect of
at, making all of the sounds in the previous example start  simultaneously,  in
spite  of the at.  Since sim respects the intrinsic starting times of sounds, a
special operation, cue, is needed to create a new sound  with  a  new  starting
time.

2.6. Nested Transformations
  Transformations can be combined using nested expressions.  For example,

    (sim (cue a-snd)
         (loud 6.0 (at 3.0 (cue a-snd))))

scales the amplitude as well as shifts the second entrance of a-snd.

  Transformations can also be applied to groups of behaviors:

    (loud 6.0 (sim (at 0.0 (cue a-snd))
                   (at 0.7 (cue a-snd))))

2.7. Defining Behaviors
  Groups  of  behaviors  can  be  named using defun (we already saw this in the
definitions of note and note-env).  Here  is  another  example  of  a  behavior
definition and its use.  The definition has one parameter:

    (defun snds (dly)
      (sim (at 0.0 (cue a-snd))
           (at 0.7 (cue a-snd))
           (at 1.0 (cue a-snd))
           (at (+ 1.2 dly) (cue a-snd))))

    (play (snds 0.1))
    (play (loud 0.25 (stretch 0.9 (snds 0.3))))

In  the  last  line, snds is transformed: the transformations will apply to the
cue behaviors within snds.  The loud transformation will scale  the  sounds  by
0.25,  and  stretch  will apply to the shift (at) amounts 0.0, 0.7, 1.0, and (+
1.2 dly).  The sounds themselves  (copies  of  a-snd)  will  not  be  stretched
because cue never stretches sounds.

  Section 5.3 describes the full set of transformations.

2.8. Sample Rates
  The  global  environment  contains  *sound-srate*  and *control-srate*, which
determine the sample rates of  sounds  and  control  signals.    These  can  be
overridden   at   any   point   by   the  transformations  sound-srate-abs  and
control-srate-abs; for example,

    (sound-srate-abs 44100.0 (osc c4))

will compute a tone using a 44.1Khz sample rate.

  As with  other  components  of  the  environment,  you  should  never  change
*sound-srate*  or  *control-srate*  directly with setf or even let.  The global
environment is determined by two  additional  variables:  *default-sound-srate*
and  *default-control-srate*.    You  can  add lines like the following to your
init.lsp file to change the default global environment:

    (setf *default-sound-srate* 44100.0)
    (setf *default-control-srate* 1102.5)

If you have already started Nyquist  and  want  to  change  the  defaults,  the
following functions should be used:

    (set-control-srate 1102.5)(set-sound-srate 22050.0)

These modify the default values and reinitialize the Nyquist environment.
3. Continuous Transformations and Time Warps
  Nyquist  transformations  were  discussed in the previous chapter, but all of
the examples used scalar values.  For example, we saw the  loud  transformation
used  to  change  loudness  by  a  fixed  amount.  What if we want to specify a
crescendo, where the loudness changes gradually over time?

  It turns out that all transformations can accept signals as well as  numbers,
so  transformations  can be continuous over time.  This raises some interesting
questions about how to interpret continuous transformations.  Should a loudness
transformation  apply  to  the  internal  details  of a note or only affect the
initial loudness?  It might seem unnatural for a decaying piano note to perform
a  crescendo.    On  the  other hand, a sustained trumpet sound should probably
crescendo continuously.  In the case of time warping (tempo changes), it  might
be  best  for  a  drum  roll  to maintain a steady rate, a trill may or may not
change rates with tempo, and a run of sixteenth notes will  surely  change  its
rate.

  These  issues  are  complex,  and Nyquist cannot hope to automatically do the
right thing in all cases.   However,  the  concept  of  behavioral  abstraction
provides  an  elegant  solution.    Since  transformations  merely  modify  the
environment, behaviors are not forced to  implement  any  particular  style  of
transformation.    Nyquist  is  designed  so that the default transformation is
usually the right one, but it  is  always  possible  to  override  the  default
transformation to achieve a particular effect.

3.1. Simple Transformations
  The  ``simple''  transformations affect some parameter, but have no effect on
time itself.  The simple transformations  that  support  continuously  changing
parameters are: sustain, loud, and transpose.

  As  a first example, Let us use transpose to create a chromatic scale.  First
define a sequence of tones at a steady pitch:  (defun tone-seq  ()  (seqrep  (i
16)  (stretch  0.25  (osc-note  c4)))) Now define a linearly increasing ramp to
serve as a transposition function:  (defun pitch-rise () (stretch 4.0 (scale 16
(ramp))))  This  ramp  has  a  duration of 4 seconds, and over that interval it
rises from 0 to 16 (corresponding to the 16 semitones we  want  to  transpose).
Now,  pitch-rise  is  used  to  transpose  tone-seq:  (defun chromatic-scale ()
(transpose (pitch-rise) (tone-seq)))

  Similar transformations can be constructed to change the  sustain  or  ``duty
factor''  of  notes  and  their  loudness.   The following expression plays the
previously constructed chromatic scale with increasing  note  durations.    The
rhythm  is  unchanged,  but  the  note  length changes from staccato to legato:
(sustain (stretch 4 (sum 0.2 (ramp))) (chromatic-scale)) The resulting  sustain
function  will  ramp  from  0.2  to 1.2.  A sustain of 1.2 denotes a 20 percent
overlap between notes.  The sum has a stretch factor of 4, so  it  will  extend
over the 4 second duration of chromatic-scale.

  What  do  these  transformations  mean?  How did the system know to produce a
pitch rise rather than a continuous glissando?  This all relates to the idea of
behavioral  abstraction.    It  is  possible to design sounds that do glissando
under the transpose transform,  and  you  can  even  make  sounds  that  ignore
transpose  altogether.    As explained in Chapter 2, the transformations modify
the environment, and behaviors can reference the environment to determine  what
signals  to  generate.    All  built-in  functions, such as osc, have a default
behavior.

  The default behavior for sound primitives under transpose, sustain, and  loud
transformations  is  to  sample  the  environment at the beginning of the note.
Transposition is not quantized to semitones or any  other  scale,  but  in  our
example,  we  arranged  for the transposition to work out to integer numbers of
semitones, so we got a chromatic scale.

  Transposition only applies to the oscillator  and  sampling  primitives  osc,
partial,  sampler,  sine,  fmosc,  and amosc.  Sustain applies to osc, env, and
pwl. (Note that amosc and fmosc get their durations from the modulation signal,
so they may indirectly depend upon the sustain.)  Loud applies to osc, sampler,
cue, sound, fmosc, and amosc. (But not pwl or env.)

3.2. Time Warps
  The most interesting  transformations  have  to  do  with  transforming  time
itself.    The  warp  transformation  provides  a mapping function from logical
(score) time to real time.  The slope of this function tells us how many  units
of  real  time  are covered by one unit of score time.  This is proportional to
1/tempo.  A higher slope corresponds to a slower tempo.

  To demonstrate warp, we will define a time warp function using pwl:

    (defun warper ()
      (pwl .25 .4 .75 .6 1.0 1.0 2.0 2.0 2.0))

This function has an initial slope of .4/.25 = 1.6.  It may be easier to  think
in  reciprocal  terms:  the  initial  tempo is .25/.4 = .625.  Between 0.25 and
0.75, the tempo is .5/.2 = 2.5, and from 0.75 to 1.0, the tempo is again  .625.
It  is important for warp functions to completely span the interval of interest
(in our case it will be 0 to 1), and it is safest to extend a  bit  beyond  the
interval,  so  we  extend the function on to 2.0 with a tempo of 1.0.  Next, we
stretch and scale the warper function to cover 4 seconds of score  time  and  4
seconds of real time:

    (defun warp4 () (stretch 4 (scale 4 (warper))))























     Figure 2:  The result of (warp4), intended to map 4 seconds of  score
     time into 4 seconds of real time.   The  function  extends  beyond  4
     seconds  (the dashed lines) to make sure the function is well-defined
     at  location (4, 4).  Nyquist  sounds  are  ordinarily  open  on  the
     right.


  Figure  2  shows a plot of this warp function.  Now, we can warp the tempo of
the tone-seq defined above using warp4:

    (play (warp (warp4) (tone-seq)))

Figure 3 shows the result graphically.  Notice that the durations of the  tones
are  warped  as well as their onsets.  Envelopes are not shown in detail in the
figure.  Because of the way env is defined, the tones will have constant attack
and decay times, and the sustain will be adjusted to fit the available time.














     Figure 3:  When  (warp4)  is applied to (tone-seq-2), the note onsets
     and durations are warped.


3.3. Abstract Time Warps
  We have seen a number of examples where the default behavior did the  ``right
thing,''  making  the  code  straightforward.    This  is  not always the case.
Suppose we want to warp the note onsets but not the durations.  We  will  first
look  at  an  incorrect solution and discuss the error.  Then we will look at a
slightly more complex (but correct) solution.

  The default behavior for most Nyquist built-in functions  is  to  sample  the
time  warp  function  at  the  nominal  starting  and ending score times of the
primitive.  For many built-in functions, including osc,  the  starting  logical
time  is  0  and  the  ending  logical  time is 1, so the time warp function is
evaluated at these points to yield real starting and stopping times, say  15.23
and  16.79.   The difference (e.g. 1.56) becomes the signal duration, and there
is no internal time warping.  The pwl function behaves  a  little  differently.
Here,  each  breakpoint  is  warped individually, but the resulting function is
linear between the breakpoints.

  A consequence of the default behavior is that notes stretch  when  the  tempo
slows  down.    Returning  to our example, recall that we want to warp only the
note onset times and not the duration.  One  would  think  that  the  following
would work:

    (defun tone-seq-2 ()
      (seqrep (i 16)
              (stretch-abs 0.25 (osc-note c4))))

    (play (warp (warp4) (tone-seq-2)))

Here,  we  have  redefined tone-seq, renaming it to tone-seq-2 and changing the
stretch to stretch-abs.  The stretch-abs should override the warp function  and
produce a fixed duration.

  If  you  play  the  example,  you  will  hear  steady sixteenths and no tempo
changes.  What is wrong?  In a sense, the ``fix'' works too well.  Recall  that
sequences  (including seqrep) determine the starting time of the next note from
the logical stop time of the previous sound in the sequence.   When  we  forced
the  stretch to 0.25, we also forced the logical stop time to 0.25 real seconds
from the beginning, so every note starts 0.25 seconds after the  previous  one,
resulting in a constant tempo.

  Now  let  us  design  a  proper solution.  The trick is to use stretch-abs as
before to control the duration, but to restore the logical stop time to a value
that results in the proper inter-onset time interval:

    (defun tone-seq-3 ()
      (seqrep (i 16)
              (set-logical-stop
                 (stretch-abs 0.25 (osc-note c4))
                 0.25)))

    (play (warp (warp4) (tone-seq-3)))
Notice the addition of set-logical-stop enclosing the stretch-abs expression to
set the logical stop time.  A possible point of  confusion  here  is  that  the
logical  stop  time  is set to 0.25, the same number given to stretch-abs!  How
does setting the logical stop time to 0.25 result in a tempo change?  When used
within a warp transformation, the second argument to set-logical-stop refers to
score time rather than real time.  Therefore, the score  duration  of  0.25  is
warped  into  real  time,  producing tempo changes according to the enviroment.
Figure 4 illustrates the result graphically.














     Figure 4:  When (warp4) is applied  to (tone-seq-3), the note  onsets
     are  warped,  but  not  the  duration,  which remains a constant 0.25
     seconds.  In the fast middle section, this  causes notes to  overlap.
     Nyquist will sum (mix) them.


3.4. Nested Transformations
  Transformations  can  be nested.  In particular, a simple transformation such
as transpose can be nested within a time warp transformation.  Suppose we  want
to  warp  our chromatic scale example with the warp4 time warp function.  As in
the previous section, we will show an erroneous simple solution followed  by  a
correct one.

  The  simplest  approach  to a nested transformation is to simply combine them
and hope for the best:

    (play (warp (warp4)
                (transpose (pitch-rise) (tone-seq))))

This example will not work the way you might expect.  Here  is  why:  the  warp
transformation  applies  to  the  (pitch-rise) expression, which is implemented
using the ramp function.  The  default  behavior  of  ramp  is  to  interpolate
linearly (in real time) between two points.  Thus, the ``warped'' ramp function
will not truly reflect the internal details of the intended time warp.  What we
need  is a way to properly compose the warp and ramp functions.  This will lead
to a correct solution.

  Here is the modified code to properly warp a transposed sequence.  Note  that
the  original  sequence is used without modification.  The only complication is
producing a properly warped transposition function:

    (play (warp (warp4)
                (transpose
                    (control-warp (get-warp)
                                  (warp-abs nil (pitch-rise)))
                    (tone-seq))))

To properly warp the pitch-rise transposition function,  we  use  control-warp,
which  applies a warp function to a function of score time, yielding a function
of real time.  We need to pass the warp desired function to control-warp, so we
fetch  it  from  the environment ith (get-warp).  Finally, since the warping is
done here, we want to shield the pitch-rise expression from further warping, so
we enclose it in (warp-abs nil ...).

  An  aside:  This  last  example  illustrates  a  difficulty  in the design of
Nyquist.  To support behavioral abstraction  universally,  we  must  rely  upon
behaviors  to  ``do  the  right  thing.''  In this case, we would like the ramp
function to warp continuously according  to  the  environment.    But  this  is
inefficient  and  unnecessary in many other cases where ramp and especially pwl
are used.  (pwl warps its breakpoints, but still interpolates linearly  between
them.)   Also, if the default behavior of primitives is to warp in a continuous
manner, this makes it difficult to build custom abstract behaviors.  The  final
vote is not in.
4. More Examples
  This  chapter  explores  Nyquist through additional examples.  The reader may
wish to browse through these and move on to Chapter 5,  which  is  a  reference
section describing Nyquist functions.

4.1. Stretching Sampled Sounds
  This  example  illustrates  how  to  stretch  a  sound,  resampling it in the
process.  Because sounds in Nyquist are values that contain  the  sample  rate,
start  time,  etc.,  use  sound  to convert a sound into a behavior that can be
stretched, e.g. (sound a-snd). This behavior stretches a sound according to the
stretch  factor  in  the  environment,  set  using  stretch.  For  accuracy and
efficiency, Nyquist does  not  resample  a  stretched  sound  until  absolutely
necessary.  The  force-srate function is used to resample the result so that we
end up with a ``normal'' sample rate that is playable on ordinary sound cards.

    ; if a-snd is not loaded, load sound sample:
    ;
    (if (not (boundp 'a-snd))
        (setf a-snd
           (s-read "demo-snd.nh" :srate 22050.0)))

    ; the SOUND operator shifts, stretches, clips and scales
    ; a sound according to the current environment
    ;
    (play (force-srate *default-sound-srate*
                       (stretch 3.0 (sound a-snd))))

    (defun down ()
      (force-srate *default-sound-srate*
        (seq (stretch 0.2 (sound a-snd))
             (stretch 0.3 (sound a-snd))
             (stretch 0.4 (sound a-snd))
             (stretch 0.5 (sound a-snd))
             (stretch 0.6 (sound a-snd)))))

    (play (down))

    ; that was so much fun, let's go back up:
    ;
    (defun up ()
      (force-srate *default-sound-srate*
        (seq (stretch 0.5 (sound a-snd))
             (stretch 0.4 (sound a-snd))
             (stretch 0.3 (sound a-snd))
             (stretch 0.2 (sound a-snd)))))

    ; and write a sequence
    ;
    (play (seq (down) (up) (down)))


  Notice the use of the sound behavior as opposed to cue.    The  cue  behavior
shifts  and  scales  its  sound according to *warp* and *loud*, but it does not
change the duration or resample the sound.  In contrast, sound not only  shifts
and  scales  its  sound, but it also stretches it by resampling or changing the
effective sample rate according to *warp*.  If *warp* is a  continuous  warping
function,  then  the  sound  will  be  stretched by time-varying amounts.  (The
*transpose* element of the environment is ignored by both cue and sound.)

  Note:  sound  may  use  linear  interpolation  rather  than  a   high-quality
resampling  algorithm.    In  some  cases, this may introduce errors audible as
noise. Use resample (see Section 5.2.2) for high-quality interpolation.

  In the functions up and down, the *warp* is  set  by  stretch,  which  simply
scales time by a constant scale factor. In this case, sound can ``stretch'' the
signal simply by changing the sample rate without any further computation. When
seq  tries  to  add  the signals together, it discovers the sample rates do not
match and uses linear interpolation to adjust all sample rates to match that of
the  first  sound  in  the  sequence. The result of seq is then converted using
force-srate to convert the sample rate, again using  linear  interpolation.  It
would be slightly better, from a computational standpoint, to apply force-srate
individually to each stretched sound rather  than  applying  force-srate  after
seq.

  Notice  that the overall duration of (stretch 0.5 (sound a-snd)) will be half
the duration of a-snd.

4.2. Saving Sound Files
  So far, we have used the play function to play a sound.   The  play  function
works  by  writing  a sound to a file and then running a system program to play
the file.  This can be done one step at a time, and it is often  convenient  to
save a sound to a particular file for later use:

    ; write the sample to a file,
    ;    the file name can be any Unix filename.  Prepending a "./" tells
    ;    s-save to not prepend *default-sf-dir*
    ;
    (s-save a-snd 1000000000 "./a-snd-file.snd")

    ; play a file
    ; (only works if you have a Unix program called "play")
    (system "play a-snd-file.snd")

    ; delete the file (do this with care!)
    ;
    (system "rm a-snd-file.snd")


    ; now let's do it using a variable as the file name
    ;
    (setf my-sound-file "./a-snd-file.snd")

    (s-save a-snd 1000000000 my-sound-file)

    (system (strcat "play " my-sound-file))

    (system (strcat "rm " my-sound-file))


This example shows how s-save can be used to save a sound to a file.

  This  example  also  shows how the system function can be used to invoke Unix
shell commands, such as a command to play a file or remove it.  Finally, notice
that  strcat can be used to concatenate a command name to a file name to create
a complete command that is then passed to system.  (This is convenient  if  the
sound file name is stored in a parameter or variable.)

  Instead  of using system, you should generally use play-file if you just want
to play a file, e.g.

    ; play a sound file, works on any operating system
    (play-file "./a-snd-file.snd")
    ; play the file whose name is the value of a variable:
    (play-file my-sound-file)

4.3. Memory Space and Normalization
  Sound samples take up lots of memory, and often, there is not enough  primary
(RAM)  memory  to  hold  a  complete composition.  For this reason, Nyquist can
compute sounds incrementally, saving  the  final  result  on  disk.    However,
Nyquist  can also save sounds in memory so that they can be reused efficiently.
In general, if a sound is saved in a global variable, memory will be  allocated
as needed to save and reuse it.

  The  standard  way  to  compute  a  sound  and write it to disk is to pass an
expression to the play command:

    (play (my-composition))

  Often it is nice to normalize sounds so that  they  use  the  full  available
dynamic  range  of  16  bits.    Nyquist has an automated facility to help with
normalization. By default, Nyquist computes up  to  1  million  samples  (using
about  4MB  of  memory) looking for the peak. The entire sound is normalized so
that this peak will not cause clipping. If the sound has less  than  1  million
samples,  or  if the first million samples are a good indication of the overall
peak, then the signal will not clip.

  With this automated normalization technique, you can choose the desired  peak
value by setting *autonorm-target*, which is initialized to 0.9.  The number of
samples examined is *autonorm-max-samples*, initially 1 million. You  can  turn
this feature off by executing:

    (autonorm-off)

and turn it back on by typing:

    (autonorm-on)

This  normalization  technique is in effect when *autonorm-type* is 'lookahead,
which is the default.

  An alternative normalization method uses the peak  value  from  the  previous
call to play. After playing a file, Nyquist can adjust an internal scale factor
so that  if  you  play  the  same  file  again,  the  peak  amplitude  will  be
*autonorm-target*,  which is initialized to 0.9. This can be useful if you want
to carefully normalize a big sound  that  does  not  have  its  peak  near  the
beginning.  To  select  this style of normalization, set *autonorm-type* to the
quoted atom 'previous.

  You can also create your own normalization  method  in  Nyquist.    The  peak
function  computes  the  maximum  value  of  a  sound.   The peak value is also
returned from the play macro. You can normalize in memory if  you  have  enough
memory;  otherwise  you  can  compute  the sound twice.  The two techniques are
illustrated here:

    ; normalize in memory.  First, assign the sound to a variable so
    ; it will be retained:
    (setf mysound (sim (osc c4) (osc c5)))
    ; now compute the maximum value (ny:all is 1 giga-samples, you may want
    ; smaller constant if you have less than 4GB of memory:
    (setf mymax (peak mysound NY:ALL))
    (display "Computed max" mymax)
    ; now write out and play the sound from memory with a scale factor:
    (play (scale (/ 1.0 mymax) mysound))

    ; if you don't have space in memory, here's how to do it:
    (defun myscore () (sim (osc c4) (osc c5)))
    ; compute the maximum:
    (setf mymax (peak (myscore) NY:ALL))
    (display "Computed max" mymax)
    ; now we know the max, but we don't have a the sound (it was garbage
    ; collected and never existed all at once in memory).  Compute the soun
    ; again, this time with a scale factor:
    (play (scale (/ 1.0 mymax) (myscore)))

  You can also write a sound as a floating point file.  This file can  then  be
converted  to  16-bit  integer  with  the  proper  scaling  applied.  If a long
computation was involved, it should be much faster to  scale  the  saved  sound
file than to recompute the sound from scratch.  Although not implemented yet in
Nyquist, some header formats can store maximum amplitudes, and  some  soundfile
player  programs  can  rescale  floating  point  files  on  the  fly,  allowing
normalized soundfile playback without an extra normalization  pass  (but  at  a
cost  of  twice  the  disk  space  of  16-bit samples).  You can use Nyquist to
rescale a floating point file and convert it to 16-bit samples for playback.

4.4. Frequency Modulation
  The next example uses the Nyquist  frequency  modulation  behavior  fmosc  to
generate various sounds.  The parameters to fmosc are:

    (fmosc pitch modulator table phase)

Note  that pitch is the number of half-steps, e.g. c4 has the value of 60 which
is middle-C, and phase is in degrees.    Only  the  first  two  parameters  are
required:

    ; make a short sine tone with no frequency modulation
    ;
    (play (fmosc c4 (pwl 0.1)))

    ; make a longer sine tone -- note that the duration of
    ;   the modulator determines the duration of the tone
    ;
    (play (fmosc c4 (pwl 0.5)))

In  the  example  above, pwl (for Piece-Wise Linear) is used to generate sounds
that are zero for the durations of 0.1  and  0.5  seconds,  respectively.    In
effect,  we are using an FM oscillator with no modulation input, and the result
is a sine tone.  The duration of the modulation determines the duration of  the
generated tone (when the modulation signal ends, the oscillator stops).

  The  next  example  uses  a more interesting modulation function, a ramp from
zero to C , expressed in hz.  More explanation  of  pwl  is  in  order.    This
         4
operation   constructs   a   piece-wise   linear   function   sampled   at  the
*control-srate*.  The first breakpoint is always at (0, 0), so  the  first  two
parameters  give  the  time  and value of the second breakpoint, the second two
parameters give the time and value of the third breakpoint, and  so  on.    The
last  breakpoint  has  a value of 0, so only the time of the last breakpoint is
given.  In this case, we want the ramp to end at C ,  so  we  cheat  a  bit  by
                                                  4
having the ramp return to zero ``almost'' instantaneously between times 0.5 and
0.501.

  The pwl behavior always expects an odd number of parameters.   The  resulting
function  is  shifted  and  stretched  linearly  according  to  *warp*  in  the
environment.  Now, here is the example:

    ; make a frequency sweep of one octave; the piece-wise linear function
    ; sweeps from 0 to (step-to-hz c4) because, when added to the c4
    ; fundamental, this will double the frequency and cause an octave sweep
    ;
    (play (fmosc c4 (pwl 0.5 (step-to-hz c4) 0.501)))

  The same idea can be applied to a non-sinusoidal carrier.   Here,  we  assume
that *fm-voice* is predefined (the next section shows how to define it):

    ; do the same thing with a non-sine table
    ;
    (play (fmosc cs2 (pwl 0.5 (step-to-hz cs2) 0.501)
                 *fm-voice* 0.0))

  The next example shows how a function can be used to make a special frequency
modulation contour.  In this case the contour generates a sweep from a starting
pitch to a destination pitch:

    ; make a function to give a frequency sweep, starting
    ; after <delay> seconds, then sweeping from <pitch-1>
    ; to <pitch-2> in <sweep-time> seconds and then
    ; holding at <pitch-2> for <hold-time> seconds.
    ;
    (defun sweep (delay pitch-1 sweep-time pitch-2 hold-time)
      (let ((interval (- (step-to-hz pitch-2)
                         (step-to-hz pitch-1))))
        (pwl delay 0.0
             ; sweep from pitch 1 to pitch 2
             (+ delay sweep-time) interval
             ; hold until about 1 sample from the end
             (+ delay sweep-time hold-time -0.0005) interval
             ; quickly ramp to zero (pwl always does this,
             ;    so make it short)
             (+ delay sweep-time hold-time))))


    ; now try it out
    ;
    (play (fmosc cs2 (sweep 0.1 cs2 0.6 gs2 0.5)
                 *fm-voice* 0.0))

  FM can be used for vibrato as well as frequency sweeps.  Here, we use the lfo
function to generate vibrato.  The lfo operation is similar to osc,  except  it
generates  sounds at the *control-srate*, and the parameter is hz rather than a
pitch:

    (play (fmosc cs2 (scale 10.0 (lfo 6.0))
                 *fm-voice* 0.0))

  What kind of manual would this be without the obligatory FM sound?   Here,  a
sinusoidal  modulator  (frequency C ) is multiplied by a slowly increasing ramp
                                   4
from zero to 1000.0.

    (setf modulator (mult (pwl 1.0 1000.0 1.0005)
                            (osc c4)))

    ; make the sound
    (play (fmosc c4 modulator))

  For more simple examples of FM  in  Nyquist,  see  demos/warble_tutorial.htm.
Another  interesting FM sound reminiscent of ``scratching'' can be found with a
detailed explanation in demos/scratch_tutorial.htm..

4.5. Building a Wavetable
  In Section 1.3.1, we saw how to synthesize a wavetable.  A wavetable for  osc
also  can  be  extracted from any sound.  This is especially interesting if the
sound is digitized from some external sound source and loaded using the  s-read
function.    Recall  that a table is a list consisting of a sound, the pitch of
that sound, and T (meaning the sound is periodic).

  In the following, a sound is first read from the file demo-snd.nh.  Then, the
extract  function  is used to extract the portion of the sound between 0.110204
and 0.13932 seconds.  (These numbers might be obtained by  first  plotting  the
sound  and  estimating  the  beginning  and  end  of a period, or by using some
software to look for good zero crossings.)  The result of extract  becomes  the
first  element  of  a list.  The next element is the pitch (24.848422), and the
last element is T.  The list is assigned to *fm-voice*.

    (if (not (boundp 'a-snd))
        (setf a-snd (s-read "demo-snd.nh" :srate 22050.0)))

    (setf *fm-voice* (list
                      (extract 0.110204 0.13932 (cue a-snd))
                      24.848422
                      T))

  The file  examples.lsp  contains  an  extensive  example  of  how  to  locate
zero-crossings,  extract  a  period, build a waveform, and generate a tone from
it.  (See ex37 through ex40 in the file.)

4.6. Filter Examples
  Nyquist provides a variety of filters.  All of these filters take either real
numbers  or signals as parameters.  If you pass a signal as a filter parameter,
the filter coefficients are recomputed  at  the  sample  rate  of  the  control
signal.   Since filter coefficients are generally expensive to compute, you may
want to select filter control rates carefully.  Use control-srate-abs  (Section
5.3)  to  specify  the default control sample rate, or use force-srate (Section
5.2.2) to resample a signal before passing it to a filter.

  Before presenting examples, let's generate some unfiltered white noise:

    (play (noise))

Now low-pass filter the noise with a 1000Hz cutoff:

    (play (lp (noise) 1000.0))

The high-pass filter is the inverse of the low-pass:

    (play (hp (noise) 1000.0))

  Here is a low-pass filter sweep from 100Hz to 2000Hz:

    (play (lp (noise) (pwl 0.0 100.0 1.0 2000.0 1.0))))

And a high-pass sweep from 50Hz to 4000Hz:

    (play (hp (noise) (pwl 0.0 50.0 1.0 4000.0 1.0)))

  The band-pass filter takes a center  frequency  and  a  bandwidth  parameter.
This  example  has  a  500Hz center frequency with a 20Hz bandwidth.  The scale
factor is necessary because, due to the resonant peak of the filter, the signal
amplitude exceeds 1.0:

    (play (reson (scale 0.005 (noise)) 500.0 20.0)))

In  the next example, the center frequency is swept from 100 to 1000Hz, using a
constant 20Hz bandwidth:

    (play (reson (scale 0.005 (noise))
                 (pwl 0.0 100.0 1.0 1000.0 1.0) 20.0)))

  For another example with explanations, see demos/wind_tutorial.htm.

4.7. DSP in Lisp
  In almost any signal processing system,  the  vast  majority  of  computation
takes  place  in  the inner loops of DSP algorithms, and Nyquist is designed so
that these time-consuming inner loops  are  in  highly-optimized  machine  code
rather  than  relatively  slow  interpreted  lisp  code.  As  a result, Nyquist
typically spends 95% of its time in these inner loops; the overhead of using  a
Lisp interpreter is negligible.

  The drawback is that Nyquist must provide the DSP operations you need, or you
are out of luck. When Nyquist is found lacking, you  can  either  write  a  new
primitive signal operation, or you can perform DSP in Lisp code. Neither option
is  recommended  for  inexperienced  programmers.  Instructions  for  extending
Nyquist  are given in Appendix I. This section describes the process of writing
a new signal processing function in Lisp.

  Before implementing a new DSP function, you should decide which  approach  is
best.  First,  figure out how much of the new function can be implemented using
existing Nyquist functions. For example, you might think  that  a  tapped-delay
line  would  require  a  new  function,  but  in fact, it can be implemented by
composing  sound  transformations  to  accomplish  delays,  scale  factors  for
attenuation,  and  additions to combine the intermediate results.  This can all
be packaged into a new Lisp function, making it easy to use.  If  the  function
relies on built-in DSP primitives, it will execute very efficiently.

  Assuming  that  built-in  functions  cannot  be  used,  try  to  define a new
operation that will be both simple and general.  Usually,  it  makes  sense  to
implement  only  the  kernel  of  what  you  need,  combining  it with existing
functions to build a complete instrument or operation.   For  example,  if  you
want to implement a physical model that requires a varying breath pressure with
noise and vibrato, plan to use  Nyquist  functions  to  add  a  basic  pressure
envelope  to  noise  and  vibrato  signals to come up with a composite pressure
signal. Pass that signal into the physical model rather than  synthesizing  the
envelope,  noise,  and  vibrato  within the model. This not only simplifies the
model, but gives you the flexibility to use  all  of  Nyquist's  operations  to
synthesize a suitable breath pressure signal.

  Having  designed  the  new ``kernel'' DSP operation that must be implemented,
decide whether to use C or Lisp. To use C, you must have a C compiler, the full
source  code for Nyquist, and you must learn about extending Nyquist by reading
Appendix I. This is the more complex approach, but  the  result  will  be  very
efficient.  A  C  implementation  will  deal  properly with sounds that are not
time-aligned or matched in sample rates.  To use Lisp, you must learn something
about  the  XLISP  object  system, and the result will be about 50 times slower
than C. Also, it is more difficult to deal with time alignment and  differences
in  sample  rates.    The  remainder of this section gives an example of a Lisp
version of snd-prod to illustrate how to write DSP  functions  for  Nyquist  in
Lisp.

  The  snd-prod  function  is  the low-level multiply routine. It has two sound
parameters and returns a sound which is the product of the two. To keep  things
simple,  we  will assume that two sounds to be multiplied have a matched sample
rate and matching start times. The DSP algorithm  for  each  output  sample  is
simply  to  fetch  a  sample  from  each  sound,  multiply them, and return the
product.

  To implement snd-prod in Lisp, three components are required:

   1. An object is used to store the two  parameter  sounds.  This  object
      will be called upon to yield samples of the result sound;

   2. Within  the  object,  the snd-fetch routine is used to fetch samples
      from the two input sounds as needed;

   3. The result must be of type  SOUND,  so  snd-fromobject  is  used  to
      create the result sound.

  The  combined  solution  will  work as follows: The result is a value of type
sound that retains a reference to the object.  When Nyquist needs samples  from
the  sound,  it  invokes the sound's ``fetch'' function, which in turn sends an
XLISP message to the object. The object will use snd-fetch to get a sample from
each stored sound, multiply the samples, and return a result.

  Thus  the  goal  is  to  design  an XLISP object that, in response to a :next
message will return a proper sequence of samples.  When the sound  reaches  the
termination time, simply return NIL.

  The  XLISP manual (see Appendix IV describes the object system, but in a very
terse style, so this example will include some explanation of  how  the  object
system  is  used.  First,  we  need to define a class for the objects that will
compute sound products. Every class is a  subclass  of  class  class,  and  you
create a subclass by sending :new to a class.

    (setf product-class (send class :new '(s1 s2)))

The  parameter  '(s1  s2)  says  that  the  new  class  will  have two instance
variables, s1 and s2. In other words, every object  which  is  an  instance  of
class product-class will have its own copy of these two variables.

  Next, we will define the :next method for product-class:

    (send product-class :answer :next '()
      '((let ((f1 (snd-fetch s1))
              (f2 (snd-fetch s2)))
          (cond ((and f1 f2)
                 (* f1 f2))
                (t nil)))))

The  :answer message is used to insert a new method into our new product-class.
The method is described in three parts: the  name  (:next),  a  parameter  list
(empty  in this case), and a list of expressions to be evaluated. In this case,
we fetch samples from s1 and s2. If both are numbers, we return their  product.
If either is NIL, we terminate the sound by returning nil.

  The  :next  method  assumes  that s1 and s2 hold the sounds to be multiplied.
These must be installed when the object is created.   Objects  are  created  by
sending  :new to a class. A new object is created, and any parameters passed to
:new are then sent in a :isnew message to the new object. Here  is  the  :isnew
definition for product-class:

    (send product-class :answer :isnew '(p1 p2)
      '((setf s1 (snd-copy p1))
        (setf s2 (snd-copy p2))))

Take  careful note of the use of snd-copy in this initialization. The sounds s1
and s2 are modified when accessed by snd-fetch  in  the  :next  method  defined
above,  but  this  destroys  the illusion that sounds are immutable values. The
solution is to copy the sounds before accessing them; the original  sounds  are
therefore  unchanged.    (This copy also takes place implicitly in most Nyquist
sound functions.)

  To make this code safer for general use, we should add checks that s1 and  s2
are  sounds  with  identical  starting  times  and  sample rates; otherwise, an
incorrect result might be computed.

  Now we are  ready  to  write  snd-product,  an  approximate  replacement  for
snd-prod:

    (defun snd-product (s1 s2)
      (let (obj)
        (setf obj (send product-class :new s1 s2))
        (snd-fromobject (snd-t0 s1) (snd-srate s1) obj)))

This  code  first creates obj, an instance of product-class, to hold s1 and s2.
Then, it uses obj to  create  a  sound  using  snd-fromobject.  This  sound  is
returned  from snd-product.  Note that in snd-fromobject, you must also specify
the starting time and sample rate as the first two parameters. These are copied
from  s1, again assuming that s1 and s2 have matching starting times and sample
rates.

  Note that in more elaborate DSP algorithms we could expect the object to have
a  number  of  instance  variables  to  hold  things  such as previous samples,
waveform tables, and other parameters.
5. Nyquist Functions
  This chapter provides a language  reference  for  Nyquist.    Operations  are
categorized  by functionality and abstraction level.  Nyquist is implemented in
two important levels: the ``high level'' supports behavioral abstraction, which
means  that operations like stretch and at can be applied.  These functions are
the ones that typical users are expected to use, and most  of  these  functions
are written in XLISP.

  The  ``low-level'' primitives directly operate on sounds, but know nothing of
environmental variables (such as *warp*, etc.).  The names  of  most  of  these
low-level  functions start with ``snd-''.  In general, programmers should avoid
any function with  the  ``snd-''  prefix.    Instead,  use  the  ``high-level''
functions, which know about the environment and react appropriately.  The names
of high-level functions do not have prefixes like the low-level functions.

  There are certain low-level operations that  apply  directly  to  sounds  (as
opposed  to behaviors) and are relatively ``safe'' for ordinary use.  These are
marked as such.

  Nyquist uses both linear frequency and  equal-temperament  pitch  numbers  to
specify  repetition  rates.  Frequency is always specified in either cycles per
second (hz), or pitch numbers, also referred to as ``steps,'' as  in  steps  of
the chromatic scale.  Steps are floating point numbers such that 60 = Middle C,
61 = C#, 61.23 is C# plus 23 cents, etc.  The  mapping  from  pitch  number  to
frequency  is the standard exponential conversion, and fractional pitch numbers
                             (pitch-69)/12
are allowed:  frequency=440*2             .  There are  many  predefined  pitch
names.    By default these are tuned in equal temperament, with A4 = 440Hz, but
these may be changed.  (See Section 1.4).

5.1. Sounds
  A sound is a primitive data type in Nyquist.  Sounds can be  created,  passed
as  parameters,  garbage  collected,  printed,  and  set to variables just like
strings, atoms, numbers, and other data types.



5.1.1. What is a Sound?
  Sounds have 5 components:

   - srate M the sample rate of the sound.

   - samples M the samples.

   - signal-start M the time of the first sample.

   - signal-stop M the time of one past the last sample.

   - logical-stop M the time at which the sound  logically  ends,  e.g.  a
     sound  may  end  at the beginning of a decay.  This value defaults to
     signal-stop, but may be set to any value.

It may seem that there should be  logical-start  to  indicate  the  logical  or
perceptual  beginning  of  a  sound  as  well as a logical-stop to indicate the
logical ending of a sound.  In practice,  only  logical-stop  is  needed;  this
attribute  tells when the next sound should begin to form a sequence of sounds.
In this respect, Nyquist sounds are  asymmetric:  it  is  possible  to  compute
sequences  forward in time by aligning the logical start of each sound with the
logical-stop of  the  previous  one,  but  one  cannot  compute  ``backwards'',
aligning the logical end of each sound with the logical start of its successor.
The root of this asymmetry is the fact that when we invoke a behavior,  we  say
when  to  start,  and the result of the behavior tells us its logical duration.
There is no way to invoke a behavior with a direct  specification  of  when  to
stop[Most  behaviors  will  stop  at time 1, warped according to *warp* to some
real time, but this is by convention and is not a direct specification.].

  Note: there is no way to enforce the intended  ``perceptual''  interpretation
of  logical-stop.    As  far as Nyquist is concerned, these are just numbers to
guide the alignment of sounds within various control constructs.



5.1.2. Multichannel Sounds
  Multichannel sounds are represented by Lisp arrays of sounds.  To  create  an
array  of  sounds  the XLISP vector function is useful.  Most low-level Nyquist
functions (the ones starting with snd-) do not operate on multichannel  sounds.
Most high-level functions do operate on multichannel sounds.



5.1.3. Accessing and Creating Sound
  Several  functions  display information concerning a sound and can be used to
query the components of a sound. There are functions that access samples  in  a
sound and functions that construct sounds from samples.

(sref sound time)
     Accesses sound at the point time, which is a local time. If time does  not
     correspond  to  a  sample  time,  then  the  nearest  samples are linearly
     interpolated to form the result.  To access a  particular  sample,  either
     convert  the  sound  to an array (see snd-samples below), or use snd-srate
     and snd-t0 (see below) to find the sample  rate  and  starting  time,  and
     compute  a  time  (t)  from the sample number (n):t=(n/srate)+t0 Thus, the
                              th
     lisp code to access the n   sample of a sound  would  look  like:    (sref
     sound  (global-to-local  (+ (/ n (snd-srate sound)) (snd-t0 sound)))) Here
     is why sref interprets its time argument as a local time:  >  (sref  (ramp
     1) 0.5) ; evaluate a ramp at time 0.5 0.5 > (at 2.0 (sref (ramp 1) 0.5)) ;
     ramp is shifted to start at 2.0 ; the time, 0.5, is shifted to 2.5 0.5  If
     you  were  to  use snd-sref, which treats time as global, instead of sref,
     which treats time as local, then the first example above would return  the
     same  answer  (0.5),  but the second example would return 0.  Why? Because
     the (ramp 1) behavior would be shifted to  start  at  time  2.0,  but  the
     resulting  sound  would  be  evaluated at global time 0.5.  By definition,
     sounds have a value of zero before their start time.

(sref-inverse sound value)
     Search sound for the first point at which it achieves value and return the
     corresponding (linearly interpolated) time.   If  no  inverse  exists,  an
     error  is  raised.  This function is used by Nyquist in the implementation
     of time warping.

(snd-from-array t0 sr array)
     Converts  a  lisp  array of FLONUMs into a sound with starting time t0 and
     sample rate sr.   Safe  for  ordinary  use.    Be  aware  that  arrays  of
     floating-point  samples use 14 bytes per sample, and an additional 4 bytes
     per sample are allocated by this function to create a sound type.

(snd-fromarraystream t0sr object)
     Creates  a  sound for which samples come from object. The starting time is
     t0 (a FLONUM), and the sample rate is sr. The object is  an  XLISP  object
     (see Section IV.11 for information on objects.) A sound is returned.  When
     the sound needs samples, they are generated by sending the  message  :next
     to  object. If object returns NIL, the sound terminates. Otherwise, object
     must return an  array  of  FLONUMs.    The  values  in  these  arrays  are
     concatenated  to  form  the  samples  of the resulting sound.  There is no
     provision for object to specify the logical stop time of the sound, so the
     logical stop time is the termination time.

(snd-fromobjectt0 sr object)
     Creates a sound for which samples come from object. The starting  time  is
     t0  (a  FLONUM),  and the sample rate is sr. The object is an XLISP object
     (see Section IV.11 for information on objects. A sound is returned.   When
     the  sound  needs samples, they are generated by sending the message :next
     to object. If object returns NIL, the sound terminates. Otherwise,  object
     must  return  a  FLONUM.   There is no provision for object to specify the
     logical stop  time  of  the  sound,  so  the  logical  stop  time  is  the
     termination time.

(snd-extent sound maxsamples)
     Returns a list of  two  numbers:  the  starting  time  of  sound  and  the
     terminate time of sound.  Finding the terminate time requires that samples
     be computed.  Like most Nyquist functions,  this  is  non-destructive,  so
     memory  will  be allocated to preserve the sound samples.  If the sound is
     very long or infinite, this may exhaust  all  memory,  so  the  maxsamples
     parameter specifies a limit on how many samples to compute.  If this limit
     is reached, the terminate time will be (incorrectly) based  on  the  sound
     having maxsamples samples.  This function is safe for ordinary use.

(snd-fetch sound)
     Reads samples sequentially from sound. This returns a  FLONUM  after  each
     call,  or NIL when sound terminates. Note: snd-fetch modifies sound; it is
     strongly recommended to copy sound using snd-copy and access only the copy
     with snd-fetch.

(snd-fetch-array sound len step)
     Reads sequential arrays of samples from sound, returning either  an  array
     of  FLONUMs or NIL when the sound terminates. The len parameter, a FIXNUM,
     indicates how many samples should be returned in the result array.   After
     the  array is returned, sound is modified by skipping over step (a FIXNUM)
     samples. If step equals len, then every sample is returned once.  If  step
     is  less  than  len, each returned array will overlap the previous one, so
     some samples will be returned more than once. If step is greater than len,
     then  some samples will be skipped and not returned in any array. The step
     and len may change at each call, but in  the  current  implementation,  an
     internal  buffer  is  allocated for sound on the first call, so subsequent
     calls may not specify a greater len than the first. Note:  snd-fetch-array
     modifies  sound;  it  is strongly recommended to copy sound using snd-copy
     and access only the copy with snd-fetch-array.

(snd-flatten sound maxlen)
     This  function  is identical to snd-length. You would use this function to
     force samples to be computed in memory. Normally, this is not a good thing
     to do, but here is one appropriate use: In the case of sounds intended for
     wavetables, the unevaluated sound may be larger than  the  evaluated  (and
     typically  short)  one.   Calling snd-flatten will compute the samples and
     allow the unit generators to be freed  in  the  next  garbage  collection.
     Note:  If  a  sound  is  computed  from  many  instances  of  table-lookup
     oscillators, calling snd-flatten  will  free  the  oscillators  and  their
     tables.  Calling  (stats)  will  print  how  many  total  bytes  have been
     allocated to tables.

(snd-length sound maxlen)
     Counts  the  number  of samples in sound up to the physical stop time.  If
     the sound has more than maxlen samples, maxlen is returned.  Calling  this
     function  will  cause all samples of the sound to be computed and saved in
     memory (about 4 bytes per sample).  Otherwise, this function is  safe  for
     ordinary use.

(snd-maxsamp sound)
     Computes the maximum of the  absolute  value  of  the  samples  in  sound.
     Calling  this  function  will  cause  samples  to be computed and saved in
     memory.    (This  function  should  have  a  maxlen  parameter  to   allow
     self-defense   against   sounds  that  would  exhaust  available  memory.)
     Otherwise, this function is safe for ordinary use.    This  function  will
     probably  be  removed in a future version.  See peak, a replacement ( page
     21).

(snd-play expression)
     Evaluates expression to obtain a sound or array of sounds, computes all of
     the samples (without retaining them in memory),  and  returns.    If  this
     happens  faster  than  real time for interesting sounds, you might want to
     modify Nyquist to actually write the samples directly to an  audio  output
     device.  Meanwhile, since this function does not save samples in memory or
     write them to a disk, it is useful in determining how much time  is  spent
     calculating  samples.    See  s-save (Section 5.5) for saving samples to a
     file, and play (Section 5.5) to play a sound.  This function is  safe  for
     ordinary use.

(snd-print-tree sound)
     Prints  an  ascii  representation  of   the   internal   data   structures
     representing  a  sound.    This  is  useful  for  debugging Nyquist.  This
     function is safe for ordinary use.

(snd-samples sound limit)
     Converts  the  samples into a lisp array.  The data is taken directly from
     the samples, ignoring shifts.  For example, if the  sound  starts  at  3.0
     seconds, the first sample will refer to time 3.0, not time 0.0.  A maximum
     of limit samples is returned.  This function is safe for ordinary use, but
     like  snd-from-array,  it  requires  a total of slightly over 18 bytes per
     sample.

(snd-srate sound)
     Returns the sample rate of the sound. Safe for ordinary use.

(snd-time sound)
     Returns the start time of the sound.  This will  probably  go  away  in  a
     future version, so use snd-t0 instead.

(snd-t0 sound)
     Returns the time of the first sample of the  sound.    Note  that  Nyquist
     operators  such  as add always copy the sound and are allowed to shift the
     copy up to one half sample period in either direction to align the samples
     of two operands.  Safe for ordinary use.

(snd-print expression maxlen)
     Evaluates expression to yield a sound or an array of sounds,  then  prints
     up to maxlen samples to the screen (stdout).  This is similar to snd-save,
     but samples appear in text on the screen instead of in binary in  a  file.
     This function is intended for debugging.  Safe for ordinary use.

(snd-set-logical-stop sound time)
     Returns a sound which is sound, except that the logical stop of the  sound
     occurs  at  time.    Note:  do  not  call  this function.  When defining a
     behavior, use set-logical-stop or set-logical-stop-abs instead.

(snd-sref sound time)
     Evaluates  sound at the global time given by time.  Safe for ordinary use,
     but normally, you should call sref instead.

(snd-stop-time sound)
     Returns the stop time of sound.  Sounds can be ``clipped'' or truncated at
     a particular time.  This function returns that time or MAX-STOP-TIME if he
     programmer has not specified a stop time for the sound.  Safe for ordinary
     use.

(soundp sound)
     Returns true iff sound is a SOUND.  Safe for ordinary use.

(stats)
     Prints the memory usage status.  See also the XLISP mem  function.    Safe
     for  ordinary  use.  This  is  the only way to find out how much memory is
     being used by table-lookup oscillator instances.



5.1.4. Miscellaneous Functions
  These are all safe and recommended for ordinary use.

(db-to-linear x)
     Returns  the conversion of x from decibels to linear.  0dB is converted to
     1.  20dB represents a linear factor of 10. If x is a sound, each sample is
     converted  and  a  sound  is returned.  If x is a multichannel sound, each
     channel is converted and a multichannel sound (array) is returned.   Note:
     With  sounds,  conversion  is only performed on actual samples, not on the
     implicit zeros before the beginning  and  after  the  termination  of  the
     sound.  Sample rates, start times, etc. are taken from x.

(follow sound floor risetime falltime lookahead)
     An envelope follower intended as a commponent for compressor  and  limiter
     functions.  The basic goal of this function is to generate a smooth signal
     that rides on the peaks of the input signal. The  usual  objective  is  to
     produce  an  amplitude  envelope  given  a  low-sample rate (control rate)
     signal representing local RMS measurements.  The  first  argument  is  the
     input  signal.  The floor is the minimum output value. The risetime is the
     time (in seconds) it takes for the output  to  rise  (exponentially)  from
     floor  to unity (1.0) and the falltime is the time it takes for the output
     to fall (exponentially) from unity to floor. The algorithm looks ahead for
     peaks  and  will begin to increase the output signal according to risetime
     in anticipation of a peak. The amount  of  anticipation  (in  seconds)  is
     given  by  lookahead.    The  algorithm is as follows: the output value is
     allowed to  increase  according  to  risetime  or  decrease  according  to
     falltime. If the next input sample is in this range, that sample is simply
     output as the next output sample.  If the next input sample is too  large,
     the algorithm goes back in time as far as necessary to compute an envelope
     that rises according to risetime to meet the new value. The algorithm will
     only  work  backward as far as lookahead.  If that is not far enough, then
     there is a final forward pass computing a rising signal from the  earliest
     output  sample.  In  this  case,  the  output  signal  will  be  at  least
     momentarily  less  than  the  input  signal  and  will  continue  to  rise
     exponentially  until  it  intersects the input signal. If the input signal
     falls faster than indicated by falltime, the  output  fall  rate  will  be
     limited  by  falltime,  and  the  fall in output will stop when the output
     reaches floor.  This algorithm can make two passes througth the buffer  on
     sharply  rising inputs, so it is not particularly fast. With short buffers
     and low sample rates this should not matter. See snd-avg  for  a  function
     that  can  help  to  generate  a  low-sample-rate  input  for follow.  See
     snd-chase in Section 5.6.3 for a related filter.

(gate sound floor risetime falltime lookahead threshold)
     Generate   an   exponential   rise  and  decay  intended  for  noise  gate
     implementation. The decay starts when the signal drops below threshold and
     stays  there  for longer than lookahead (a FLONUM in seconds). (The signal
     begins to drop when the signal crosses threshold,  not  after  lookahead.)
     Decay  continues  until the value reaches floor (a FLONUM), at which point
     the decay stops and the output value is held constant. Either  during  the
     decay  or  after the floor is reached, if the signal goes above threshold,
     then the ouptut value will rise to unity (1.0) at  the  point  the  signal
     crosses  the threshold. Because of internal lookahead, the signal actually
     begins to rise  before  the  signal  crosses  threshold.  The  rise  is  a
     constant-rate  exponential  and  set  so  that  a rise from floor to unity
     occurs in risetime. Similary, the fall is a constant-rate exponential such
     that a fall from unity to floor takes falltime.

(hz-to-step freq)
     Returns a step number for freq (in hz), which can be either a number of  a
     SOUND.  The  result has the same type as the argument. See also step-to-hz
     (below).

(linear-to-db x)
     Returns the conversion of x from linear to decibels.  1 is converted to 0.
     0 is converted to -INF (a special IEEE floating point value.)  A factor of
     10  represents  a  20dB change.  If x is a sound, each sample is converted
     and a sound is returned.  If x is a multichannel sound,  each  channel  is
     converted  and  a  multichannel  sound  (array)  is  returned.  Note: With
     sounds, conversion is  only  performed  on  actual  samples,  not  on  the
     implicit  zeros  before  the  beginning  and  after the termination of the
     sound.  Start times, sample rates, etc. are taken from x.

(log x)
     Calculates  the natural log of x (a FLONUM). (See s-log for a version that
     operates on signals.)

(set-control-srate rate)
     Sets  the  default  sampling  rate  for control signals to rate by setting
     *default-control-srate* and reinitializing the environment.  Do  not  call
     this   within   any   synthesis   function   (see   the  control-srate-abs
     transformation, Section 5.3).

(set-sound-srate rate)
     Sets  the  default  sampling  rate  for  audio  signals to rate by setting
     *default-sound-srate* and reinitializing the environment.    Do  not  call
     this    within   any   synthesis   function   (see   the   sound-srate-abs
     transformation, Section 5.3).

(set-pitch-names)
     Initializes  pitch variables (c0, cs0, df0, d0, ... b0, c1, ... b7).  A440
     (the default tuning) is represented by the step 69.0, so the  variable  a4
     (fourth  octave  A)  is set to 69.0.  You can change the tuning by setting
     *A4-Hertz*  to  a  value  (in  Hertz)  and  calling   set-pitch-names   to
     reinitialize  the  pitch  variables.    Note  that  this  will  result  in
     non-integer step values.  It does not alter the mapping from  step  values
     to  frequency.    There  is  no built-in provision for stretched scales or
     non-equal temperament, although users can write  or  compute  any  desired
     fractional step values.

(step-to-hz pitch)
     Returns a frequency in hz for  pitch,  a  step  number  or  a  SOUND  type
     representing  a  time-varying step number. The result is a FLONUM if pitch
     is a number, and a SOUND if pitch is a SOUND. See also hz-to-step (above).

(get-duration dur)
     Gets the actual duration of of something starting at a local time of 0 and
     ending at a local time of dur times the current sustain. For  convenience,
     *rslt* is set to the global time corresponding to local time zero.

(get-loud)
     Gets the current value of the *loud* environment variable.  If *loud* is a
     signal, it is evaluated at local time 0 and a number (FLONUM) is returned.

(get-sustain)
     Gets the  current  value  of  the  *sustain*  environment  variable.    If
     *sustain*  is  a  signal,  it  is  evaluated  at local time 0 and a number
     (FLONUM) is returned.

(get-transpose)
     Gets  the  current  value  of  the  *transpose*  environment variable.  If
     *transpose* is a signal, it is evaluated at local  time  0  and  a  number
     (FLONUM) is returned.

(get-warp)
     Gets  a  function  corresponding  to  the  current  value  of  the  *warp*
     environment  variable.    For  efficiency, *warp* is stored in three parts
     representing a shift, a scale factor,  and  a  continuous  warp  function.
     Get-warp is used to retrieve a signal that maps logical time to real time.
     This signal combines the information of all  three  components  of  *warp*
     into  a  single  signal.  If the continuous warp function component is not
     present (indicating that the time warp is a simple combination of  at  and
     stretch transformations), an error is raised.  This function is mainly for
     internal  system  use.    In  the  future,  get-warp  will   probably   be
     reimplemented to always return a signal and never raise an error.

(local-to-global local-time)
     Converts a score (local) time to a real (global)  time  according  to  the
     current environment.

(osc-enable flag)
     Enable or disable Open Sound Control. (See Appendix II.)  Enabling creates
     a  socket  and  a  service  that  listens  for  UDP  packets on port 7770.
     Currently, only messages of the form \slider with an integer index  and  a
     floating  point  value  are  accepted.  These  set  internal slider values
     accessed by the snd-slider  function.  Disabling  terminates  the  service
     (polling  for  messages)  and  closes  the  socket.  The previous state of
     enablement is returned, e.g. if OSC is enabled and flag  is  nil,  OSC  is
     disabled  and  T (true) is returned because OSC was enabled at the time of
     the call. This function only  exists  if  Nyquist  is  compiled  with  the
     compiler  flag  OSC. Otherwise, the function exists but always returns the
     symbol DISABLED.  Consider  lowering  the  audio  latency  using  snd-set-
     latency.   Warning: there is the potential for network-based attacks using
     OSC. It is tempting to add the ability to evaluate XLISP expressions  sent
     via  OSC,  but  this  would create unlimited and unprotected access to OSC
     clients. For now, it is unlikely that  an  attacker  could  do  more  than
     manipulate slider values.

(snd-set-latency latency)
     Set the latency requested when Nyquist plays sound to latency,  a  FLONUM.
     The  previous  value  is  returned.  The  default is 0.3 seconds. To avoid
     glitches, the latency should be greater than the time required for garbage
     collection  and message printing and any other system activity external to
     Nyquist.

5.2. Behaviors



5.2.1. Using Previously Created Sounds
  These behaviors take a sound  and  transform  that  sound  according  to  the
environment.   These are useful when writing code to make a high-level function
from a low-level function, or when cuing sounds which were previously created:

(cue sound)
     Applies  *loud*,  the  starting  time  from *warp*, *start*, and *stop* to
     sound.

(cue-file filename)
     Same  as  cue,  except  the  sound comes from the named file, samples from
     which are coerced to the current default *sound-srate* sample rate.

(sound sound)
     Applies *loud*, *warp*, *start*, and *stop* to sound.

(control sound)
     This function is identical to sound, but by convention is used when  sound
     is a control signal rather than an audio signal.



5.2.2. Sound Synthesis
  These  functions  provide musically interesting creation behaviors that react
to their environment; these are the ``unit generators'' of Nyquist:

(const value [duration])
     Creates  a constant function at the *control-srate*.  Every sample has the
     given value, and the default duration is 1.0.  See also s-rest,  which  is
     equivalent  to  calling const with zero, and note that you can pass scalar
     constants (numbers) to sim, sum, and mult  where  they  are  handled  more
     efficiently than constant functions.

(env t  t  t  l  l  l  [dur])
      1  2  4  1  2  3
     Creates a 4-phase envelope.  t  is the duration of phase i, and l  is  the
                                   i                                  i
     final level of phase i.  t  is implied by the duration dur, and l  is 0.0.
                               3                                      4
     If dur is not supplied, then 1.0 is assumed.  The envelope duration is the
     product  of  dur,  *stretch*,  and  *sustain*.    If t  + t  + 2ms + t  is
                                                           1    2          4
     greater  than  the  envelope  duration,  then  a  two-phase  envelope   is
     substituted  that  has  an attack/release time ratio of t /t .  The sample
                                                              1  4
     rate of the returned sound is  *control-srate*.    (See  pwl  for  a  more
     general piece-wise linear function generator.)  The effect of time warping
     is  to  warp  the  starting  time  and  ending  time.    The  intermediate
     breakpoints are then computed as described above.

(exp-dec hold halfdec length)
     This convenient envelope shape is a special  case  of  pwev  (see  Section
     5.2.2.2).  The  envelope  starts at 1 and is constant for hold seconds. It
     then decays with a half life of halfdec seconds until length.  (The  total
     duration  is  length.)  In  other  words, the amplitude falls by half each
     halfdec seconds. When stretched,  this  envelope  scales  linearly,  which
     means the hold time increases and the half decay time increases.

(force-srate srate sound)
     Returns a sound which is up- or down-sampled to srate.   Interpolation  is
     linear,  and  no  prefiltering  is  applied  in  the  down-sample case, so
     aliasing may occur. See also resample.

(lfo freq [duration table phase])
     Just  like  osc  (below)  except  this computes at the *control-srate* and
     frequency is specified in Hz.    Phase  is  specified  in  degrees.    The
     *transpose*  and  *sustain* is not applied.  The effect of time warping is
     to warp the starting and ending times.  The  signal  itself  will  have  a
     constant unwarped frequency.

(fmlfo freq [table phase])
     A low-frequency oscillator that computes at the  *control-srate*  using  a
     sound  to  specify  a  time-varying  frequency in Hz. Phase is a FLONUM in
     degrees. The duration of the result is determined by freq.

(maketable sound)
     Assumes  that  the  samples in sound constitute one period of a wavetable,
     and returns a wavetable suitable for use as the table argument to the  osc
     function (see below).  Currently, tables are limited to 1,000,000 samples.
     This limit is the compile-time constant max_table_len set in sound.h.

(build-harmonic n table-size)
     Intended  for  constructing  wavetables,  this function returns a sound of
     length table-size samples containing n periods of a sinusoid.   These  can
     be scaled and summed to form a waveform with the desired harmonic content.
     See page 2 for an example.

(clarinet step breath-env)
     A  physical  model  of a clarinet from STK. The step parameter is a FLONUM
     that controls the tube length, and the breath-env (a SOUND)  controls  the
     air  pressure  and  also determines the length of the resulting sound. The
     breath-env signal should range from zero to one.

(clarinet-freqstep breath-env freq-env)
     A  variation  of  clarinet  that  includes  a  variable frequency control,
     freq-env, which specifies frequency deviation in Hz. The duration  of  the
     resulting  sound is the minimum duration of breath-env and freq-env. These
     parameters may be of type FLONUM or SOUND. FLONUMs are coerced into SOUNDs
     with a nominal duration arbitrarily set to 30.

(clarinet-allstep  breath-env freq-env vibrato-freq vibrato-gain reed-stiffness
     noise)
     A variation of clarinet-freq that includes controls vibrato-freq (a FLONUM
     for vibrato frequency in Hertz), vibrato-gain (a FLONUM for the amount  of
     amplitude  vibrato),  reed-stiffness  (a  FLONUM or SOUND controlling reed
     stiffness in the clarinet model), and noise (a FLONUM or SOUND controlling
     noise  amplitude  in the input air pressure). The vibrato-gain is a number
     from zero to one, where zero indicates no vibrato,  and  one  indicates  a
     plus/minus  50%  change  in  breath  envelope values. Similarly, the noise
     parameter ranges from zero to one where zero means no noise and one  means
     white noise with a peak amplitude of plus/minus 40% of the breath-env. The
     reed-stiffness parameter varies from zero to one.   The  duration  of  the
     resulting   sound   is  the  minimum  duration  of  breath-env,  freq-env,
     reed-stiffness, and noise. As with clarinet-freq, these parameters may  be
     either FLONUMs or SOUNDs, and FLONUMs are coerced to sounds with a nominal
     duration of 30.

(control-warp warp-fn signal [wrate])
     Applies  a warp function warp-fn to signal using function composition.  If
     wrate is omitted, linear interpolation is used.  warp-fn is a mapping from
     score  (logical)  time  to  real time, and signal is a function from score
     time to real values.  The result is a function  from  real  time  to  real
     values  at  a  sample  rate  of  *control-srate*.  See  sound-warp  for an
     explanation of wrate and high-quality warping.

(mult beh  beh  ...)
         1    2
     Returns  the  product of behaviors.  The arguments may also be numbers, in
     which case simple multiplication is performed.  If a number and sound  are
     mixed,  the  scale function is used to scale the sound by the number. When
     sounds are multiplied, the resulting sample rate  is  the  maximum  sample
     rate of the factors.

(prod beh  beh  ...)
         1    2
     Same as mult.

(pan sound where)
     Pans sound (a behavior) according to where (another behavior or a number).
     Sound must be monophonic. Where may be a monophonic sound (e.g. (ramp)  or
     simply  a  number (e.g. 0.5). In either case, where should range from 0 to
     1, where 0 means pan completely left, and 1 means  pan  completely  right.
     For  intermediate  values,  the  sound to each channel is scaled linearly.
     Presently, pan does not check its arguments carefully.

(prod beh  beh  ...)
         1    2
     Same as mult.

(resample sound srate)
     Similar to force-srate,  except  high-quality  interpolation  is  used  to
     prefilter  and  reconstruct  the  signal at the new sample rate. Also, the
     result is scaled by 0.95 to  reduce  problems  with  clipping.  (See  also
     sound-warp.)

(sax step breath-env)
     A physical model of a sax from STK. The step parameter is  a  FLONUM  that
     controls the tube length, and the breath-env controls the air pressure and
     also determines the length of the resulting sound. The  breath-env  signal
     should range from zero to one.

(sax-freqstep breath-env freq-env)
     A variation of sax that includes a variable frequency  control,  freq-env,
     which  specifies  frequency deviation in Hz. The duration of the resulting
     sound is the minimum duration of breath-env and freq-env. These parameters
     may  be  of  type  FLONUM or SOUND. FLONUMs are coerced into SOUNDs with a
     nominal duration arbitrarily set to 30.

(sax-allstep breath-env freq-env vibrato-freq vibrato-gain reed-stiffness noise
     blow-pos reed-table-offset)
     A variation of sax-freq that includes controls vibrato-freq (a FLONUM  for
     vibrato  frequency  in  Hertz),  vibrato-gain  (a FLONUM for the amount of
     amplitude vibrato), reed-stiffness (a SOUND controlling reed stiffness  in
     the  sax  model),  noise (a SOUND controlling noise amplitude in the input
     air pressure), blow-pos (a SOUND controlling the point  of  excitation  of
     the air column), and reed-table-offset (a SOUND controlling a parameter of
     the reed model). The vibrato-gain is a number from zero to one, where zero
     indicates  no vibrato, and one indicates a plus/minus 50% change in breath
     envelope values. Similarly, the noise parameter ranges from  zero  to  one
     where  zero means no noise and one means white noise with a peak amplitude
     of plus/minus 40% of the breath-env.  The  reed-stiffness,  blow-pos,  and
     reed-table-offset  parameters  all vary from zero to one.  The duration of
     the resulting sound is  the  minimum  duration  of  breath-env,  freq-env,
     reed-stiffness,  noise,  breath-env,  blow-pos,  and reed-table-offset. As
     with sax-freq, these parameters may  be  either  FLONUMs  or  SOUNDs,  and
     FLONUMs are coerced to sounds with a nominal duration of 30.

(scale scale sound)
     Scales the amplitude of sound by the factor scale.  Identical function  to
     snd-scale,  except  that  it  handles  multichannel sounds.  Sample rates,
     start times, etc. are taken from sound.

(scale-db db sound)
     Scales  the  amplitude  of  sound by the factor db, expressed in decibels.
     Sample rates, start times, etc. are taken from sound.

(scale-srate sound scale)
     Scales  the  sample rate of sound by scale factor.  This has the effect of
     linearly shrinking or stretching time  (the  sound  is  not  upsampled  or
     downsampled).  This is a special case of snd-xform (see Section 5.6.2).

(shift-time sound shift)
     Shift sound by shift seconds.  If the sound is f(t), then  the  result  is
     f(t-shift).    See  Figure  5.    This is a special case of snd-xform (see
     Section 5.6.2).





















     Figure 5:  The shift-time function shifts a sound in time   according
     to its shift argument.


(sound-warp warp-fn signal [wrate])
     Applies a warp function warp-fn to signal using function composition.   If
     the  optional  parameter  wrate is omitted or NIL, linear interpolation is
     used.  Otherwise, high-quality  sample  interpolation  is  used,  and  the
     result  is  scaled  by 0.95 to reduce problems with clipping (interpolated
     samples can exceed the peak values of the input samples.)   warp-fn  is  a
     mapping  from  score (logical) time to real time, and signal is a function
     from score time to real values.  The result is a function from  real  time
     to real values at a sample rate of *sound-srate*.  See also control-warp.

     If  wrate  is  not  NIL, it must be a number. The parameter indicates that
     high-quality resampling should be used and specifies the sample  rate  for
     the  inverse  of  warp-fn.  Use the lowest number you can.  (See below for
     details.) Note that high-quality resampling is  much  slower  than  linear
     interpolation.

     To  perform  high-quality  resampling  by  a  fixed ratio, as opposed to a
     variable ratio allowed in sound-warp, use scale-srate to stretch or shrink
     the sound, and then resample to restore the original sample rate.

     Sound-warp  and  control-warp  both  take  the inverse of warp-fn to get a
     function from real time to score time. Each sample of this inverse is thus
     a  score time; signal is evaluated at each of these score times to yield a
     value, which is the desired result. The sample rate of  the  inverse  warp
     function  is  somewhat  arbitrary.  With linear interpolation, the inverse
     warp function sample rate is taken to be the  output  sample  rate.  Note,
     however,  that  the  samples  of  the  inverse warp function are stored as
     32-bit  floats,  so  they  have  limited  precision.  Since  these  floats
     represent  sample  times, rounding can be a problem. Rounding in this case
     is equivalent to adding jitter to the sample times. Nyquist  ignores  this
     problem  for  ordinary  warping,  but for high-quality warping, the jitter
     cannot be ignored.

     The solution is to use a rather low  sample  rate  for  the  inverse  warp
     function.  Sound-warp  can  then  linearly  interpolate  this signal using
     double-precision floats to minimize jitter  between  samples.  The  sample
     rate  is  a  compromise:  a low sample rate minimizes jitter, while a high
     sample  rate  does  a  better  job  of  capturing   detail   (e.g.   rapid
     fluctuations) in the warp function. A good rule of thumb is to use at most
     1,000 to 10,000 samples for the inverse warp function. For example, if the
     result  will  be 1 minute of sound, use a sample rate of 3000 samples / 60
     seconds = 50 samples/second. Because Nyquist has  no  advance  information
     about  the  warp  function,  the inverse warp function sample rate must be
     provided as a parameter.  When in doubt, just try something and  let  your
     ears be the judge.

(integrate signal)
     Computes the integral of signal. The start time,  sample  rate,  etc.  are
     taken from signal.

(slope signal)
     Computes the first derivative (slope) of signal.  The start  time,  sample
     rate, etc. are taken from signal.


5.2.2.1. Oscillators

(osc pitch [duration table phase])
     Returns a sound which is the table  oscillated  at  pitch  for  the  given
     duration,  starting  with the phase (in degrees).  Defaults are:  duration
     1.0 (second), table *table*, phase 0.0.  The default value of *table* is a
     sinusoid.  Duration  is  stretched  by  *warp* and *sustain*, amplitude is
     nominally 1, but scaled by *loudness*, the start time is logical  time  0,
     transformed  by  *warp*, and the sample rate is *sound-srate*.  The effect
     of time-warping is to warp the starting and ending times only; the  signal
     has a constant unwarped frequency.  Note 1: table is a list of the form

         (sound pitch-number periodic)

     where  the  first element is a sound, the second is the pitch of the sound
     (this is not redundant, because the sound  may  represent  any  number  of
     periods),  and  the  third  element  is  T if the sound is one period of a
     periodic signal, or nil if the sound  is  a  sample  that  should  not  be
     looped.  The maximum table size is set by max_table_len in sound.h, and is
     currently set to 1,000,000.  Note 2: in the current implementation, it  is
     assumed  that  the output should be periodic.  See snd-down and snd-up for
     resampling one-shot sounds to a desired sample rate.  A future version  of
     osc  will  handle  both  cases.    Note  3:  When osc is called, memory is
     allocated for the table, and samples are copied from the sound (the  first
     element  of  the  list which is the table parameter) to the memory.  Every
     instance of osc has a private copy of the table, so the total storage  can
     become  large  in  some cases, for example in granular synthesis with many
     instances of osc. In some cases, it may make sense to use snd-flatten (see
     Section  5.1.3)  to  cause the sound to be fully realized, after which the
     osc and its table memory can  be  reclaimed  by  garbage  collection.  The
     partial  function  (see  below) does not need a private table and does not
     use much space.

(partial pitch env)
     Returns a sinusoid at the indicated pitch; the sound is multiplied by env.
     The start time and duration are taken from env, which is of course subject
     to  transformations.    The  sample  rate  is  *sound-srate*.  The partial
     function is faster than osc.

(sine pitch [duration])
     Returns   a  sinusoid  at  the  indicated  pitch.    The  sample  rate  is
     *sound-srate*.  This function is like osc with respect to transformations.
     The sine function is faster than osc.

(hzosc hz [table phase])
     Returns a sound which is the table oscillated  at  hz  starting  at  phase
     degrees.  The  default  table is *table* and the default phase is 0.0. The
     default duration is 1.0, but this is stretched as in osc (see above).  The
     hz  parameter  may be a SOUND, in which case the duration of the result is
     the duration of hz. The sample rate is *sound-srate*.

(osc-saw hz)
     Returns  a  sawtooth  waveshape at the indicated frequency (in Hertz). The
     sample rate is *sound-srate*. The hz parameter may be a sound as in  hzosc
     (see above).

(osc-tri hz)
     Returns a triangle waveshape at the indicated frequency  (in  Hertz).  The
     sample  rate is *sound-srate*. The hz parameter may be a sound as in hzosc
     (see above).

(osc-pulse hz bias [compare-shape])
     Returns  a square pulse with variable width at the indicated frequency (in
     Hertz). The bias parameter controls the pulse width and should be  between
     -1  and +1, giving a pulse width from 0% (always at -1) to 100% (always at
     +1). When bias is zero, a square wave is generated. Bias may be a SOUND to
     create  varying  pulse width. If bias changes rapidly, strange effects may
     occur. The optional compare-shape defaults to a hard  step  at  zero,  but
     other  shapes  may  be  used  to  achieve non-square pulses. The osc-pulse
     behavior is written in terms of other behaviors and defined  in  the  file
     nyquist.lsp using just a few lines of code. Read the code for the complete
     story.

(amosc pitch modulation [table phase])
     Returns  a  sound  which  is  table  oscillated  at  pitch.  The output is
     multiplied by  modulation  for  the  duration  of  the  sound  modulation.
     osc-table  defaults  to  *table*, and phase is the starting phase (default
     0.0 degrees) within osc-table.  The sample rate is *sound-srate*.

(fmosc pitch modulation [table phase])
     Returns a sound which is table oscillated at pitch plus modulation for the
     duration of the sound modulation.   osc-table  defaults  to  *table*,  and
     phase  is  the starting phase (default 0.0 degrees) within osc-table.  The
     modulation is expressed in hz, e.g. a sinusoid modulation signal  with  an
     amplitude  of  1.0  (2.0  peak to peak), will cause a +/N 1.0 hz frequency
     deviation in sound.  Negative frequencies  are  correctly  handled.    The
     sample rate is *sound-srate*.

(buzz n pitch modulation)
     Returns a sound with n harmonics of equal amplitude and a total  amplitude
     of  1.0,  using a well-known function of two cosines. If n (an integer) is
     less than 1, it is set to 1. Aliasing will occur if n is too large.    The
     duration is determined by the duration of the sound modulation, which is a
     frequency modulation term expressed in Hz (see Section 5.2.2.1).  Negative
     frequencies are correctly handled.  The sample rate is *sound-srate*.

(pluck pitch [duration] [final-amplitude])
     Returns a sound at the given pitch created using a modified Karplus-Strong
     plucked  string  algorithm. The tone decays from an amplitude of about 1.0
     to about final-amplitude in duration seconds. The default  values  are  to
     decay to 0.001 (-60dB) in 1 second. The sample rate is *sound-srate*.

(siosc pitch modulation tables)
     Returns a sound constructed  by  interpolating  through  a  succession  of
     periodic  waveforms.  The  frequency  is given (in half steps) by pitch to
     which a modulation signal (in hz) is  added,  exactly  as  in  fmosc.  The
     tables  specify  a  list of waveforms as follows: (table0 time1 table2 ...
     timeN tableN), where each table is a sound representing one  period.  Each
     time  is  a  time  interval  measured  from the starting time. The time is
     scaled  by  the  nominal   duration   (computed   using   (local-to-global
     (get-sustain)))  to  get  the  actual  time. Note that this implies linear
     stretching rather than continuous timewarping of the interpolation or  the
     breakpoints.  The  waveform  is  table0 at the starting time, table1 after
     time1 (scaled as described), and so on. The duration and logical stop time
     is given by modulation. If modulation is shorter than timeN, then the full
     sequence of waveforms is not used.  If modulation is  longer  than  timeN,
     tableN is used after timeN without further interpolation.

(sampler pitch modulation [sample npoints])
     Returns a sound constructed by reading a sample from beginning to end  and
     then  splicing  on  copies of the same sound from a loop point to the end.
     The pitch and modulation parameters are used as in fmosc described  above.
     The  optional  sample  (which defaults to the global variable *table* is a
     list of the form

         (sound pitch-number loop-start)

     where the first element is a sound containing the sample,  the  second  is
     the  pitch  of  the  sample, and the third element is the time of the loop
     point. If the loop point is not in the bounds of the sound, it is  set  to
     zero.    The optional npoints specifies how many points should be used for
     sample interpolation.  Currently this parameter defaults  to  2  and  only
     2-point (linear) interpolation is implemented.  It is an error to modulate
     such that the frequency is negative. Note also that the loop point may  be
     fractional.  The sample rate is *sound-srate*.


5.2.2.2. Piece-wise Approximations
  There  are  a  number  of  related behaviors for piece-wise approximations to
functions.  The simplest of these, pwl was mentioned earlier in the manual.  It
takes  a  list of breakpoints, assuming an initial point at (0, 0), and a final
value of 0.  An analogous piece-wise exponential function,  pwe,  is  provided.
Its  implicit  starting and stopping values are 1 rather than 0.  Each of these
has variants.  You can specify the initial and final values (instead of  taking
the  default).  You can specify time in intervals rather than cummulative time.
Finally, you can pass a list rather than an argument list.  This  leads  to  16
versions:

    Piece-wise Linear Functions:
        Cummulative Time:
            Default initial point at (0, 0), final value at 0:
                pwl
                pwl-list
            Explicit initial value:
                pwlv
                pwlv-list
        Relative Time:
            Default initial point at (0, 0), final value at 0:
                pwlr
                pwlr-list
            Explicit initial value:
                pwlvr
                pwlvr-list
    Piece-wise Exponential Functions:
        Cummulative Time:
            Default initial point at (0, 1), final value at 1:
                pwe
                pwe-list
            Explicit initial value:
                pwev
                pwev-list
        Relative Time:
            Default initial point at (0, 1), final value at 1:
                pwer
                pwer-list
            Explicit initial value:
                pwevr
                pwevr-list

All of these functions are implemented in terms of pwl (see nyquist.lsp for the
implementations.    There  are  infinite  opportunities  for  errors  in  these
functions:  if  you  leave  off  a data point, try to specify points in reverse
order, try to create an exponential that goes to zero or  negative  values,  or
many  other  bad  things, the behavior is not well-defined.  Nyquist should not
crash, but Nyquist does not necessarily attempt to report errors at this time.

(pwl t  l  t  l  ... t )
      1  1  2  2      n
     Creates a piece-wise linear envelope with breakpoints at (0, 0), (t , l ),
                                                                        1   1
     (t , l ), ... (t , 0).  The breakpoint times are scaled  linearly  by  the
       2   2         n
     value  of  *sustain* (if *sustain* is a SOUND, it is evaluated once at the
     starting time of the envelope).   Each  breakpoint  time  is  then  mapped
     according  to  *warp*.    The  result is a linear interpolation (unwarped)
     between the breakpoints.  The sample rate is *control-srate*.   Breakpoint
     times  are  quantized  to  the nearest sample time.  If you specify one or
     more breakpoints withing one sample period, pwl attempts to  give  a  good
     approximation   to   the  specified  function.    In  particular,  if  two
     breakpoints are simultaneous, pwl will move one of  them  to  an  adjacent
     sample,  producing  a  steepest  possible  step  in the signal.  The exact
     details of this ``breakpoint munging'' is  subject  to  change  in  future
     versions.   Please report any cases where breakpoint lists give unexpected
     behaviors.  The  author  will  try  to  apply  the  ``principle  of  least
     surprise'' to the design.  Note that the times are relative to 0; they are
     not durations of each envelope segment.

(pwl-list breakpoints)
     If  you  have  a  list  of breakpoints, you can use apply to apply the pwl
     function to the breakpoints, but if the list is  very  long  (hundreds  or
     thousands  of  points), you might get a stack overflow because XLISP has a
     fixed-size argument stack.  Instead, call pwl-list, passing one  argument,
     the list of breakpoints.

(pwlv l  t  l  t  t  ... t  l )
       1  2  2  3  3      n  n
     Creates a piece-wise linear envelope with breakpoints  at  (0,  l ),  (t ,
                                                                      1      2
     l ),  etc.,  ending with (t , l .  Otherwise, the behavior is like that of
      2                         n   n
     pwl.

(pwlv-list breakpoints)
     A version of pwlv that takes a single list of breakpoints as its argument.
     See pwl-list above for the rationale.

(pwlr i  l  i  l  ... i )
       1  1  2  2      n
     Creates a piece-wise linear envelope with breakpoints at (0, 0), (t , l ),
                                                                        1   1
     (t , l ), ... (t , 0), where t  is the sum of i  through  i .    In  other
       2   2         n             j                1           j
     words,  the  breakpoint  times  are specified in terms of intervals rather
     than cummulative time.  Otherwise, the behavior is like that of pwl.

(pwlr-list breakpoints)
     A version of pwlr that takes a single list of breakpoints as its argument.
     See pwl-list above for the rationale.

(pwlvr l  i  l  i  i  ... i  l )
        1  2  2  3  3      n  n
     Creates  a  piece-wise  linear  envelope with breakpoints at (0, l ), (t ,
                                                                       1     2
     l ), etc., ending with (t , l , where t  is the sum of i  through i .   In
      2                       n   n         j                2          j
     other  words,  the  breakpoint  times  are specified in terms of intervals
     rather than cummulative time.  Otherwise, the behavior  is  like  that  of
     pwlv.

(pwlvr-list breakpoints)
     A version of pwlvr  that  takes  a  single  list  of  breakpoints  as  its
     argument.  See pwl-list above for the rationale.

(pwe t  l  t  l  ...  t )
      1  1  2  2       n
     Creates a piece-wise exponential envelope with breakpoints at (0, 1), (t ,
                                                                             1
     l ),  (t , l ), ... (t , 1).  Exponential segments means that the ratio of
      1      2   2         n
     values from sample to sample is constant within the segment.  (The current
     implementation actually takes the log of each value, computes a piece-wise
     exponential from the points using pwl, then exponentiates  each  resulting
     sample.    A  faster  implementation  is  certainly possible!)  Breakpoint
     values (l ) must be greater  than  zero.    Otherwise,  this  function  is
              j
     similar  to  pwl,  including  stretch  by  *sustain*, mapping according to
     *warp*, sample rate based on  *control-srate*,  and  "breakpoint  munging"
     (see  pwl  described  above).    Default  initial  and final values are of
     dubious value with exponentials.  See pwev below for the function you  are
     probably looking for.

(pwe-list breakpoints)
     A version of pwe that takes a single list of breakpoints as its  argument.
     See pwl-list above for the rationale.

(pwev l  t  l  t  t  ... t  l )
       1  2  2  3  3      n  n
     Creates a piece-wise exponential envelope with  breakpoints  at  (0,  l ),
                                                                            1
     (t , l ), etc., ending with (t , l .  Otherwise, the behavior is like that
       2   2                       n   n
     of pwe.

(pwev-list breakpoints)
     A version of pwev that takes a single list of breakpoints as its argument.
     See pwl-list above for the rationale.

(pwer i  l  i  l  ... i )
       1  1  2  2      n
     Creates a piece-wise exponential envelope with breakpoints at (0, 1), (t ,
                                                                             1
     l ), (t , l ), ... (t , 1), where t  is the sum of  i   through  i .    In
      1     2   2         n             j                 1            j
     other  words,  the  breakpoint  times  are specified in terms of intervals
     rather than cummulative time.  Otherwise, the behavior  is  like  that  of
     pwe.  Consider using pwerv instead of this one.

(pwer-list breakpoints)
     A version of pwer that takes a single list of breakpoints as its argument.
     See pwl-list above for the rationale.

(pwevr l  i  l  i  i  ... i  l )
        1  2  2  3  3      n  n
     Creates a piece-wise exponential envelope with  breakpoints  at  (0,  l ),
                                                                            1
     (t , l ), etc., ending with (t , l , where t  is the sum of i  through i .
       2   2                       n   n         j                2          j
     In other words, the breakpoint times are specified in terms  of  intervals
     rather  than  cummulative  time.   Otherwise, the behavior is like that of
     pwev.  Note that this is similar to the csound GEN05 generator.  Which  is
     uglier, GEN05 or pwevr?

(pwevr-list breakpoints)
     A version of pwevr  that  takes  a  single  list  of  breakpoints  as  its
     argument.  See pwl-list above for the rationale.


5.2.2.3. Filter Behaviors

(alpass  sound decay hz [minhz])
     Applies an all-pass filter to sound.  This all-pass filter creates a delay
     effect  without  the  resonances  of  a comb filter. The decay time of the
     filter is given by decay.  The hz parameter must  be  a  number  or  sound
     greater  than zero.  It is used to compute delay, which is then rounded to
     the nearest integer number of samples (so  the  frequency  is  not  always
     exact.    Higher sampling rates yield better delay resolution.)  The decay
     may be a sound or a number.  In either case, it  must  also  be  positive.
     (Implementation  note:  an  exponentiation is needed to convert decay into
     the   feedback   parameter,   and   exponentiation   is   typically   more
     time-consuming than the filter operation itself.  To get high performance,
     provide decay at a low sample rate.)  The resulting sound  will  have  the
     start  time, sample rate, etc. of sound. If hz is of type SOUND, the delay
     may be time-varying. Linear interpolation  is  then  used  for  fractional
     sample  delay,  but it should be noted that linear interpolation implies a
     low-pass transfer function. Thus, this filter may behave differently  with
     a  constant SOUND than it does with a FLONUM value for hz. In addition, if
     hz is of type SOUND, then minhz is required.  The  hz  parameter  will  be
     clipped  to  be  greater  than  minhz, placing an upper bound on the delay
     buffer length.

(comb  sound decay hz)
     Applies  a  comb filter to sound.  A comb filter emphasizes (resonates at)
     frequencies that are multiples of a hz. The decay time of the resonance is
     given  by  decay.  This is a variation on feedback-delay (see below).  The
     hz parameter must be a number greater than zero.  It is  used  to  compute
     delay,  which is then rounded to the nearest integer number of samples (so
     the frequency is not always exact.  Higher  sampling  rates  yield  better
     delay resolution.)  The decay may be a sound or a number.  In either case,
     it must also be positive.   (Implementation  note:  an  exponentiation  is
     needed  to  convert  decay into the feedback parameter for feedback-delay,
     and exponentiation  is  typically  more  time-consuming  than  the  filter
     operation  itself.  To get high performance, provide decay at a low sample
     rate.)  The resulting sound will have the start time, sample rate, etc. of
     sound.

(congen gate risetime falltime)
     Implements an analog synthesizer-style contour generator. The  input  gate
     normally  goes  from 0.0 to 1.0 to create an attack and from 1.0 to 0.0 to
     start a release.  During the attack (output  is  increasing),  the  output
     converges  half-way  to  gate  in  risetime (a FLONUM) seconds. During the
     decay, the half-time is falltime seconds. The  sample  rate,  start  time,
     logical  stop,  and  terminate time all come from gate. If you want a nice
     decay, be sure that the gate goes to  zero  and  stays  there  for  awhile
     before  gate  terminates,  because  congen  (and  all  Nyquist  sounds) go
     immediately to zero at termination time.  For example, you can use pwl  to
     build a pulse followed by some zero time:

         (pwl 0 1 duty 1 duty 0 1)

     Assuming  duty  is  less  than  1.0, this will be a pulse of duration duty
     followed by zero for a total duration of 1.0.

         (congen (pwl 0 1 duty 1 duty 0 1) 0.01 0.05)

     will have a duration of 1.0 because that is the termination  time  of  the
     pwl  input.  The  decaying  release  of  the  resulting  envelope  will be
     truncated to zero at time 1.0. (Since the decay is theoretically infinite,
     there  is  no  way  to  avoid  truncation,  although you could multiply by
     another envelope that smoothly truncates to zero in the  last  millisecond
     or  two  to get both an exponential decay and a smooth final transition to
     zero.)

(convolve sound response)
     Convolves  two  signals.  The first can be any length, but the computation
     time per sample and the total  space  required  are  proportional  to  the
     length of response.

(feedback-delay sound delay feedback)
     Applies feedback delay to sound.  The delay must be a number (in seconds).
     It  is rounded to the nearest sample to determine the length of the delay.
     The sample rate is the maximum from sound and  feedback  (if  feedback  is
     also a sound).  The amound of feedback should be less than one to avoid an
     exponential increase in amplitude.  The start  time  and  stop  time,  and
     logical  stop time are taken from sound.  Since output is truncated at the
     stop time of sound, you may want to append some silence to sound  to  give
     the filter time to decay.

(lp sound cutoff)
     Filters sound using a first-order Butterworth low-pass filter.  Cutoff may
     be  a  float or a signal (for time-varying filtering) and expresses hertz.
     Filter coefficients (requiring  trig  functions)  are  recomputed  at  the
     sample  rate  of  cutoff.  The resulting sample rate, start time, etc. are
     taken from sound.

(tone sound cutoff)
     No  longer defined; use lp instead, or define it by adding (setfn tone lp)
     to your program.

(hp sound cutoff)
     Filters  sound  using  a first-order Butterworth high-pass filter.  Cutoff
     may be a float or a signal  (for  time-varying  filtering)  and  expresses
     hertz.    Filter coefficients (requiring trig functions) are recomputed at
     the sample rate of cutoff.  This filter is an exact complement of lp.

(atone sound cutoff)
     No longer defined; use hp instead, or define it by adding (setfn atone hp)
     to your program.

(reson sound center bandwidth n)
     Apply  a  resonating  filter  to  sound  with  center frequency center (in
     hertz), which may be a float  or  a  signal.    Bandwidth  is  the  filter
     bandwidth  (in  hertz),  which  may also be a signal.  Filter coefficients
     (requiring trig functions) are recomputed at each  new  sample  of  either
     center  or  bandwidth,  and  coefficients  are not interpolated.  The last
     parameter n specifies the type of normalization as in Csound: A value of 1
     specifies  a peak amplitude response of 1.0; all frequencies other than hz
     are attenuated.  A value of 2 specifies  the  overall  RMS  value  of  the
     amplitude response is 1.0; thus filtered white noise would retain the same
     power.  A value of zero specifies no scaling.  The resulting sample  rate,
     start time, etc. are taken from sound.

One  application  of  reson is to simulate resonances in the human vocal tract.
     See demos/voice_synthesis.htmfor sample code and documentation.

(areson sound center bandwidth n)
     The  areson  filter  is an exact complement of reson such that if both are
     applied to the same signal with  the  same  parameters,  the  sum  of  the
     results yeilds the original signal.

(shape signal table origin)
     A waveshaping function.  Use table as a function; apply  the  function  to
     each  sample  of signal to yield a new sound.  Signal should range from -1
     to +1.  Anything beyond these bounds is clipped.  Table is also  a  sound,
     but  it  is  converted  into  a  lookup  table  (similar  to  table-lookup
     oscillators).  The origin is a FLONUM and gives the time which  should  be
     considered  the  origin of table.  (This is important because table cannot
     have values at negative times, but signal will often have negative values.
     The  origin gives an offset so that you can produce suitable tables.)  The
     output at time t is:

         table(origin + clip(signal(t))

     where clip(x) = max(1, min(-1, x)).  (E.g. if table is  a  signal  defined
     over  the  interval [0, 2], then origin should be 1.0.  The value of table
     at time 1.0 will be output when the input signal is zero.)  The output has
     the same start time, sample rate, etc. as signal.  The shape function will
     also accept multichannel signals and tables.

Further discussion and examples can be  found  in  demos/distortion.htm.    The
     shape  function  is  also  used to map frequency to amplitude to achieve a
     spectral envelope for Shepard tones in demos/shepard.lsp.

(biquad signal b0 b1 b2 a0 a1 a2)
     A  fixed-parameter biquad filter. All filter coefficients are FLONUMs. See
     also  lowpass2,  highpass2,  bandpass2,  notch2,  allpass2,   eq-lowshelf,
     eq-highshelf,  eq-band,  lowpass4,  lowpass6,  highpass4, and highpass8 in
     this section for convenient variations  based  on  the  same  filter.  The
     equations for the filter are: z  = s  + a1 * z    + a2 * z   , and y  = z 
                                    n    n         n-1         n-2       n    n
     * b0 + z    * b1 + z    * b2.
             n-1         n-2
(biquad-m signal b0 b1 b2 a0 a1 a2)
     A  fixed-parameter  biquad filter with Matlab sign conventions for a0, a1,
     and a2. All filter coefficients are FLONUMs.

(lowpass2 signal hz [q])
     A  fixed-parameter,  second-order  lowpass filter based on snd-biquad. The
     cutoff frequency is given by hz (a FLONUM) and an  optional  Q  factor  is
     given by q (a FLONUM).

(highpass2 signal hz [q])
     A fixed-parameter, second-order highpass filter based on  snd-biquad.  The
     cutoff  frequency  is  given  by hz (a FLONUM) and an optional Q factor is
     given by q (a FLONUM).

(bandpass2 signal hz [q])
     A  fixed-parameter,  second-order bandpass filter based on snd-biquad. The
     center frequency is given by hz (a FLONUM) and an  optional  Q  factor  is
     given by q (a FLONUM).

(notch2 signal hz [q])
     A fixed-parameter, second-order notch  filter  based  on  snd-biquad.  The
     center  frequency  is  given  by hz (a FLONUM) and an optional Q factor is
     given by q (a FLONUM).

(allpass2 signal hz [q])
     A  fixed-parameter,  second-order  allpass filter based on snd-biquad. The
     frequency is given by hz (a FLONUM) and an optional Q factor is given by q
     (a FLONUM).

(eq-lowshelf signal hz gain [slope])
     A fixed-parameter, second-order bass  shelving  equalization  (EQ)  filter
     based  on  snd-biquad.  The hz parameter (a FLONUM)is the halfway point in
     the transition, and gain (a FLONUM) is the bass boost (or cut) in dB.  The
     optional slope (a FLONUM) is 1.0 by default, and response becomes peaky at
     values greater than 1.0.

(eq-highshelf signal hz gain [slope])
     A  fixed-parameter,  second-order treble shelving equalization (EQ) filter
     based on snd-biquad. The hz parameter (a FLONUM)is the  halfway  point  in
     the  transition,  and  gain (a FLONUM) is the treble boost (or cut) in dB.
     The optional slope (a FLONUM) is 1.0  by  default,  and  response  becomes
     peaky at values greater than 1.0.

(eq-band signal hz gain width)
     A fixed- or variable-parameter, second-order  midrange  equalization  (EQ)
     filter  based  on  snd-biquad,  snd-eqbandcv  and  snd-eqbandvvv.  The  hz
     parameter (a FLONUM) is the center frequency, gain (a FLONUM) is the boost
     (or  cut)  in  dB, and width (a FLONUM) is the half-gain width in octaves.
     Alternatively, hz, gain, and width may be SOUNDs, but they must  all  have
     the  same  sample rate, e.g. they should all run at the control rate or at
     the sample rate.

(lowpass4 signal hz)
     A  four-pole  Butterworth  lowpass  filter.  The cutoff frequency is hz (a
     FLONUM).

(lowpass6 signal hz)
     A  six-pole  Butterworth  lowpass  filter.  The  cutoff frequency is hz (a
     FLONUM).

(lowpass8 signal hz)
     An  eight-pole  Butterworth  lowpass filter. The cutoff frequency is hz (a
     FLONUM).

(highpass4 signal hz)
     A  four-pole  Butterworth  highpass  filter. The cutoff frequency is hz (a
     FLONUM).

(highpass6 signal hz)
     A  six-pole  Butterworth  highpass  filter.  The cutoff frequency is hz (a
     FLONUM).

(highpass8 signal hz)
     An  eight-pole  Butterworth highpass filter. The cutoff frequency is hz (a
     FLONUM).

(tapv sound offset vardelay maxdelay)
     A  delay line with a variable position tap.  Identical to snd-tapv. See it
     for details (5.6.2).


5.2.2.4. More Behaviors

(clip sound peak)
     Hard  limit  sound  to  the  given peak, a positive number. The samples of
     sound are constrained between an upper value of peak and a lower value  of
     N()peak. If sound is a number, clip will return sound limited by peak.  If
     sound is a multichannel sound, clip returns  a  multichannel  sound  where
     each  channel  is clipped.  The result has the type, sample rate, starting
     time, etc. of sound.

(s-abs sound)
     A  generalized  absolute  value function. If sound is a SOUND, compute the
     absolute value of each sample. If sound is  a  number,  just  compute  the
     absolute  value.  If  sound is a multichannel sound, return a multichannel
     sound with s-abs applied to each element. The result has the type,  sample
     rate, starting time, etc. of sound.

(s-sqrt sound)
     A generalized square root function. If  sound  is  a  SOUND,  compute  the
     square  root of each sample. If sound is a number, just compute the square
     root. If sound is a multichannel sound, return a multichannel  sound  with
     s-sqrt  applied  to  each  element.  The result has the type, sample rate,
     starting time, etc. of sound. In taking square roots, if an  input  sample
     is  less  than zero, the corresponding output sample is zero. This is done
     because the square root of a negative number is undefined.

(s-exp sound)
                                                                          x
     A  generalized  exponential function.  If sound is a SOUND, compute e  for
                                                           x
     each sample x.  If sound is a number x, just compute e .  If  sound  is  a
     multichannel sound, return a multichannel sound with s-exp applied to each
     element.  The result has the type, sample rate,  starting  time,  etc.  of
     sound.

(s-log sound)
     A generalized natural log function.  If sound is a  SOUND,  compute  ln(x)
     for  each sample x.  If sound is a number x, just compute ln(x).  If sound
     is a multichannel sound, return a multichannel sound with s-log applied to
     each  element.   The result has the type, sample rate, starting time, etc.
     of sound.  Note that the ln of 0 is undefined (some implementations return
     negative infinity), so use this function with care.

(s-max sound1 sound2)
     Compute the maximum of two functions, sound1  and  sound2.  This  function
     also accepts numbers and multichannel sounds and returns the corresponding
     data type. The start time of the result is the maximum of the start  times
     of  sound1 and sound2. The logical stop time and physical stop time of the
     result is the  minimum  of  the  logical  stop  and  physical  stop  times
     respectively  of sound1 and sound2. Note, therefore, that the result value
     is zero except within the bounds of both input sounds.

(s-min sound1 sound2)
     Compute  the  minimum  of  two functions, sound1 and sound2. This function
     also accepts numbers and multichannel sounds and returns the corresponding
     data  type. The start time of the result is the maximum of the start times
     of sound1 and sound2. The logical stop time and physical stop time of  the
     result  is  the  minimum  of  the  logical  stop  and  physical stop times
     respectively of sound1 and sound2. Note, therefore, that the result  value
     is zero except within the bounds of both input sounds.

(osc-note pitch [duration env loud table])
     Same as osc, but osc-note multiplies the result by env.  The env may be  a
     sound,  or  a list supplying (t  t  t  l  l  l ).  The result has a sample
                                    1  2  4  1  2  3
     rate of *sound-srate*.

(quantize sound steps)
     Quantizes  sound  as  follows: sound is multiplied by steps and rounded to
     the nearest integer. The result is then divided by steps. For example,  if
     steps is 127, then a signal that ranges from -1 to +1 will be quantized to
     255 levels (127 less than zero, 127 greater than zero, and  zero  itself).
     This  would  match the quantization Nyquist performs when writing a signal
     to an 8-bit audio file. The sound may be multi-channel.

(ramp [duration])
     Returns  a  linear  ramp  from  0  to 1 over duration (default is 1).  The
     function actually reaches 1 at  duration,  and  therefore  has  one  extra
     sample,  making  the  total duration be duration + 1/*Control-srate*.  See
     Figure  6  for  more  detail.    Ramp  is  unaffected   by   the   sustain
     transformation.    The  effect of time warping is to warp the starting and
     ending times only.  The ramp itself is unwarped (linear).  The sample rate
     is *control-srate*.

(rms sound [rate window-size])
     Computes the RMS of sound using a square window of size  window-size.  The
     result has a sample rate of rate. The default value of rate is 100 Hz, and
     the default window size is 1/rate seconds (converted to samples). The rate
     is a FLONUM and window-size is a FIXNUM.

















     Figure 6:  Ramps  generated  by  pwl  and  ramp  functions.  The  pwl
     version ramps toward the breakpoint (1, 1),  but  in  order  to  ramp
     back  to  zero  at  breakpoint  (1, 0), the function never reaches an
     amplitude  of 1.  If used at the beginning of a  seq  construct,  the
     next  sound  will begin at time 1.  The ramp version actually reaches
     breakpoint  (1, 1); notice that it is one sample longer than the  pwl
     version.    If    used in a sequence, the next sound after ramp would
     start at time 1 +  P, where P is the sample period.


(recip sound)
     A  generalized  reciprocal function.  If sound is a SOUND, compute 1/x for
     each sample x.  If sound is a number x, just compute 1/x.  If sound  is  a
     multichannel sound, return a multichannel sound with recip applied to each
     element.  The result has the type, sample rate,  starting  time,  etc.  of
     sound.    Note that the reciprocal of 0 is undefined (some implementations
     return infinity), so use this function with care on sounds.   Division  of
     sounds  is  accomplished  by  multiplying  by  the  reciprocal.  Again, be
     careful not to divide by zero.

(s-rest [duration])
     Create  silence  (zero  samples) for the given duration at the sample rate
     *sound-srate*.  Default duration is 1.0 sec, and the sound is  transformed
     in  time  according  to  *warp*.    Note:  rest is a Lisp function that is
     equivalent to cdr.  Be careful to use s-rest when you need a sound!

(noise [duration])
     Generate  noise  with  the  given  duration.  Duration (default is 1.0) is
     transformed according to *warp*.  The sample rate is *sound-srate* and the
     amplitude is +/- *loud*.

(yin sound minstep maxstep stepsize)
     Fundamental frequency estimation (pitch detection. Use the  YIN  algorithm
     to  estimate  the  fundamental  frequency of sound, which must be a SOUND.
     The minstep, a FLONUM, is the minimum  frequency  considered  (in  steps),
     maxstep,  a  FLONUM,  is  the maximum frequency considered (in steps), and
     stepsize, a FIXNUM, is the desired hop size.  The result is  a  ``stereo''
     signal,  i.e.  an array of two SOUNDs, both at the same sample rate, which
     is approximately the sample rate of sound divided by stepsize.  The  first
     SOUND consists of frequency estimates. The second sound consists of values
     that measure the confidence or reliability of the frequency estimate.    A
     small  value  (less  than  0.1) indicates fairly high confidence. A larger
     value indicates lower confidence. This number can also be thought of as  a
     ratio  of non-periodic power to periodic power. When the number is low, it
     means the signal is highly periodic at that point in time, so  the  period
     estimate  will  be  reliable.   Hint #1: See Alain de Cheveigne and Hideki
     Kawahara's article "YIN, a Fundamental Frequency Estimator for Speech  and
     Music"  in  the Journal of the Acoustic Society of America, April 2002 for
     details on the yin algorithm.  Hint #2: Typically, the stepsize should  be
     at  least  the  expected  number  of  samples  in  one  period so that the
     fundamental frequency estimates are calculated at a  rate  far  below  the
     sample  rate  of the signal. Frequency does not change rapidly and the yin
     algorithm is fairly slow. To optimize speed, you may want to use less than
     44.1  kHz sample rates for input sounds. Yin uses interpolation to achieve
     potentially fractional-sample-accurate estimates, so higher  sample  rates
     do  not  necessarily  help  the algorithm and definitely slow it down. The
                            2
     computation time is O(n ) per estimate, where n is the number  of  samples
     in  the  longest period considered. Therefore, each increase of minstep by
     12 (an octave) gives you a factor of 4 speedup, and each decrease  of  the
     sample  rate  of  sound  by  a factor of two gives you another factor of 4
     speedup. Finally, the number of estimates  is  inversely  proportional  to
     stepsize.    Hint  #3:  Use snd-srate (see Section 5.1.3) to get the exact
     sample rate of the result, which will be the sample rate of sound  divided
     by  stepsize.  E.g. (snd-srate (aref yin-output 0)), where yin-output is a
     result returned by yin, will be the sample rate of the estimates.

5.3. Transformations
  These functions change the environment  that  is  seen  by  other  high-level
functions.    Note  that  these  changes  are  usually  relative to the current
environment.  There are  also  ``absolute''  versions  of  each  transformation
function, with the exception of seq, seqrep, sim, and simrep.  The ``absolute''
versions (starting  or  ending  with  ``abs'')  do  not  look  at  the  current
environment,  but  rather  set an environment variable to a specific value.  In
this way, sections of code can be insulated from external transformations.

(abs-env beh)
     Compute  beh  in  the  default  environment.  This is useful for computing
     waveform tables and signals that are ``outside'' of time.    For  example,
     (at  10.0  (abs-env (my-beh))) is equivalent to (abs-env (my-beh)) because
     abs-env forces the default environment.

(at time beh)
     Evaluate beh with *warp* shifted by time.

(at-abs time beh)
     Evaluate beh with *warp* shifted so that local time 0 maps to time.

(continuous-control-warp beh)
     Applies  the  current  warp environment to the signal returned by beh. The
     result  has  the  default  control  sample  rate  *control-srate*.  Linear
     interpolation  is  currently  used. Implementation: beh is first evaluated
     without any shifting, stretching, or warping. The result  is  functionally
     composed with the inverse of the environment's warp function.

(continuous-sound-warp beh)
     Applies the current warp environment to the signal returned  by  beh.  The
     result   has   the   default   sound  sample  rate  *sound-srate*.  Linear
     interpolation  is  currently   used.   See   continuous-control-warp   for
     implementation notes.

(control-srate-abs srate beh)
     Evaluate beh with *control-srate*set to sample rate srate.  Note: there is
     no ``relative'' version of this function.

(extract start stop beh)
     Returns a sound which is the portion of beh between start and stop.   Note
     that  this  is done relative to the current *warp*.  The result is shifted
     to start according to *warp*, so normally the result will start without  a
     delay of start.

(extract-abs start stop beh)
     Returns a sound which is the  portion  of  beh  between  start  and  stop,
     independent  of  the  current  *warp*.    The  result  is shifted to start
     according to *warp*.

(loud volume beh)
     Evaluates beh with *loud* incremented by volume. (Recall that *loud* is in
     decibels, so increment is the proper operation.)

(loud-abs volume beh)
     Evaluates beh with *loud* set to volume.

(sound-srate-abs srate beh)
     Evaluate beh with *sound-srate* set to sample rate srate.  Note: there  is
     no ``relative'' version of this function.

(stretch factor beh)
     Evaluates beh with *warp* scaled by factor.  The effect is to  ``stretch''
     the  result of beh (under the current environment) by factor.  See Chapter
     3 for more information.

(stretch-abs factor beh)
     Evaluates  beh  with *warp* set to a linear time transformation where each
     unit of logical time maps to factor units of real time.  The effect is  to
     stretch the nominal behavior of beh (under the default global environment)
     by factor.  See Chapter 3 for more information.

(sustain factor beh)
     Evaluates   beh  with  *sustain*  scaled  by  factor.  The  effect  is  to
     ``stretch'' the result of beh (under the current environment)  by  factor;
     however,  the logical stop times are not stretched. Therefore, the overall
     duration of a sequence is not changed, and sounds will tend to overlap  if
     *sustain*  is  greater  than  one  (legato) and be separated by silence if
     *sustain* is less than one.

(sustain-abs factor beh)
     Evaluates beh with *sustain* set to factor. (See sustain, above.)

(transpose amount beh)
     Evaluates beh with *transpose* shifted by amount.  The effect is  relative
     transposition by amount semitones.

(transpose-abs amount beh)
     Evaluates beh  with  *transpose*  set  to  amount.    The  effect  is  the
     transposition  of  the  nominal  pitches  in beh (under the default global
     environment) by amount.

(warp fn beh)
     Evaluates beh with *warp* modified by fn.  The idea is that beh and fn are
     written in the same time system, and fn warps that time  system  to  local
     time.   The current environment already contains a mapping from local time
     to global (real) time.   The  value  of  *warp*  in  effect  when  beh  is
     evaluated is the functional composition of the initial *warp* with fn.

(warp-abs fn beh)
     Evaluates beh with *warp* set to fn.  In other words, the  current  *warp*
     is ignored and not composed with fn to form the new *warp*.

5.4. Combination and Time Structure
  These  behaviors  combine  component  behaviors  into  structures,  including
sequences (melodies), simultaneous sounds (chords),  and  structures  based  on
iteration.

(seq beh  [beh  ...])
        1     2
     Evaluates the first behavior beh  according to *time* and each  successive
                                     1
     behavior  at  the  logical-stop time of the previous one.  The results are
     summed to form a sound whose logical-stop is the logical-stop of the  last
     behavior  in  the  sequence.    Each behavior can result in a multichannel
     sound, in which case, the logical  stop  time  is  considered  to  be  the
     maximum  logical  stop time of any channel.  The number of channels in the
     result is the number  of  channels  of  the  first  behavior.    If  other
     behaviors  return  fewer  channels,  new  channels  are created containing
     constant zero signals until the required number of channels  is  obtained.
     If  other behaviors return a simple sound rather than multichannel sounds,
     the sound is automatically assigned to the first channel of a multichannel
     sound  that  is  then  filled  out with zero signals.  If another behavior
     returns more channels than the first behavior, the error is  reported  and
     the  computation  is  stopped.    Sample rates are converted up or down to
     match the sample rate of the first sound in a sequence.

(seqrep (var limit) beh)
     Iteratively  evaluates  beh  with  the  atom var set with values from 0 to
     limit-1, inclusive.  These sounds are placed sequentially in time as if by
     seq.  The symbol var is a read-only local variable to beh. Assignments are
     not restricted or detected, but may cause a run-time error or crash.

(sim [beh  beh  ...])
         1    2
     Returns  a  sound  which  is the sum of the given behaviors evaluated with
     current value of *warp*.  If behaviors return multiple channel sounds, the
     corresponding  channels  are  added.    If the number of channels does not
     match, the result has the maximum.  For example, if  a  two-channel  sound
     [L, R] is added to a four-channel sound [C1, C2, C3, C4], the result is [L
     + C1, R + C2, C3, C4].  Arguments to sim may also  be  numbers.    If  all
     arguments  are  numbers,  sim  is  equivalent (although slower than) the +
     function.  If a number is added to a sound, snd-offset is used to add  the
     number  to each sample of the sound.  The result of adding a number to two
     or more sounds with different durations is not  defined.    Use  const  to
     coerce  a  number  to  a  sound  of  a  specified  duration.  An important
     limitation of sim is that it cannot handle hundreds of behaviors due to  a
     stack  size  limitation  in  XLISP.    To compute hundreds of sounds (e.g.
     notes) at specified times, see timed-seq, below.  See also sum below.

(simrep (var limit) beh)
     Iteratively  evaluates  beh  with  the  atom var set with values from 0 to
     limit-1, inclusive.  These sounds are then placed simultaneously  in  time
     as if by sim.

(trigger s beh)
     Returns a sound which is the sum of instances of  the  behavior  beh.  One
     instance is created each time SOUND s makes a transition from less than or
     equal to zero to greater than zero. (If the first sample of s  is  greater
     than  zero,  an instance is created immediately.) The sample rate of s and
     all behaviors must be the same, and the  behaviors  must  be  (monophonic)
     SOUNDs.    This function is particularly designed to allow behaviors to be
     invoked in real time by making s a function of a Nyquist slider, which can
     be  controlled by a graphical interface or by OSC messages. See snd-slider
     in Section 5.6.1.

(set-logical-stop beh time)
     Returns a sound with time as the logical stop time.

(sum a [b c ...])
     Returns the sum of a, b,  c,  ...,  allowing  mixed  addition  of  sounds,
     multichannel sounds and numbers.  Identical to sim.

(mult a [b c ...])
     Returns the product of a, b, c,  ...,  allowing  mixed  multiplication  of
     sounds, multichannel sounds and numbers.

(diff a b)
     Returns the difference between a and b. This function is defined as (sum a
     (prod -1 b)).

(timed-seqscore)
     Computes sounds from a note list or ``score.'' The score is of  the  form:
     `((time1  stretch1  beh1)  (time2  stretch2 beh2) ...), where timeN is the
     starting time, stretchN is the stretch factor, and behN is  the  behavior.
     Note that score is normally a quoted list! The times must be in increasing
     order, and each behN is evaluated using lisp's eval, so the behN behaviors
     cannot refer to local parameters or local variables. The advantage of this
     form over seq is that the behaviors are evaluated one-at-a-time which  can
     take  much  less  stack space and overall memory. One special ``behavior''
     expression is interpreted  directly  by  timed-seq:  (SCORE-BEGIN-END)  is
     ignored,  not  evaluated as a function. Normally, this special behavior is
     placed at time 0 and has two parameters: the  score  start  time  and  the
     score  end time. These are used in Xmusic functions. If the behavior has a
     :pitch keyword parameter which is a list, the list represents a chord, and
     the expression is replaced by a set of behaviors, one for each note in the
     chord.  It follows that if :pitch is nil, the behavior represents  a  rest
     and is ignored.

5.5. Sound File Input and Output

(play sound)
     Play the sound through the DAC.  The play function writes a file and plays
     it.   The details of this are system-dependent, but play is defined in the
     file system.lsp.  The variable *default-sf-dir*  names  a  directory  into
     which to save a sound file.

By  default,  Nyquist  will  try  to normalize sounds using the method named by
     *autonorm-type*, which is 'lookahead by default.    The  lookahead  method
     precomputes  and  buffers  *autonorm-max-samples*  samples, finds the peak
     value,  and  normalizes  accordingly.  The  'previous  method  bases   the
     normalization  of  the  current  sound  on  the peak value of the (entire)
     previous sound. This might be good if you are  working  with  long  sounds
     that start rather softly. See Section 4.3 for more details.

If  you  want  precise control over output levels, you should turn this feature
     off by typing:

         (autonorm-off)

     Reenable the automatic normalization feature by typing:

         (autonorm-on)

Play normally produces real-time output.  The default is to send audio data  to
     the  DAC  as  it  is computed in addition to saving samples in a file.  If
     computation is slower than real-time, output will be choppy, but since the
     samples  end  up  in  a file, you can type (r) to replay the stored sound.
     Real-time playback can be disabled by:

         (sound-off)

     and reenabled by:

         (sound-on)

     Disabling real-time playback has no effect on (play-file) or (r).

(play-file filename)
     Play  the  contents of a sound file named by filename. The s-read function
     is used to read the file, and unless filename specifies an  absolute  path
     or starts with ``.'', it will be read from *default-sf-dir*.

(autonorm-on)
     Enable automatic adjustment of a scale factor applied to  sounds  computed
     using the play command.

(autonorm-off)
     Disable automatic adjustment of a scale factor applied to sounds  computed
     using the play command.

(sound-on)
     Enable real-time audio output when sound  is  computed  by  the  the  play
     command.

(sound-off)
     Disable real-time audio output when sound is  computed  by  the  the  play
     command.

(s-save  expression  maxlen filename [:format format] [:mode mode] [:bits bits]
     [:swap flag] [:play play])
     Evaluates  the  expression,  which should result in a sound or an array of
     sounds, and writes the result to the given filename.  A FLONUM is returned
     giving  the maximum absolute value of all samples written. (This is useful
     for normalizing sounds and detecting sample overflow.) If play is not NIL,
     the  sound  will  be  output  through  the computer's audio output system.
     (:play is not implemented on  all  systems;  if  it  is  implemented,  and
     filename  is  NIL,  then  this  will  play the file without also writing a
     file.)  The latency (length of audio buffering) used to play the sound  is
     0.3s by default, but see snd-set-latency.  If a multichannel sound (array)
     is written, the channels are up-sampled to the highest rate in any channel
     so  that  all  channels  have the same sample rate.  The maximum number of
     samples written per channel is given by maxlen, which allows  writing  the
     initial  part  of  a  very  long  or  infinite  sound. A header is written
     according to format, samples are encoded according  to  mode,  using  bits
     bits/sample, and bytes are swapped if swap is not NIL.  Defaults for these
     are *default-sf-format*,  *default-sf-mode*,  and  *default-sf-bits*.  The
     default  for  swap  is  NIL.  The bits parameter may be 8, 16, or 32.  The
     values for the format and mode options are described below:

  Format

snd-head-none       No header.

snd-head-AIFF       AIFF format header.

snd-head-IRCAM      IRCAM format header.

snd-head-NeXT       1024-byte NeXT/SUN format header followed by  IRCAM  header
                    ala   CMIX.      Note   that  the  NeXT/SUN  format  has  a
                    header-length field, so it really is legal to have a  large
                    header,  even  though  the normal minimal header is only 24
                    bytes.   The  additional  space  leaves  room  for  maximum
                    amplitudes,  which  can  be  used for normalizing floating-
                    point soundfiles, and for other data.  Nyquist follows  the
                    CMIX   convention   of   placing  an  IRCAM  format  header
                    immediately after the NeXT-style header.

snd-head-Wave       Microsoft Wave format header.

  Mode

snd-head-mode-adpcm ADPCM mode (not supported).

snd-head-mode-pcm   signed binary PCM mode.

snd-head-mode-ulaw  8-bit U-Law mode.

snd-head-mode-alaw  8-bit A-Law mode (not supported).

snd-head-mode-float 32-bit floating point mode.

snd-head-mode-upcm  unsigned binary PCM mode.

  The defaults for format, mode, and bits are as follows:

NeXT and Sun machines:
                    snd-head-NeXT, snd-head-mode-pcm, 16

SGI and Macintosh machines:
                    snd-head-AIFF, snd-head-mode-pcm, 16

(s-read filename [:time-offset offset] [:srate sr] [:dur dur]  [:nchans  chans]
     [:format format] [:mode mode] [:bits n] [:swap flag])
     Reads a sound from a file.  If a header is detected, the header is used to
     determine  the format of the file, and header information overrides format
     information provided by keywords (except for :time-offset and :dur).

         (s-read "mysound.snd" :srate 44100)

     specifies a sample rate of  44100  hz,  but  if  the  file  has  a  header
     specifying  22050  hz,  the  resulting  sample  rate  will  be 22050.  The
     parameters are:

        - :time-offset M the amount of time (in seconds) to skip from  the
          beginning of the file.  The default is 0.0.

        - :srate M the sample rate of the samples in the file.  Default is
          *default-sf-srate* , which is normally 44100.

        - :dur M the maximum duration in seconds  to  read.    Default  is
          10000.

        - :nchans  M  the  number of channels to read.  It is assumed that
          samples from each channel are interleaved.  Default is 1.

        - :format M the header format.  See s-save for details.    Default
          is  *default-sf-format*,  although  this  parameter is currently
          ignored.

        - :mode M the sample representation,  e.g.  PCM  or  float.    See
          s-save for details.  Default is *default-sf-format*.

        - :bits  M the number of bits per sample.  See s-save for details.
          Default is *default-sf-bits*.

        - :swap M (T or NIL) swap byte order of each  sample.  Default  is
          NIL.

     If  there  is  an  error,  for example if :time-offset is greater than the
     length of the file, then NIL is returned rather than a sound.  Information
     about the sound is also returned by s-read through *rslt*[Since XLISP does
     not support multiple value returns, multiple value returns  are  simulated
     by  having  the  function assign additional return values in a list to the
     global variable *rslt*. Since this is a global, it should be inspected  or
     copied  immediately after the function return to insure that return values
     are not overwritten by another function.]. The list assigned to *rslt*  is
     of  the  form:  (format  channels  mode  bits  samplerate  duration  flags
     byte-offset), which are defined as follows:

        - format M the header format. See s-save for details.

        - channels M the number of channels.

        - mode M the sample representation, e.g. PCM or float. See  s-save
          for details.

        - bits M the number of bits per sample.

        - samplerate M the sample rate, expressed as a FLONUM.

        - duration M the duration of the sound, in seconds.

        - flags M The values for format, channels, mode, bits, samplerate,
          and  duration  are  initially  just  the  values  passed  in  as
          parameters  or default values to s-read.  If a value is actually
          read from the sound file header, a flag is set.  The flags  are:
          snd-head-format,   snd-head-channels,  snd-head-mode,  snd-head-
          bits, snd-head-srate, and snd-head-dur.  For example,

              (let ((flags (caddr (cddddr  *rslt*))))
                (not (zerop (logand flags snd-head-srate))))

          tells whether the sample rate was specified  in  the  file.  See
          also sf-info below.

        - byte-offset  M the byte offset into the file of the first sample
          to be read  (this  is  used  by  the  s-overwrite  and  s-add-to
          functions).

(s-add-to expression maxlen filename [offset])
     Evaluates the expression, which should result in a sound or  an  array  of
     sounds,  and adds the result to the given filename.  The sample rate(s) of
     expression must match those of the file.  The maximum  number  of  samples
     written  per  channel is given by maxlen, which allows writing the initial
     part of a very long or infinite sound.  If offset is  specified,  the  new
     sound  is  added to the file beginning at an offset from the beginning (in
     seconds).  The file is  extended  if  necessary  to  accommodate  the  new
     addition,  but  if  offset falls outside of the original file, the file is
     not modified. (If necessary, use s-add-to to extend the file with zeros.)

(s-overwrite expression maxlen filename [offset])
     Evaluates  the  expression,  which should result in a sound or an array of
     sounds, and replaces samples in the given filename.  A FLONUM is returned,
     giving  the  maximum  absolute  value  of  all samples written. The sample
     rate(s) of expression must match those of the file.  The maximum number of
     samples  written  per channel is given by maxlen, which allows writing the
     initial part of a very long or infinite sound.  If  offset  is  specified,
     the  new  sound  is  written  to  the file beginning at an offset from the
     beginning (in seconds). The file is extended if necessary  to  accommodate
     the new insert, but if offset falls outside of the original file, the file
     is not modified. (If necessary, use  s-add-to  to  extend  the  file  with
     zeros.)

(sf-info filename)
     Prints information about a sound file. The parameter filename is a string.
     The  file  is  assumed to be in *default-sf-dir* (see soundfilename below)
     unless the filename begins with  ``.''  or  ``/''.  The  source  for  this
     function  is  in  the  runtime and provides an example of how to determine
     sound file parameters.

(soundfilename name)
     Converts  a string name to a soundfile name.  If name begins with ``.'' or
     ``/'', the name is returned without alteration.  Otherwise, a  path  taken
     from  *default-sf-dir*  is  prepended  to  name.   The s-plot, s-read, and
     s-save functions all use soundfilename translate filenames.

(s-plot sound n)
     Plots sound in a window.  The current implementations are minimal. For the
     RS6000/AIX implementation, s-plot simply writes time/value pairs in  ascii
     to  a  file  named  points.dat.    Then,  an xterm is created in Tektronix
     emulation mode, and the Unix plot program is used to plot the points.  The
     files used are:

     *default-plot-file* The  file  containing  the  data  points,  defaults to
                         "points.dat".

     *plotscript-file*   The file containing the script for the xterm, defaults
                         to "sys/unix/rs6k/plotscript".

The script for plotting is typically something like:

         graph < points.dat | plot -Ttek

     This  runs  the  Unix  graph program which reads the input, scales it, and
     adds axes and labels.  The output is  piped  to  the  plot  program  which
     converts  the graphics data into Tektronix commands.  It's crude but works
     well even over a serial line.

Under the  Macintosh,  plotting  is  performed  using  some  built-in  graphics
     commands. Select "Split Screen" on the Control menu to get a nice area for
     plotting.

Under Windows, using the NyqIDE program, plotting is built-in.

If you are interested in making a nicer plot program for any  platform,  please
     contact the author.

(s-print-tree sound)
     Prints  an  ascii  representation  of   the   internal   data   structures
     representing a sound.  This is useful for debugging Nyquist.  Identical to
     snd-print-tree.

5.6. Low-level Functions
  Nyquist includes many low-level functions that  are  used  to  implement  the
functions and behaviors described in previous sections. For completeness, these
functions are described here.  Remember that these are low-level functions that
are not intended for normal use.  Unless you are trying to understand the inner
workings of Nyquist, you can skip this section.



5.6.1. Creating Sounds
  The basic operations that create sounds are described here.

(snd-const value t0 srate duration)
     Returns  a  sound  with  constant  value,  starting  at  t0 with the given
     duration, at the sample rate srate.   You  might  want  to  use  pwl  (see
     Section 5.2.2.2) instead.

(snd-read filename offset t0 format channels mode bits swap sr dur)
     Loads a sound from a file with  name  filename.    Files  are  assumed  to
     consist  of a header followed by frames consisting of one sample from each
     channel.  The format specifies the type of header, but this information is
     currently  ignored.    Nyquist  looks  for  a number of header formats and
     automatically figures out which format to  read.    If  a  header  can  be
     identified,  the  header  is  first  read  from  the file.  Then, the file
     pointer is advanced by the indicated offset (in seconds).  If there is  an
     unrecognized  header,  Nyquist will assume the file has no header.  If the
     header  size  is  a  multiple  of   the   frame   size   (bytes/sample   *
     number-of-channels),  you can use offset to skip over the header.  To skip
     N bytes, use an offset of:

         (/ (float N) sr (/ bits 8) channels)

     If the header is not a multiple of the frame size, either write  a  header
     or  contact  the  author  (dannenberg@cs.cmu.edu) for assistance.  Nyquist
     will round offset to the nearest sample.  The resulting sound  will  start
     at  time t0.  If a header is found, the file will be interpreted according
     to the header information.  If no header was  found,  channels  tells  how
     many  channels  there  are, the samples are encoded according to mode, the
     sample length is bits, and sr is the sample rate.  The swap flag is  0  or
     1,  where  1  means  to  swap  sample  bytes.  The duration to be read (in
     seconds) is given by dur.  If dur is longer than the  data  in  the  file,
     then  a  shorter  duration  will  be  returned.   If the file contains one
     channel, a sound is returned.  If the file contains 2 or more channels, an
     array  of sounds is returned.  Note: you probably want to call s-read (see
     Section 5.5) instead of snd-read.  Also, see Section 5.5  for  information
     on the mode and format parameters.

(snd-save expression maxlen filename format mode bits swap play)
     Evaluates the expression, which should result in a sound or  an  array  of
     sounds,  and  writes  the result to the given filename.  If a multichannel
     sound (array) is written, the channels are up-sampled to the highest  rate
     in  any  channel  so  that  all  channels  have the same sample rate.  The
     maximum number of samples written per channel is given  by  maxlen,  which
     allows writing the initial part of a very long or infinite sound. A header
     is written according to format, samples are  encoded  according  to  mode,
     using  bits  bits/sample,  and  swapping  bytes if swap is 1 (otherwise it
     should be 0).  If play is not null, the audio is played in real  time  (to
     the  extent  possible) as it is computed.  Note: you probably want to call
     s-save (see Section 5.5) instead.  The  format  and  mode  parameters  are
     described in Section 5.5.

(snd-overwrite  expression  maxlen  filename  byte-offset  mode  bits  swap  sr
     channels)
     Evaluates  the  expression,  which should result in a sound or an array of
     sounds, and replaces samples in the given filename.  The sample rate(s) of
     expression  must match those of the file and the parameter sr. The file is
     not read to determine its format, so it is essential to specify the proper
     parameters:  byte-offset  is the offset in bytes of the first sound sample
     to be written, mode is the representation  (see  snd-save),  bits  is  the
     number  of  bits  per sample, swap is 0 or 1, where 1 means to swap sample
     bytes, sr is the sample rate, and channels is the number of  channels.  If
     these do not match the parameters for filename, it is likely that filename
     will be corrupted. Up to a maximum of maxlen samples will be  written  per
     channel.  Use  s-add-to  (in  Section  5.5  or s-overwrite (in Section 5.5
     instead of this function.

(snd-coterm s1 s2)
     Returns  a  copy  of s1, except the start time is the maximum of the start
     times of s1 and s2, and the termination time is the minimum of s1 and  s2.
     (After  the  termination time, the sound is zero as if s1 is gated by s2.)
     Some rationale follows: In order to implement s-add-to, we  need  to  read
     from  the  target sound file, add the sounds to a new sound, and overwrite
     the result back into the file.  We only want to write as many samples into
     the  file as there are samples in the new sound. However, if we are adding
     in samples read from the file, the result of a  snd-add  in  Nyquist  will
     have  the maximum duration of either sound.  Therefore, we may read to the
     end of the file.  What we need is a way  to  truncate  the  read,  but  we
     cannot  easily do that, because we do not know in advance how long the new
     sound will be. The solution is to use snd-coterm, which will allow  us  to
     truncate  the  sound  that  is  read  from  the file (s1) according to the
     duration of the new sound (s2).  When this truncated sound is added to the
     new  sound,  the  result will have only the duration of the new sound, and
     this can be used to overwrite the file.  This  function  is  used  in  the
     implementation of s-add-to, which is defined in runtime/fileio.lsp.

(snd-from-array ...)
     See page 11.

(snd-white t0 sr d)
     Generate white noise, starting at t0, with sample rate sr, and duration d.
     You probably want to use noise (see Section 5.2.2.4).

(snd-zero t0 srate)
     Creates a sound that is zero everywhere, starts at t0, and has sample rate
     srate.  The logical stop time is immediate, i.e. also at t0.  You probably
     want to use pwl (see Section 5.2.2.2) instead.

(get-slider-value index)
     Return the current value of the slider named by index  (an  integer  index
     into  the array of sliders).  Note that this ``slider'' is just a floating
     point value in an array. Sliders can  be  changed  by  OSC  messages  (see
     osc-enable)  and  by  sending  character  sequences  to Nyquist's standard
     input. (Normally,  these  character  sequences  would  not  be  typed  but
     generated  by  the jNyqIDE interactive development environment, which runs
     Nyquist as a sub-process,  and  which  present  the  user  with  graphical
     sliders.)

(snd-slider index t0 srate duration)
     Create a sound controlled by the slider named by index (an  integer  index
     into  the  array  of  sliders; see get-slider-value for more information).
     The function returns a sound. Since Nyquist sounds are computed in  blocks
     of  samples,  and  each block is computed at once, each block will contain
     copies of the current slider value. To obtain  reasonable  responsiveness,
     slider sounds should have high (audio) sample rates so that the block rate
     will be reasonably high. Also, consider lowering the audio  latency  using
     snd-set-latency. To ``trigger'' a Nyquist behavior using slider input, see
     the trigger function in Section 5.4.



5.6.2. Signal Operations
  This next set of functions take sounds as arguments,  operate  on  them,  and
return a sound.

(snd-abs sound)
     Computes a new sound where each  sample  is  the  absolute  value  of  the
     corresponding sample in sound. You should probably use s-abs instead. (See
     Section 5.2.2.4.)

(snd-sqrt sound)
     Computes  a  new  sound  where  each  sample  is  the  square  root of the
     corresponding sample in sound. If a sample is negative, it is taken to  be
     zero  to  avoid  raising  a  floating point error. You should probably use
     s-sqrt instead. (See Section 5.2.2.4.)

(snd-add sound1 sound)
     Adds  two  sounds.    The  resulting  start time is the minimum of the two
     parameter start times, the logical stop time is the  maximum  of  the  two
     parameter  stop  times,  and  the  sample  rate  is the maximum of the two
     parameter sample rates.  Use sim or sum instead of  snd-add  (see  Section
     5.4).

(snd-offset sound offset)
     Add an offset to a sound. The resulting start  time,  logical  stop  time,
     stop  time,  and  sample  rate  are  those  of sound. Use sum instead (see
     Section 5.4).

(snd-avgsound blocksize stepsize operation)
     Computes  the  averages  or  peak values of blocks of samples. Each output
     sample is an average or peak of blocksize (a fixnum) adjacent samples from
     the  input  sound.    After  each  average  or peak is taken, the input is
     advanced by  stepsize,  a  fixnum  which  may  be  greater  or  less  than
     blocksize.    The  output  sample  rate  is  the sound (input) sample rate
     divided  by  stepsize.     This   function   is   useful   for   computing
     low-sample-rate  rms  or  peak  amplitude signals for input to snd-gate or
     snd-follow.    To  select  the  operation,  operation  should  be  one  of
     OP-AVERAGE  or  OP-PEAK.    (These  are  global lisp variables; the actual
     operation parameter is an  integer.)  For  RMS  computation,  see  rms  in
     Section 5.2.2.4.

(snd-clip sound peak)
     Hard limit sound to the given peak, a  positive  number.  The  samples  of
     sound  are constrained between an upper value of peak and a lower value of
     N()peak. Use clip instead (see Section 5.2.2.4).

(snd-compose f g)
     Compose two signals, i.e.  compute f(g(t)), where f and g are sounds. This
     function is used primarily to implement time warping, but it can  be  used
     in  other applications such as frequency modulation.  For each sample x in
     g, snd-compose looks up the value of f(x) using linear interpolation.  The
     resulting  sample rate, start time, etc. are taken from g.  The sound f is
     used  in  effect  as  a  lookup  table,  but  it  is  assumed  that  g  is
     non-decreasing,  so that f is accessed in time order.  This allows samples
     of f to be computed and discarded incrementally.  If in fact g  decreases,
     the  current  sample  of g is replaced by the previous one, forcing g into
     compliance with the non-decreasing restriction.  See also sref, shape, and
     snd-resample.

For  an extended example that uses snd-compose for variable pitch shifting, see
     demos/pitch_change.htm.

(snd-tapv sound offset vardelay maxdelay)
     A  variable  delay:  sound  is  delayed  by the sum of offset (a FIXNUM or
     FLONUM) and vardelay (a SOUND).  The specified delay is adjusted to lie in
     the  range  of zero to maxdelay seconds to yield the actual delay, and the
     delay  is  implemented  using  linear  interpolation.  This  function  was
     designed  specifically  for  use  in a chorus effect: the offset is set to
     half of maxdelay, and the vardelay input is a slow sinusoid.  The  maximum
     delay is limited to maxdelay, which determines the length of a fixed-sized
     buffer.

(snd-tapf sound offset vardelay maxdelay)
     A variable delay like snd-tapv except there is no linear interpolation. By
     eliminating interpolation, the output is an exact copy of the  input  with
     no  filtering  or  distortion.  On  the other hand, delays jump by samples
     causing samples to double or skip even when the delay is changed smoothly.

(snd-copy sound)
     Makes  a  copy  of sound.  Since operators always make (logical) copies of
     their sound parameters, this  function  should  never  be  needed.    This
     function is here for debugging.

(snd-down srate sound)
     Linear interpolation of samples down to the given sample rate srate, which
     must  be  lower than the sample rate of sound.  Do not call this function.
     Nyquist performs sample-rate conversion automatically as needed.   If  you
     want to force a conversion, call force-srate (see Section 5.2.2).

(snd-exp sound)
     Compute the exponential of each sample of sound. Use  s-exp  instead  (see
     Section 5.2.2.4).

(snd-followsound floor risetime falltime lookahead)
     An envelope follower. The basic goal of this function  is  to  generate  a
     smooth  signal  that  rides  on  the  peaks of the input signal. The usual
     objective is to produce an amplitude  envelope  given  a  low-sample  rate
     (control  rate)  signal  representing  local  RMS  measurements. The first
     argument is the input signal. The floor is the minimum output  value.  The
     risetime  is  the  time  (in  seconds)  it  takes  for  the output to rise
     (exponentially) from floor to unity (1.0) and the falltime is the time  it
     takes  for  the  output  to  fall (exponentially) from unity to floor. The
     algorithm looks ahead for peaks and will  begin  to  increase  the  output
     signal  according  to  risetime  in  anticipation of a peak. The amount of
     anticipation (in sampless) is given by lookahead.   The  algorithm  is  as
     follows:  the output value is allowed to increase according to risetime or
     decrease according to falltime. If the next input sample is in this range,
     that sample is simply output as the next output sample.  If the next input
     sample is too large, the algorithm goes back in time as far  as  necessary
     to  compute  an  envelope that rises according to risetime to meet the new
     value. The algorithm will only work backward as far as lookahead.  If that
     is  not  far enough, then there is a final forward pass computing a rising
     signal from the earliest output sample. In this case,  the  output  signal
     will  be at least momentarily less than the input signal and will continue
     to rise exponentially until it intersects the input signal. If  the  input
     signal  falls faster than indicated by falltime, the output fall rate will
     be limited by falltime, and the fall in output will stop when  the  output
     reaches  floor.  This algorithm can make two passes througth the buffer on
     sharply rising inputs, so it is not particularly fast. With short  buffers
     and  low  sample  rates  this  should  not matter. See snd-avg above for a
     function that can help to generate a low-sample-rate input for snd-follow.
     See snd-chase in Section 5.6.3 for a related filter.

(snd-gate sound lookahead risetime falltime floor threshold)
     This function generates an exponential rise and decay intended  for  noise
     gate  implementation.  The  decay  starts  when  the  signal  drops  below
     threshold and stays there for longer than lookahead. Decay continues until
     the  value  reaches  floor,  at which point the decay stops and the output
     value is held constant. Either during the decay  or  after  the  floor  is
     reached,  if  the  signal goes above threshold, then the output value will
     rise to unity (1.0) at the point the signal crosses the threshold.  Again,
     look-ahead  is used, so the rise actually starts before the signal crosses
     the threshold. The rise is a constant-rate exponential and set so  that  a
     rise  from  floor  to  unity occurs in risetime.  Similarly, the fall is a
     constant-rate exponential such that a  fall  from  unity  to  floor  takes
     falltime.  The  result  is  delayed  by  lookahead,  so  the output is not
     actually synchronized with the input. To compensate, you should  drop  the
     initial lookahead of samples. Thus, snd-gate is not recommended for direct
     use. Use gate instead (see Section 5.1.4).

(snd-inverse signal start srate)
     Compute  the  function  inverse of signal, that is, compute g(t) such that
     signal(g(t)) = t.  This function assumes that signal is non-decreasing, it
     uses  linear  interpolation,  the  resulting sample rate is srate, and the
     result is shifted to have a starting time of start.  If signal  decreases,
     the  true inverse may be undefined, so we define snd-inverse operationally
     as follows: for each output time point t, scan ahead in signal  until  the
     value of signal exceeds t.  Interpolate to find an exact time point x from
     signal and output x at time t.  This function  is  intended  for  internal
     system use in implementing time warps.

(snd-log sound)
     Compute the natural logorithm of each sample of sound. Use  s-log  instead
     (see Section 5.2.2.4).

(peak expression maxlen)
     Compute the maximum absolute value of the amplitude of a sound.  The sound
     is created by evaluating expression (as in s-save).  Only the first maxlen
     samples are evaluated. The expression is automatically quoted (peak  is  a
     macro), so do not quote this parameter.  If expression is a variable, then
     the global binding of that  variable  will  be  used.    Also,  since  the
     variable retains a reference to the sound, the sound will be evaluated and
     left in memory.  See Section 4.3 on page 8 for examples.

(snd-max expression maxlen)
     Compute the maximum absolute value of the amplitude of a sound.  The sound
     is created by evaluating expression (as in snd-save), which  is  therefore
     normally  quoted by the caller.  At most maxlen samples are computed.  The
     result is the maximum of the absolute values of the samples.  Notes: It is
     recommended  to  use  peak  (see  above) instead.  If you want to find the
     maximum of a sound bound to a local variable and it is acceptable to  save
     the  samples  in  memory,  then  this  is  probably  the function to call.
     Otherwise, use peak.

(snd-maxv sound1 sound2)
     Compute  the maximum of sound1 and sound2 on a sample-by-sample basis. The
     resulting sound has its start time at the maximum of the input start times
     and a logical stop at the minimum logical stop of the inputs. The physical
     stop time is the minimum of the physical stop times  of  the  two  sounds.
     Note that this violates the ``normal'' interpretation that sounds are zero
     outside their start and stop times. For example, even  if  sound1  extends
     beyond sound2 and is greater than zero, the result value in this extension
     will be zero because it will be after the physical stop time,  whereas  if
     we  simply  treated sound2 as zero in this region and took the maximum, we
     would get a non-zero result. Use s-max instead (see Section 5.2.2.4).

(snd-normalize sound)
     Internally,  sounds  are  stored  with  a scale factor that applies to all
     samples of the sound.  All operators that take sound arguments  take  this
     scale  factor into account (although it is not always necessary to perform
     an actual multiply per sample), so you should  never  need  to  call  this
     function.    This  function multiplies each sample of a sound by its scale
     factor, returning a sound that represents the same signal, but whose scale
     factor is 1.0.

(snd-oneshotsound threshold ontime)
     Computes a new sound that is zero except where  sound  exceeds  threshold.
     From  these  points, the result is 1.0 until sound remains below threshold
     for ontime (in seconds).  The result has the same sample rate, start time,
     logical stop time, and duration as sound.

(snd-prod sound1 sound2)
     Computes the product of sound1 and sound2.  The resulting  sound  has  its
     start  time  at the maximum of the input start times and a logical stop at
     the minimum logical stop of the inputs.  Do not use this  function.    Use
     mult  or  prod instead (see Section 5.2.2).  Sample rate, start time, etc.
     are taken from sound.

(snd-pwl t0 sr lis)
     Computes a piece-wise linear function according to the breakpoints in lis.
     The starting time is t0, and the sample rate is sr.  The  breakpoints  are
     passed  in  an  XLISP list (of type LVAL) where the list alternates sample
     numbers (FIXNUMs, computed in  samples  from  the  beginning  of  the  pwl
     function)  and  values (the value of the pwl function, given as a FLONUM).
     There is an implicit starting point of (0, 0).  The list must  contain  an
     odd  number  of  points, the omitted last value being implicitly zero (0).
     The list is assumed to be well-formed.  Do not call this  function.    Use
     pwl instead (see Section 5.2.2.2).

(snd-quantize sound steps)
     Quantizes a sound. See Section 5.2.2.4 for details.

(snd-recip sound)
     Compute  the  reciprocal  of  each sample of sound. Use recip instead (see
     Section 5.2.2.4).

(snd-resample f rate)
     Resample  sound  f  using high-quality interpolation, yielding a new sound
     with the specified rate. The result is scaled by 0.95  because  often,  in
     resampling,  interpolated  values  exceed  the original sample values, and
     this could lead to clipping.  The resulting start  time,  etc.  are  taken
     from f. Use resample instead.

(snd-resamplev f rate g)
     Compose two signals, i.e.  compute f(g(t)), where f and g are sounds.  The
     result  has  sample  rate given by rate.  At each time t (according to the
     rate), g is linearly interpolated  to  yield  an  increasing  sequence  of
     high-precision  score-time values. f is then interpolated at each value to
     yield a result sample. If in fact g decreases, the current sample of g  is
     replaced  by  the  previous  one,  forcing  g  into  compliance  with  the
     non-decreasing restriction.  The result is scaled by 0.95  because  often,
     in  resampling, interpolated values exceed the original sample values, and
     this could lead to clipping. Note that if g has a high sample  rate,  this
     may  introduce  unwanted  jitter  into  sample times. See sound-warp for a
     detailed discussion. See snd-compose for a fast,  low-quality  alternative
     to  this  function.    Normally, you should use sound-warp instead of this
     function.

(snd-scale scale sound)
     Scales the amplitude of sound by the factor scale.  Use scale instead (see
     Section 5.2.2).

(snd-shape signal table origin)
     A  waveshaping function.  This is the primitive upon which shape is based.
     The snd-shape function is like shape except that signal and table must  be
     (single-channel) sounds.  Use shape instead (see Section 5.2.2.3).

(snd-up srate sound)
     Increases sample rate by linear interpolation.  The sound is the signal to
     be  up-sampled,  and  srate  is  the output sample rate.  Do not call this
     function.    Nyquist  performs  sample-rate  conversion  automatically  as
     needed.   If you want to force a conversion, call force-srate (see Section
     5.2.2).

(snd-xform sound sr time start stop scale)
     Makes  a copy of sound and then alters it in the following order:  (1) the
     start time (snd-t0) of the sound is shifted to  time,  (1)  the  sound  is
     stretched  as a result of setting the sample rate to sr (the start time is
     unchanged by this), (3) the sound is clipped from start to  stop,  (4)  if
     start  is greater than time, the sound is shifted shifted by time - start,
     so that the start time is time, (5) the sound is  scaled  by  scale.    An
     empty  (zero)  sound  at time will be returned if all samples are clipped.
     Normally, you  should  accomplish  all  this  using  transformations.    A
     transformation  applied  to  a sound has no effect, so use cue to create a
     transformable sound (see Section 5.2.1).

(snd-yin sound minstep maxstep rate)
     Identical to yin. See Section 5.2.2.4.



5.6.3. Filters
  These are also ``Signal Operators,'' the subject of the previous section, but
there are so many  filter  functions,  they  are  documented  in  this  special
section.

  Some  filters  allow  time-varying  filter  parameters.   In these functions,
filter coefficients are calculated at the sample rate of the filter  parameter,
and coefficients are not interpolated.

(snd-alpass sound delay feedback)
     An all-pass filter.  This produces a repeating  echo  effect  without  the
     resonances  of  snd-delay.   The feedback should be less than one to avoid
     exponential amplitude blowup.  Delay is rounded  to  the  nearest  sample.
     You should use alpass instead (see Section 5.2.2.3).

(snd-alpasscv sound delay feedback)
     An all-pass filter with variable feedback.  This is just  like  snd-alpass
     except  feedback  is  a sound.  You should use alpass instead (see Section
     5.2.2.3).

(snd-alpassvv sound delay feedback maxdelay)
     An  all-pass  filter  with  variable feedback and delay. This is just like
     snd-alpass  except  feedback  and  delay  are  sounds,  and  there  is  an
     additional  FLONUM  parameter,  maxdelay, that gives an upper bound on the
     value of delay. Note: delay must remain between zero and maxdelay. If not,
     results  are  undefined,  and  Nyquist  may  crash.  You should use alpass
     instead (see Section 5.2.2.3).

(snd-areson sound hz bw normalization)
     A  notch  filter  modeled  after the areson unit generator in Csound.  The
     snd-areson filter is an exact complement of snd-reson such  that  if  both
     are  applied  to  the same signal with the same parameters, the sum of the
     results  yeilds  the  original  signal.    Note  that  because   of   this
     complementary  design,  the  power is not normalized as in snd-reson.  See
     snd-reson for details on normalization.  You  should  use  areson  instead
     (see Section 5.2.2.3).

(snd-aresoncv sound hz bw normalization)
     This function  is  identical  to  snd-areson  except  the  bw  (bandwidth)
     parameter  is a sound.  Filter coefficients are updated at the sample rate
     of bw.  The ``cv'' suffix stands for Constant, Variable,  indicating  that
     hz  and  bw  are constant (a number) and variable (a sound), respectively.
     This naming convention is used throughout.  You should use areson  instead
     (see Section 5.2.2.3).

(snd-aresonvc sound hz bw normalization)
     This function is identical to snd-areson except the hz (center  frequency)
     parameter  is a sound.  Filter coefficients are updated at the sample rate
     of hz.  You should use areson instead (see Section 5.2.2.3).

(snd-aresonvv sound hz bw normalization)
     This function is identical to snd-areson except both hz (center frequency)
     and bw (bandwidth) are sounds.  Filter coefficients  are  updated  at  the
     next  sample  of  either  hz  or  bw.   You should use areson instead (see
     Section 5.2.2.3).

(snd-atone sound hz)
     A  high-pass filter modeled after the atone unit generator in Csound.  The
     snd-atone filter is an exact complement of snd-tone such that if both  are
     applied  to  the  same  signal  with  the  same parameters, the sum of the
     results yeilds the original signal.    You  should  use  hp  instead  (see
     Section 5.2.2.3).

(snd-atonev sound hz)
     This is just like snd-atone except that  the  hz  cutoff  frequency  is  a
     sound.    Filter  coefficients  are updated at the sample rate of hz.  You
     should use hp instead (see Section 5.2.2.3).

(snd-biquad sound b0 b1 b2 a1 a2 z1init z2init)
     A general second order IIR filter, where a0 is assumed to be unity. For a1
     and a2, the sign convention is opposite to that of Matlab. All  parameters
     except  the input sound are of type FLONUM. You should probably use one of
     lowpass2,  highpass2,  bandpass2,  notch2,  allpass2,   eq-lowshelf,   eq-
     highshelf, eq-band, lowpass4, lowpass6, lowpass8, highpass4, highpass6, or
     highpass8, which are all based on  snd-biquad  and  described  in  Section
     5.2.2.3.  For  completeness,  you  will  also  find  biquad  and  biquad-m
     described in that section.

(snd-chase sound risetime falltime)
     A  slew  rate limiter. The output ``chases'' the input at rates determined
     by risetime and falltime.  If the input changes too fast, the output  will
     lag behind the input. This is a form of lowpass filter, but it was created
     to turn hard-switching square waves into  smoother  control  signals  that
     could  be  used  for linear crossfades. If the input switches from 0 to 1,
     the output will linearly rise to 1  in  risetime  seconds.  If  the  input
     switches  from  1  to  0,  the  output will linearly fall to 0 in falltime
     seconds.  The generated slope is constant; the transition is linear;  this
     is  not  an  exponential  rise or fall.  The risetime and falltime must be
     scalar constants; complain to the author if  this  is  not  adequate.  The
     snd-chase  function  is  safe  for ordinary use. See snd-follow in Section
     5.6.2 for a related function.

(snd-congen gate risetime falltime)
     A  simple ``contour generator'' based on analog synthesizers.  The gate is
     a sound that normally steps from 0.0 to 1.0 at the start of an envelop and
     goes from 1.0 back to 0.0 at the beginning of the release. At each sample,
     the output converges to the input exponentially.  If gate is greater  than
     the  output,  e.g.  the  attack, then the output converges half-way to the
     output in risetime.  If the gate is less than the output, the half-time is
     falltime.     The  sample  rate,  starting  time,  logical-stop-time,  and
     terminate time are taken from gate. You should  use  congen  instead  (see
     Section 5.2.2.3.

(snd-convolve sound response)
     Convolves sound by response using a simple O(N x M) algorithm.  The  sound
     can be any length, but the response is computed and stored in a table. The
     required compuation time per sample and total space  are  proportional  to
     the length of response. Use convolve instead (see Section 5.2.2.3).

(snd-delay sound delay feedback)
     Feedback delay.  The output, initially sound, is  recursively  delayed  by
     delay,  scaled  by  feedback,  and added to itself, producing an repeating
     echo effect.  The feedback should be less than one  to  avoid  exponential
     amplitude blowup.  Delay is rounded to the nearest sample.  You should use
     feedback-delay instead (see Section 5.2.2.3)

(snd-delaycv sound delay feedback)
     Feedback delay with variable feedback.  This is just like snd-delay except
     feedback is a sound.  You should use feedback-delay instead  (see  Section
     5.2.2.3).

(snd-reson sound hz bw normalization)
     A second-order resonating (bandpass) filter with center frequency  hz  and
     bandwidth  bw,  modeled  after  the  reson  unit generator in Csound.  The
     normalization parameter must be an integer and (like in Csound)  specifies
     a  scaling  factor.    A value of 1 specifies a peak amplitude response of
     1.0; all frequencies other than hz are attenuated.  A value of 2 specifies
     the  overall  RMS  value  of  the amplitude response is 1.0; thus filtered
     white noise would retain the same power.  A value  of  zero  specifies  no
     scaling.   The result sample rate, start time, etc. are takend from sound.
     You should use reson instead (see Section 5.2.2.3).

(snd-resoncv sound hz bw normalization)
     This  function is identical to snd-reson except bw (bandwidth) is a sound.
     Filter coefficients are updated at the sample rate of bw.  You should  use
     reson instead (see Section 5.2.2.3).

(snd-resonvc sound hz bw normalization)
     This function is identical to snd-reson except hz (center frequency) is  a
     sound.    Filter  coefficients  are updated at the sample rate of hz.  You
     should use reson instead (see Section 5.2.2.3).

(snd-resonvv sound hz bw normalization)
     This function is identical to snd-reson except botth hz (center frequency)
     and bw (bandwidth) are sounds.  Filter coefficients  are  updated  at  the
     next  sample  from  either  hz  or  bw.  You should use reson instead (see
     Section 5.2.2.3).

(snd-tone sound hz)
     A  first-order recursive low-pass filter, based on the tone unit generator
     of Csound.  The hz parameter is the cutoff frequency, the response curve's
     half-power  point.    The  result sample rate, start time, etc. are takend
     from sound.  You should use lp instead (see Section 5.2.2.3).

(snd-tonev sound hz)
     This  function  is identical to snd-tone except hz (cutoff frequency) is a
     sound.  The filter coefficients are updated at the sample rate of hz.  You
     should use lp instead (see Section 5.2.2.3).



5.6.4. Table-Lookup Oscillator Functions
  These  functions  all  use  a  sound  to  describe  one  period of a periodic
waveform.  In the current implementation, the sound samples are  copied  to  an
array (the waveform table) when the function is called.  To make a table-lookup
oscillator generate a specific  pitch,  we  need  to  have  several  pieces  of
information:

   - A  waveform  to  put  into  the  table.    This  comes from the sound
     parameter.

   - The length (in samples) of the waveform.  This is obtained by reading
     samples  (starting at the sound's start time, not necessarily at time
     zero) until the physical stop time of the sound.  (If  you  read  the
     waveform from a file or generate it with functions like sim and sine,
     then the physical and logical stop times will be the  same  and  will
     correspond  to  the  duration  you  specified, rounded to the nearest
     sample.)

   - The intrinsic sample rate of the  waveform.    This  sample  rate  is
     simply the sample rate property of sound.

   - The  pitch  of  the waveform.  This is supplied by the step parameter
     and indicates the pitch (in steps) of sound.  You might  expect  that
     the pitch would be related to the period (length) of sound, but there
     is the interesting case that synthesis based on sampling often  loops
     over  multiple periods.  This means that the fundamental frequency of
     a generated tone may be some  multiple  of  the  looping  rate.    In
     Nyquist,  you  always specify the perceived pitch of the looped sound
     if the sound is played at the sound's own sample rate.

   - The desired pitch.  This is specified by the hz  parameter  in  Hertz
     (cycles  per second) in these low-level functions.  Note that this is
     not necessarily the ``loop'' rate at  which  the  table  is  scanned.
     Instead,  Nyquist  figures  what  sample  rate  conversion  would  be
     necessary to ``transpose'' from the step which specifies the original
     pitch  of  sound to hz, which gives the desired pitch.  The mixed use
     of steps and Hertz came about because it seemed  that  sample  tables
     would  be  tagged  with  steps  (``I  sampled  a middle-C''), whereas
     frequency deviation in the fmosc function is linear, thus calling for
     a specification in Hertz.

   - The desired sample rate.  This is given by the sr parameter in Hertz.

  Other parameters common to all of these oscillator functions are:

   - t0, the starting time, and

   - phase,  the  starting  phase  in  degrees.    Note  that  if the step
     parameter indicates that the table holds more  than  one  fundamental
     period,  then  a  starting  phase  of  360  will  be different than a
     starting phase of 0.

(snd-amosc sound step sr hz t0 am phase)
     An  oscillator  with  amplitude  modulation.    The sound am specifies the
     amplitude and the logical stop time.  The physical stop time is also  that
     of am.  You should use amosc instead (see Section 5.2.2.1).

(snd-fmosc s step sr hz t0 fm phase)
     A Frequency Modulation oscillator.    The  sound  fm  specifies  frequency
     deviation  (in  Hertz) from hz.  You should use fmosc instead (see Section
     5.2.2.1).

(snd-buzz n sr hz t0 fm)
     A buzz oscillator, which generates n harmonics of equal amplitude.  The fm
     specifies frequency deviation (in Hertz) from hz.   You  should  use  buzz
     instead (see Section 5.2.2.1).

(snd-pluck sr hz t0 d final-amp)
     A  Karplus-Strong  plucked  string  oscillator  with   sample   rate   sr,
     fundamental  frequency hz, starting time t0, duration d, initial amplitude
     approximately 1.0 (not exact because the string is initialized with random
     values)  and final amplitude approximately final-amp. You should use pluck
     instead (see Section 5.2.2.1).

(snd-osc s step sr hz t0 d phase)
     A  simple table lookup oscillator with fixed frequency.  The duration is d
     seconds.  You should use osc instead (see Section 5.2.2.1).

(snd-partial sr hz t0 env)
     This  is a special case of snd-amosc that generates a sinusoid starting at
     phase 0 degrees.  The env  parameter  gives  the  envelope  or  any  other
     amplitude  modulation.    You  should  use  partial  instead  (see Section
     5.2.2.1).

(snd-sine t0 hz sr d)
     This  is  a  special case of snd-osc that always generates a sinusoid with
     initial phase of 0 degrees.  You should  use  sine  instead  (see  Section
     5.2.2.1).

(snd-siosc tables sr hz t0 fm)
     A Spectral Interpolation Oscillator with frequency modulation. The  tables
     is  a  list  of sounds and sample counts as follows: (table0 count1 table1
     ... countN tableN). The initial waveform is  given  by  table0,  which  is
     interpolated linearly to table1 over the first count1 samples. From count1
     to count2 samples, the waveform is interpolated from table1 to table2, and
     so  on.  If more than countN samples are generated, tableN is used for the
     remainder of the sound. The duration and logical stop time of the sound is
     taken  from fm, which specified frequency modulation (deviation) in Hertz.
     You should use siosc instead (see Section 5.2.2.1).



5.6.5. Physical Model Functions
  These functions perform some sort of physically-based modeling synthesis.

(snd-clarinet freq breath-env sr)
     A  clarinet  model  implemented  in  STK.  The  freq is a FLONUM in Hertz,
     breath-env is a SOUND that ranges from zero to one, and sr is the  desired
     sample  rate  (a  FLONUM).  You  should  use clarinet instead (see Section
     5.2.2).

(snd-clarinet-freq freq breath-env freq-env sr)
     A  clarinet  model just like snd-clarinet but with an additional parameter
     for continuous frequency control. You  should  use  clarinet-freq  instead
     (see Section 5.2.2).

(snd-clarinet-all    freq   vibrato-freq   vibrato-gain   freq-env   breath-env
     reed-stiffness noise sr)
     A   clarinet   model  just  like  snd-clarinet-freq  but  with  additional
     parameters for vibrato generation and continuous control of reed stiffness
     and breath noise. You should use clarinet-all instead (see Section 5.2.2).

(snd-sax freq breath-env sr)
     A sax model implemented in STK. The freq is a FLONUM in Hertz,  breath-env
     is a SOUND that ranges from zero to one, and sr is the desired sample rate
     (a FLONUM). You should use sax instead (see Section 5.2.2).

(snd-sax-freq freq freq-env breath-env sr)
     A  sax  model  just  like  snd-sax  but  with  an additional parameter for
     continuous frequency control. You should use sax-freq instead (see Section
     5.2.2).

(snd-sax-all  freq vibrato-freq vibrato-gain freq-env breath-env reed-stiffness
     noise blow-pos reed-table-offset sr)
     A  sax  model  just  like  snd-sax-freq but with additional parameters for
     vibrato generation and continuous control of reed stiffness, breath noise,
     excitation  position,  and  reed  table  offset.    You should use sax-all
     instead (see Section 5.2.2).



5.6.6. Sequence Support Functions
  The next two functions are used to implement Nyquist's seq construct.

(snd-seq sound closure)
     This  function  returns sound until the logical stop time of sound.  Then,
     the XLISP closure is evaluated, passing it the logical stop time of  sound
     as  a  parameter.  The closure must return a sound, which is then added to
     sound.  (An add is used so that sound can continue past its  logical  stop
     if desired.)  Do not call this function.  See seq in Section 5.4.

(snd-multiseq array closure)
     This function is similar to  snd-seq  except  the  first  parameter  is  a
     multichannel  sound  rather  than a single sound.  A multichannel sound is
     simply an XLISP array of sounds.  An array of sounds is returned which  is
     the  sum  of  array  and another array of sounds returned by closure.  The
     closure is passed the logical stop time of the multichannel  sound,  which
     is  the  maximum  logical  stop time of any element of array.  Do not call
     this function.  See seq in Section 5.4.

  (snd-trigger s closure)
This  is  one  of  the only ways in which a behavior instance can be created by
changes in a signal. When s (a SOUND) makes a  transition  from  less  than  or
equal  to  zero  to greater than zero, the closure, which takes a starting time
parameter, is evaluated. The closure must return a SOUND. The sum of all  these
sounds  is  returned. If there are no sounds, the result will be zero. The stop
time of the result is the maximum stop time of s and all sounds returned by the
closure.  The  sample rate of the return value is the sample rate of s, and the
sounds returned by the closure must all have that same sample rate. Do not call
this function.  See trigger in Section 5.4.

  An  implementation  note:  There  is  no  way  to  have  snd-trigger return a
multichannel sound. An alternative implementation would be a built-in  function
to  scan  ahead  in  a  sound to find the time of the next zero crossing.  This
could be combined with some LISP code similar to seq to sum up instances of the
closure. However, this would force arbitrary look-ahead and therefore would not
work with real-time inputs, which was the motivation  for  snd-trigger  in  the
first place.
6. Nyquist Globals
  There  are many global variables in Nyquist. A convention in Lisp is to place
asterisks (*) around global variables, e.g. *table*. This is only a convention,
and  the  asterisks are just like any other letter as far as variable names are
concerned. Here are some globals users should know about:

*table*             Default table used by osc and other oscillators.

*A4-Hertz*          Frequency  of  A4  in   Hertz..   Note:   you   must   call
                    (set-pitch-names)   to  recompute  pitches  after  changing
                    *A4-Hertz*.

*autonorm*          The normalization factor to be applied to  the  next  sound
                    when  *autonorm-type*  is  'previous.  See Sections 4.3 and
                    5.5.

*autonormflag*      Enables the automatic normalization  feature  of  the  play
                    command.  You  should  use (autonorm-on) and (autonorm-off)
                    rather than setting *autonormflag* directly.  See  Sections
                    4.3 and 5.5.

*autonorm-max-samples*
                    Specifies how many samples will be computed searching for a
                    peak value when *autonorm-type* is 'lookahead. See Sections
                    4.3 and 5.5.

*autonorm-previous-peak*
                    The  peak  of the previous sound generated by play. This is
                    used to compute the scale factor for the  next  sound  when
                    *autonorm-type* is 'previous. See Sections 4.3 and 5.5.

*autonorm-target*   The  target  peak  amplitude  for the autonorm feature. The
                    default value is 0.9. See Sections 4.3 and 5.5.

*autonorm-type*     Determines how the autonorm feature is  implemented.  Valid
                    values  are  'lookahead  (the  default)  and 'previous. See
                    Sections 4.3 and 5.5.

*breakenable*       Controls whether XLISP enters a break loop when an error is
                    encountered. See Section IV.14.

*control-srate*     Part  of  the  environment,  establishes the control sample
                    rate. See Section 2.1 for details.

*default-sf-bits**default-sf-bits
                    The default bits-per-sample for sound files. Typically 16.

*default-sf-dir*    The  default  sound file directory.  Unless you give a full
                    path for a file, audio files are  assumed  to  be  in  this
                    directory.

*default-sf-format* The  default sound file format. When you write a file, this
                    will be the default format: AIFF  for  Mac  and  most  Unix
                    systems, NeXT for NeXT systems, and WAV for Win32.

*default-sf-srate*  The default sample rate for sound files. Typically 44100.0,
                    but often set to 22050.0 for speed in non-critical tasks.

*default-control-srate*
                    Default  value  for *control-srate*. This value is restored
                    when you execute (top) to pop out of a  debugging  session.
                    Change it by calling (set-control-srate value).

*default-sound-srate*
                    Default value for *sound-srate*.  This  value  is  restored
                    when  you  execute (top) to pop out of a debugging session.
                    Change it by calling (set-sound-srate value).

*file-separator*    The character that separates directories in  a  path,  e.g.
                    ``/''  for  Unix, ``:'' for Mac, and ``\'' for Win32.  This
                    is normally set in system.lsp.

*rslt*              When a function returns more than one value, *rslt* is  set
                    to  a  list  of  the  ``extra''  values.  This  provides  a
                    make-shift version of the multiple-value-return facility in
                    Common Lisp.

*sound-srate*       Part of the environment, establishes the audio sample rate.
                    See Section 2.1 for details.

*soundenable*       Controls whether writes to a sound file will also be played
                    as  audio.    Set  this  variable  by calling (sound-on) or
                    (sound-off).

*tracenable*        Controls whether XLISP prints a backtrace when an error  is
                    encountered.

XLISP variables     See Section IV.14 for a list of global variables defined by
                    XLISP.

Environment variables
                    See  Section  2.1  for definitions of variables used in the
                    environment for behaviors. In general, you should never set
                    or access these variables directly.

Various constants   See Section 1.4 for definitions of predefined constants for
                    loudness, duration, and pitch.
7. Time/Frequency Transformation
  Nyquist provides functions for FFT and inverse FFT operations on  streams  of
audio  data.    Because  sounds  can be of any length, but an FFT operates on a
fixed amount of data, FFT processing is  typically  done  in  short  blocks  or
windows  that move through the audio. Thus, a stream of samples is converted in
to a sequence of FFT frames representing short-term spectra.

  Nyquist does not have a special data type corresponding to a sequence of  FFT
frames.    This  would  be  nice,  but it would require creating a large set of
operations suitable for  processing  frame  sequences.  Another  approach,  and
perhaps  the  most  ``pure''  would  be  to  convert  a  single  sound  into  a
multichannel sound, with one channel per bin of the FFT.

  Instead, Nyquist violates  its  ``pure''  functional  model  and  resorts  to
objects  for  FFT  processing.  A sequence of frames is represented by an XLISP
object. Whenever you send the selector :next to the object, you get back either
NIL,  indicating  the  end  of  the  sequence,  or  you  get  an  array  of FFT
coefficients.

  The Nyquist function snd-fft (mnemonic, isn't it?) returns one of  the  frame
sequence  generating objects. You can pass any frame sequence generating object
to another function, snd-ifft, and turn the sequence back into audio.

  With snd-fft and snd-ifft, you can create all sorts of interesting processes.
The  main  idea is to create intermediate objects that both accept and generate
sequences of frames.  These objects can operate on the frames to implement  the
desired  spectral-domain  processes.  Examples of this can be found in the file
fft_tutorial.htm,  which  is  part  of  the  standard  Nyquist   release.   The
documentation for snd-fft and snd-ifft follows.

(snd-fft sound length skip window)
     This function performs an FFT on the first samples in sound and returns  a
     Lisp  array  of  FLONUMs.   The function modifies the sound, violating the
     normal rule that sounds are immutable in Nyquist, so it  is  advised  that
     you  copy  the  sound  using snd-copy if there are any other references to
     sound. The length of the FFT is specified by length, a  FIXNUM  (integer).
     After  each  FFT,  the  sound  is  advanced  by skip samples, also of type
     FIXNUM. Overlapping FFTs, where skip is less than length, are allowed.  If
     window is not NIL, it must be a sound.  The first length samples of window
     are multiplied by length samples of sound before performing the FFT.  When
     there  are  no  more  samples in sound to transform, this function returns
     NIL. The coefficients  in  the  returned  array,  in  order,  are  the  DC
     coefficient,  the  first  real,  the first imaginary, the second real, the
     second imaginary, etc. If the length  is  even,  the  last  array  element
     corresponds to the real coefficient at the Nyquist frequency.

(snd-ifft time srate iterator skip window)
     This function performs an IFFT on a sequence of spectral  frames  obtained
     from iterator and returns a sound. The start time of the sound is given by
     time. Typically, this would be computed by  calling  (local-to-global  0).
     The sample rate is given by srate. Typically, this would be *sound-srate*,
     but it might also depend upon the sample rate of the sound from which  the
     spectral frames were derived. To obtain each frame, the function sends the
     message :next to the iterator object, using XLISP's primitives for objects
     and  message passing. The object should return an array in the same format
     as obtained from snd-fft, and the object should return NIL when the end of
     the  sound  is  reached.  After each frame is inverse transformed into the
     time domain, it is added to the resulting sound. Each successive frame  is
     added  with  a  sample  offset  specified by skip relative to the previous
     frame. This must be an integer greater than zero. If window is not NIL, it
     must  be  a  sound.  This  window  signal  is  multiplied  by  the inverse
     transformed frame before the frame is  added  to  the  output  sound.  The
     length  of  each  frame  should  be the same. The length is implied by the
     array returned by iterator, so it does not appear  as  a  parameter.  This
     length  is  also the number of samples used from window. Extra samples are
     ignored, and window is padded with zeros if necessary, so be  sure  window
     is  the  right  length.  The resulting sound is computed on demand as with
     other Nyquist sounds, so :next messages are sent to iterator only when new
     frames  are  needed. One should be careful not to reuse or modify iterator
     once it is passed to snd-ifft.
8. MIDI, Adagio, and Sequences
  Nyquist includes facilities to read and write MIDI files as well as an  ASCII
text-based score representation language, Adagio. XLISP and Nyquist can be used
to generate MIDI files using compositional algorithms. (See also  Section  11.)
A  tutorial  on  using  the  Adadio  representation  and  MIDI  can be found in
demos/midi_tutorial.htm. The Adagio language is  described  below.  Adagio  was
originally  developed as part of the CMU MIDI Toolkit, which included a program
to record and play MIDI using the  Adagio  representation.  Some  of  the  MIDI
features of Adagio may not be useful within Nyquist.

  Nyquist  offers a number of different score representations, and you may find
this confusing. In general, MIDI files are  a  common  way  to  exchange  music
performance  data,  especially  with sequencers and score notation systems. The
demos/midi_tutorial.htm examples show how to get the most precise control  when
generating  MIDI  data.  Adagio  is  most  useful  as  a text-based score entry
language, and it is certainly more compact than Lisp expressions for  MIDI-like
data.  The  Xmusic  library  (Chapter 11) is best for algorithmic generation of
music and score manipulation.  There  are  functions  to  convert  between  the
Adagio, MIDI sequence data, and Xmusic score representations.

  Adagio    is  an easy-to-use, non-procedural notation for scores.  In Adagio,
text commands are used to specify each note.  If you are new to Adagio, you may
want  to  glance  at  the  examples  in  Section 8.3 starting on page 28 before
reading any further.

  A note is described in Adagio by a set of attributes, and any  attribute  not
specified  is  ``inherited''  from the previous line.  Attributes may appear in
any order and must be separated by one or more blanks.  An  attribute  may  not
contain  any blanks.  The attributes are:  time, pitch, loudness, voice number,
duration, and articulation.

  Adagio  has  been  used  to  program  a  variety  of  hardware  and  software
synthesizers,   and   the   Adagio  compiler  can  be  easily  adapted  to  new
environments.  Although not originally intended for MIDI,  Adagio  works  quite
well  as  a  representation for MIDI scores.  Adagio has been extended to allow
MIDI controller data such as modulation wheels, pitch bend,  and  volume,  MIDI
program commands to change timbre, and System Exclusive messages.

  A  note command in Adagio must be separated from other notes.  Usually, notes
are distinguished by writing each one on a separate line.  Notes  can  also  be
separated by using a comma or semicolon as will be described below.

  Besides notes, there are several other types of commands:

   1. An  asterisk  (*)  in  column  one  (or  immediately  after a comma,
      semicolon, or space) indicates that  the  rest  of  the  line  is  a
      comment.  The line is ignored by Adagio, and is therefore a good way
      to insert text to be read by people.  Here are some examples:

          * This is a comment.
          T150 G4  * This is a comment too!
          T150 G4  ;* So is this.

   2. An empty command (a blank line, for example) is  ignored  as  if  it
      were  a comment(To be consistent, a blank line ought to specify zero
      attributes and generate a note that inherits all of  its  attributes
      from the previous one.  Adagio is intentionally inconsistent in this
      respect.).

   3. An exclamation point (!) in column one (or immediately after a comma
      or  semicolon)  indicates a special command.  A special command does
      not generate a note.  Special commands  follow  the  ``!''  with  no
      intervening spaces and extend to the end of the line, for example:

          !TEMPO 100

   4. Control  change  commands  are used to control parameters like pitch
      bend, modulation, and program (timbre).  Control change commands can
      be  specified  along  with  notes  or by themselves.  A command that
      specifies control  changes  without  specifying  a  pitch  will  not
      produce a note.

  Adagio is insensitive to case, thus ``A'' is equivalent to ``a'', and you can
mix upper and lower case letters freely.

8.1. Specifying Attributes
  A note is indicated by a set of attributes.  Attributes are  indicated  by  a
string  of  characters  with  no  intervening  spaces  because  spaces separate
attributes.  The attributes are described below.
                                                th
  The default unit of time is a centisecond (100  's), but this can be  changed
                        th
to  a  millisecond (1000  's) using the !MSEC command and reset to centiseconds
with !CSEC (see Section 8.4.1).  In the descriptions  below,  the  term  ``time
unit'' will be used to mean whichever convention is currently in effect.



8.1.1. Time
  The  time attribute specifies when to start the note.  A time is specified by
a ``T'' followed  by  a  number  representing  time  units  or  by  a  duration
(durations are described below).  Examples:

    T150    ** 1.5 sec (or .15 sec)
    TQ3     ** 3 quarter note's duration

If  no  time is specified, the default time is the sum of the time and duration
attributes of the previous note.  (But see Section  8.1.4.)  Time  is  measured
relative  to  the  time  of  the  most  recent Tempo or Rate command.  (See the
examples in Section 8.3 for some clarification of this point.)



8.1.2. Pitch
  The pitch attribute specifies what frequency  to  produce.    Standard  scale
pitches  are  named  by name, using S for sharp, F for flat, and (optionally) N
for natural.  For example, C and CN represent the same pitch, as do FS  and  GF
(F sharp and G flat).  Note that there are no bar lines, and accidentals to not
carry forward to any other notes as in common practice notation.

  Octaves are specified by number. C4 is middle C, and B3 is a half step lower.
F5  is  the top line of the treble clef, etc.  (Adagio octave numbering follows
the ISO standard, but note that this is not universal.  In  particular,  Yamaha
refers  to  middle  C  as  C3.)   Accidentals can go before or after the octave
number, so FS3 and F3S have the same meaning.

  An alternate notation for pitch is Pn, where n is an integer representing the
pitch.Middle C (C4) is equivalent to P60, CS4 is P61, etc.

  If  you  do  not  specify an octave, Adagio will choose one for you.  This is
done by picking the octave that will make the current pitch  as  close  to  the
previous  pitch  as  possible.   In the case of augmented fourths or diminished
fifths, there are two equally good choices.  Adagio chooses the lower octave.



8.1.3. Duration
  Duration is specified by a letter indicating a number of beats,  followed  by
one or several modifiers.  The basic duration codes are:

    W (whole, 4 beats),
    H (half, 2 beats),
    Q (quarter, 1 beat),
    I (eighth, 1/2 beat),
    S (sixteenth, 1/4 beat),
    % (thirtysecond, 1/8 beat), and
    ^ (sixtyfourth, 1/16 beat).

Note  that  E is a pitch, so eighth-notes use the duration code I.  The default
tempo is 100 beats per minute  (see  Section  8.1.10).    These  codes  may  be
followed  by a T (triplet), indicating a duration of 2/3 the normal.  A dot (.)
after a duration code extends it by half to 3/2 the normal.  An integer after a
note  multiplies  its duration by the indicated value (the result is still just
one note).  Finally, a slash followed by an integer divides the duration by the
integer.    Like  all  attributes,  duration  attributes  may not have embedded
spaces.  Examples:

    Q    1   beat (quarter note)
    QT   2/3 beat (quarter triplet)
    W.   6   beats(dotted whole note)
    ST6  1   beat (6 sixteenth triplets)
    H5   10  beats(5 half notes)
    Q3/7 3/7 beats

                                                                    th
A duration may be noted by Un, where n is an integer indicating  100  's  of  a
                th
second  (or 1000  's), see Section 8.4.1.  For example, U25 is twenty-five time
units.

  Durations may be combined using a plus sign:

    Q+IT        ** a quarter tied to an eighth triplet
    Q/7+W+Q2/7  ** a 7th beat tied to a whole tied to 2/7th beat
    Q+U10       ** a quarter plus 10 time units



8.1.4. Next Time
  The time of the next command (the next command in the Adagio program text) is
normally  the time of the current note command plus the duration of the current
note.  This can be overridden by a field consisting of the letter N followed by
a  number  indicating time units, or followed by a duration as described above.
The next note will then start at the time of the current note plus the duration
specified  after  N.  If the next note has an explicit time attribute (T), then
the specified time will override the one based on the previous note.  Examples:

    N0      ** start the next note at the same time as this one
    N50     ** start the next note 0.5 seconds after this one
    NQT     ** start the next note 2/3 beat after the current one
    NU10+Q  ** start after 0.1 seconds plus a quarter

A comma has an effect  similar  to  N0  and  is  explained  in  Section  8.4.2.
Articulation  effects  such as staccato can be produced using N, but it is more
convenient to use the articulation attribute described in Section 8.1.6.



8.1.5. Rest
  Rests are obtained by including the field R in a note command.  The effect of
an  R field is to omit the note that would otherwise occur as the result of the
current note command.  In all other respects, the  command  is  processed  just
like  any  other  line.  This means that attributes such as duration, loudness,
and pitch can be specified, and anything specified will  be  inherited  by  the
note in the next command.  Normally, a rest will include just R and a duration.
The fact that a note command specifies a rest is not inherited.  For example:

    R H     ** a half (two beat) rest
    RH      ** illegal, R must be separated from H by space(s)
Because some  synthesizers  (e.g.  a  DX7)  cannot  change  programs  (presets)
rapidly,  it  may  be  desirable  to  change  programs  in  a  rest so that the
synthesizer will be ready to play by the end of the rest.   See  Section  8.1.9
for an example.



8.1.6. Articulation
  Articulation in Adagio refers to the percentage of time a note is on relative
to the indicated duration.  For example, to play a  note  staccato,  you  would
normally  play  the  note  about  half  of  its indicated duration.  In Adagio,
articulation is indicated by # followed  by  an  integer  number  indicating  a
percentage.    The  articulation attribute does not affect the time of the next
command.  This example plays two staccato quarter notes:

    C Q #50
    D

To produce overlapping notes, the articulation may be greater than 100.
Be aware that overlapping notes on the same pitch can be  a  problem  for  some
synthesizers.  The following example illustrates this potential problem:

    !TEMPO 60
    C Q #160   * starts at time 0,   ends at 1.6 sec
    D I        * starts at time 1,   ends at 1.8 sec
    C Q        * starts at time 1.5, ends at 3.1 sec?

At  one beat per second (tempo 60), these three notes will start at times 0, 1,
and 1.5 seconds, respectively.  Since these notes have an articulation of  160,
each will be on 160% of its nominal duration, so the first note (C) will remain
on until 1.6 seconds.  But the third note (another C) will start  at  time  1.5
seconds.    Thus,  the  second  C  will  be  started before the first one ends.
Depending on the synthesizer, this may cancel the first C or play a second C in
unison.    In either case, a note-off message will be sent at time 1.6 seconds.
If this cancels the second C, its actual duration will be 0.1 rather  than  1.6
seconds as intended.  A final note-off will be sent at time 3.1 seconds.



8.1.7. Loudness
  Loudness  is  indicated  by  an  L  followed  by  a  dynamic marking from the
following: PPP, PP, P, MP, MF, F, FF, FFF.  Alternatively, a number from  1  to
127 may be used.  The loudness attribute is the MIDI note velocity.  (Note that
a MIDI velocity of 0 means ``note-off,'' so the minimum loudness is  1.)    The
dynamicmarkings are translated into numbers as follows:

    Lppp    20                    Lmf     58
    Lpp     26                    Lf      75
    Lp      34                    Lff     98
    Lmp     44                    Lfff    127



8.1.8. Voice
  The  voice attribute tells which of the 16 MIDI channels to use for the note.
The voice attribute consists of a V followed by an integer from 1 (the default)
to 16.
There  is  a  limit to how many notes can be played at the same time on a given
voice (MIDI channel).  Since the limit depends  upon  the  synthesizer,  Adagio
cannot  tell  you  when  you  exceed  the limit.  Similarly, Adagio cannot tell
whether your synthesizer is set up to respond to a given channel, so  there  is
no guarantee that what you write will actually be heard.



8.1.9. Timbre (MIDI Program)
  A  MIDI  program (synthesizer preset) can be selected using the attribute Zn,
where n is the program number (from 1 to 128).  Notice that in  MIDI,  changing
the  program  on  a  given  channel  will  affect all notes on that channel and
possibly others.  Adagio treats MIDI program  changes  as  a  form  of  control
change.
For  many synthesizers, you will not be able to change programs at the start of
a note or during a note.  Change the  program  during  a  rest  instead.    For
example:

    R I Z23 V4      ** change MIDI channel 4 to program 23 during rest
    A4              ** play a note on channel 4

Check  how  your  synthesizer  interprets  program  numbers.   For example, the
cartridge programs on a DX7 can be accessed  by  adding  32  to  the  cartridge
program number.  Cartridge program number 10 is specified by Z42.
  As  in  MIDI, the Adagio timbre is a property of the voice (MIDI channel), so
the timbre will not be inherited by notes on a different channel; to change the
timbre on multiple voices (channels), you must explicitly notate each change.



8.1.10. Tempo
  The length of a beat may be changed using a Tempo command:

    !TEMPO n

where  n  indicates  beats  per minute.  The exclamation mark tells Adagio that
this is a special command line rather  than  a  note  definition.    A  special
command takes the place of a note specification.  No other attributes should be
written on a line with a special command.  The  !TEMPO  command  is  associated
with a time, computed as if the !TEMPO command were a note.  The time attribute
(T) of all succeeding notes is now measured relative to the time of the  !TEMPO
command.    The  new  tempo  starts  at the !TEMPO command time and affects all
succeeding notes.  Durations specified in time units (for example U58, N15) are
not  affected by the !TEMPO command, and numerical times (for example T851) are
computed relative to the time of the last !TEMPO command.

  The !TEMPO command is fairly clever about default durations.    If  the  last
duration  specified before the !TEMPO command is symbolic (using one of ^,%, S,
I, Q, H, or W ), then the default  duration  for  the  node  after  the  !TEMPO
command will be modified according to the tempo change.  Consider the following
tempo change:

    !TEMPO 60
    A4 H
    !TEMPO 120
    G

In this example, the first note will last 2 seconds (2 beats at  60  beats  per
minute).  The second note inherits the duration (H) from the first note, but at
120 beats per minute, the second note will last only 1 second.  If the duration
had  been  specified U200 (also a duration of 2 seconds), the second note would
also last 2 seconds because  the  !TEMPO  command  does  not  affect  times  or
durations specified numerically in time units.  If the duration is the sum of a
symbolic and a numeric specification, the inherited  duration  after  a  !TEMPO
command is undefined.



8.1.11. Rate
  The !RATE command scales all times including those specified in hundredths of
seconds.  A rate of 100 means no change, 200 means twice as fast, and 50  means
half  as  fast.   For example, to make a piece play 10% faster, you can add the
following command at the beginning of the score:

    !RATE 110

!RATE and !TEMPO commands combine, so

    !RATE 200
    !TEMPO 70

will play 70 beats per minute at double the normal  speed,  or  140  beats  per
minute.    Like  !TEMPO,  the  time  of  the !RATE command is added to the time
attribute of all following notes up to the next !TEMPO or !RATE command.

  Two !RATE commands do not combine, so a !RATE command only affects  the  rate
until the next !RATE command.

  Although  !TEMPO  and  !RATE  can  occur in the middle of a note (using N, T,
etc.) they do not affect a  note  already  specified.    This  property  allows
multiple tempi to exist simultaneously (see Section 8.4.4).

8.2. Default Attributes
  If  an  attribute  is  omitted, the previous one is used by default (with the
exception of the time attribute).  The default values for the first note, which
are  inherited by succeeding notes until something else is specified, are given
below in Adagio notation:

    Time           T0
    Pitch          C4
    Duration       Q
    Articulation   #100
    Loudness       LFFF
    Voice          V1
    Tempo          !TEMPO 100
    Rate           !RATE 100

Control changes (including timbre or MIDI program,  specified  by  Z)  have  no
default value and are only sent as specified in the score.

  Important:  the  rules for determining when a command will play a note are as
follows (and this has changed slightly from previous versions):

   1. If a special (!) command or nothing is specified, e.g. a blank line,
      do not play a note.

   2. If R (for ``rest'') is specified, do not play a note.

   3. Otherwise, if a pitch is specified, do play a note.

   4. Otherwise,  if no control changes (or program changes) are specified
      (so this is a command  with  non-pitch  attributes  and  no  control
      changes), do play a note.

Another  way  to  say this is ``Special commands and commands with rests (R) do
not play notes.  Otherwise, play a note if  a  pitch  is  specified  or  if  no
control is specified.''

8.3. Examples
  The  following  plays  the  first  two bars of ``Happy Birthday''.  Note that
Adagio knows nothing of bar lines, so the fact that the first  note  occurs  on
beat 3 or that the meter is three-four is of no consequence:

    *Example 1 ** Happy Birthday tune (C major)
    !TEMPO 120
    G4 I. LF
    G4 S
    A4 Q
    G4
    C5
    B4 H

The  time attribute for the first note is zero (0).  The second note will occur
a dotted eighth later, etc.  Notice that  no  timbre  or  rate  was  specified.
Adagio will provide reasonable default values of 1 and 100, respectively.

  The  following example plays the first four bars of an exercise from Bartok's
Mikrokosmos (Vol.  1, No.  12).  An extra  quarter  note  is  inserted  at  the
beginning  of  each  voice in order to allow time to change MIDI programs.  The
right hand part is played on voice (MIDI channel) 1 and the left hand  part  on
voice 2.  Notice the specification of the time attribute to indicate that voice
2 starts at time 0.  Also, default octaves are used to reduce typing.

    *Example 2 ** Bartok
    *voice 1, right hand
    R Q Z10 V1   ** extra rest for program change
    A4 H
    B Q
    C
    D H
    C
    D Q
    C
    B
    A
    B
    C
    D
    R

    *voice 2, left hand
    T0 R Q Z15 V2   ** extra rest for program change
    G3 H
    F Q
    E
    D H
    E
    D Q
    E
    F
    G
    F
    E
    D
    R

  The next  example  is  the  same  piece  expressed  in  a  different  manner,
illustrating the interaction between the !TEMPO command and the time attribute.
Recall that the time attribute is measured relative to the  time  of  the  last
!TEMPO command:

    *Example 3 ** 4 measures in 2 sections
    !Tempo 100
    *Voice 1, Measures 1 & 2
    R Q Z10 V1
    A4 H
    B Q
    C
    D H
    C

    *Voice 2, Measures 1 & 2
    T0 R Q Z15 V2
    G3 H
    F Q
    E
    D H
    E H

    !TEMPO 100
    *Voice 1, Measures 3 & 4
    * note that Z10 is still in effect for V1
    V1 D4 Q
    C
    B
    A
    B
    C
    D
    R

    *Voice 2, Measures 3 & 4
    T0 V2 D3 Q
    E
    F
    G
    F
    E
    D
    R

  The  piece  is written in 4 sections.  The first plays a rest followed by two
measures, starting at time 0.  The next section changes the time back  to  zero
and  plays  two  measures  of  the  left hand part (voice 2).  The next command
(!TEMPO 100) sets the tempo to 100 (it already is) and sets the reference  time
to  be  two  measures into the piece.  Therefore, the next note (D4) will begin
measure 3.  The D3 that begins the last group of notes has a T0  attribute,  so
it  will  also  start at measure 3.  Notice how the !TEMPO command can serve to
divide a piece into sections.

  The last example will show yet another way to express the same piece of music
using the ``Next'' attribute.  Only the first bar of music is given.

    *Example 4 ** use of the Next attribute
    !Tempo 100
    R Q Z10 V1 N0
    R Q Z15 V2

    A4 H V1 N0
    G3   V2

    B4 Q V1 N0
    F3   V2

    C4 Q V1 N0
    E3   V2

Here,  each  pair of lines represents two simultaneous notes.  The N0 attribute
forces the second line to start at the same time as  the  first  line  of  each
pair.    Because of the large intervals, octave numbers (3 and 4) are necessary
to override the default octave for these pitches.

8.4. Advanced Features
  Beyond the simple notation described  above,  Adagio  supports  a  number  of
features.  (See also the next chapter.)



8.4.1. Time Units and Resolution
                                                                             th
  The  default  time unit is 10ms (ten milliseconds or one centisecond or 100  
                                                                         th
of a second), but it is possible to change the basic unit to 1ms, or 1000    of
a second.  The time unit can be specified by:

                                        th
    !CSEC   centisecond time units = 100  
                                         th
    !MSEC   millisecond time units = 1000  

The time unit remains in effect until the next !CSEC or !MSEC command.



8.4.2. Multiple Notes Per Line
  Notes  can  be separated by commas or semicolons as well as by starting a new
line.  A comma is equivalent to typing N0 and starting a new line.    In  other
words,  the  next  note  after  a comma will start at the same time as the note
before the comma.  In general, use commas to separate the notes of a chord.

  A semicolon is equivalent to starting a new line.  In general, use semicolons
to group notes in a melody.  Here is yet another rendition of the Bartok:

    *Example 5 ** use of semicolons
    !Tempo 100
    R Q Z10 V1
    A4 H; B Q; C; D H; C; D Q; C; B; A; B; C; D; R

    T0 R Q Z15 V2
    G3 H; F Q; E; D H; E; D Q; E; F; G; F; E; D; R

This  example  is  similar  to Example 2, except semicolons are used.  Note how
semicolons make the two lines of music stand out.  The next example is  similar
to  Example  4,  except  commas  are used and four bars are notated.  The music
below is treated as a sequence of 2-note chords, with each chord on a  separate
line:

    *Example 6 ** use of commas
    !Tempo 100
    R Q Z10 V1, R Q Z15 V2
    A4 H V1, G3 V2
    B4 Q V1, F3 V2
    C4   V1, E3 V2
    D4 H V1, D3 V2
    C4   V1, E3 V2
    D4 Q V1, D3 V2
    C4   V1, E3 V2
    B4   V1, F3 V2
    A4   V1, G3 V2
    B4   V1, F3 V2
    C4   V1, E3 V2
    D4   V1, D3 V2
    R



8.4.3. Control Change Commands
  Any  control  change  can be specified using the syntax ``~n(v)'', where n is
the controller number (0 - 127), and v is the value.  In addition,  Adagio  has
some  special  syntax  for some of the commonly used control changes (note that
Pitch bend, Aftertouch, and  MIDI  Program  Change  are  technically  not  MIDI
control changes but have their own special message format and status bytes):

    K    Portamento switch

    M    Modulation wheel

    O    Aftertouch

    X    Volume

    Y    Pitch bend
    Z    Program Change


The  letter  listed  beside each control function is the Adagio command letter.
For example, M23 is the command for setting the modulation wheel to 23.  Except
for  pitch  bend,  the  portamento  switch, and MIDI Program Change, all values
range from 0 to 127.  Pitch bend is ``off'' or centered at 128, and has a range
from  0  to 255 (MIDI allows for more precision, but Adagio does not).  Turn on
portamento with K127 and off with K0.   Programs  are  numbered  1  to  128  to
correspond to synthesizer displays.

  About  volume:  Midi volume is just a control, and the Midi standard does not
say what it means. Typically it does what the volume pedal does;  that  is,  it
scales  the  amplitude  in a continuously changeable fashion. In contrast, Midi
velocity, which is controlled by the L (loudness) attribute, is part of a  Midi
note-on command and is fixed for the duration of the note. Typically, these two
ways of controlling loudness  and  amplitude  operate  independently.  In  some
low-cost  synthesizers  the  numbers  seem  to be added together internally and
volume changes are ignored after the note starts.

  About pitch bend: Midi pitch bend is a number from 0 to 16383, where 8192  is
the  center  position. To convert to Midi, Adagio simply multiplies your number
by 64, giving values from 0 to 16320. Note  that  Y128  translates  exactly  to
8192.  The meaning of pitch bend depends upon your synthesizer and its setting.
Most synthesizers let you specify a  ``pitch  bend  range.''  A  range  of  one
semitone  means that Y255 will produce a bend of approximately one semitone up,
and Y0 will bend one semitone down.  If the range is  12  semitones,  then  the
same  Y255  will  bend an octave. Typically, pitch bend is exponential, so each
increment in the pitch bend value will bend an equal number of cents in pitch.

  Control changes can be part of a note specification or independent.   In  the
following  example,  a middle C is played with a modulation wheel setting of 50
and a pitch bend of 120.  Then,  at  10  unit  intervals,  the  pitch  bend  is
decreased by 10.  The last line sets the portamento time (controller 5) to 80:

    *Example 7
    C4 LMF M50 Y120 U100 N10
    Y110 N10; Y100 N10; Y90 N10; Y80 N10
    Y70 N10; Y60 N10; Y50 N10
    ~5(80)

  See  Section 8.2 on page 28 for rules on whether or not a command will play a
note.



8.4.4. Multiple Tempi
  Writing a piece with multiple tempi requires no new commands; you  just  have
to  be  clever  in  the  use  of  Tempo and Time.  The following plays a 7 note
diatonic scale on voice 1, and a 12 note chromatic scale on voice 2:

    *Example 8 ** multiple tempi
    !TEMPO 70
    V1 C4; D; E; F; G; A; B
    T0 R N0

    !TEMPO 120
    V2 C4; CS; D; DS; E; F; FS; G; GS; A; AS; B

    !TEMPO 100
    V1 C5, V2 C5

The third line plays the 7-note diatonic scale on  voice  1.    The  next  line
contains the tricky part:  notice that the time is set back to zero, there is a
rest, and a next (N) attribute is used to specify that the  next  default  time
will  be  at the same time as the current one.  This is tricky because a !TEMPO
command cannot have a time (T0) attribute, and a T0 by itself  would  create  a
note with a duration.  T0 R N0 says: ``go to time 0, do not play a note, and do
not advance the time before the next command''.  Thus, the time of  the  !TEMPO
120  command is zero.  After the 12 note scale, the tempo is changed to 100 and
a final note is played on each voice.  A little arithmetic  will  show  that  7
notes  at  tempo 70 and 12 notes at tempo 120 each take 6 seconds, so the final
notes (C5) of each scale will happen at the same time.



8.4.5. MIDI Synchronization
  The Adagio program (but not Nyquist) can synchronize  with  external  devices
using  MIDI real time messages. Thus, Adagio has a !CLOCK command. This command
is currently of no use to Nyquist users but is documented here for completeness
(it's part of the language syntax even if it does not do anything).

  Since Adagio supports multiple tempi, and Midi clock is based on beats, it is
necessary to be explicit in the score about where the clock  should  start  and
what  is the duration of a quarter note.  The !CLOCK command in Adagio turns on
a 24 pulse-per-quarter (PPQ) clock at the current tempo and time:

    !TEMPO 100
    !CLOCK

A !CLOCK command must also be inserted for each tempo  change  that  is  to  be
reflected  in  the Midi clock.  Typically, each !TEMPO command will be followed
by a !CLOCK command.
Clock commands and thus tempo changes can take place at arbitrary times.  It is
                                         th
assumed that tempo changes on an exact 24   of a beat subdivision (for example,
exactly on a beat).  If not, the tempo change will take place  on  the  nearest
         th
exact  24    of  a  beat  subdivision.    This may be earlier or later than the
requested time.



8.4.6. System Exclusive Messages
  Adagio has a definition facility  that  makes  it  possible  to  send  system
exclusive  parameters.    Often, there are parameters on Midi synthesizers that
can only be controlled by system exclusive messages.  Examples include  the  FM
ratio and LFO rate on a DX7 synthesizer.  The following example defines a macro
for the DX7 LFO rate and then shows how the macro is used to set the  LFO  rate
for  a  B-flat  whole  note  in  the  score.   The macro definition is given in
hexadecimal, except v is replaced by the channel (voice) and %1 is replaced  by
the first parameter.  A macro is invoked by writing ``~'' followed by the macro
name and a list of parameters:

    !DEF LFO F0 43 0v 01 09 %1 F7
    Bf5 W ~LFO(25)

  In general, the !DEF command can define any single MIDI message  including  a
system  exclusive  message.  The message must be complete (including the status
byte), and each !DEF must correspond to just one message.  The symbol following
!DEF can be any name consisting of alphanumeric characters.  Following the name
is a hexadecimal string (with optional spaces), all on one line.   Embedded  in
the string may be the following special characters:

v               Insert  the  4-bit voice (MIDI channel) number.  If v occurs in
                the place of a high-order hexadecimal digit, replace v with  0v
                so  that the channel number is always placed in the low-order 4
                bits of a data byte.  In other words, v is padded if  necessary
                to fall into the low-order bits.

%n              Insert  a  data  byte  with  the  low-order 7 bits of parameter
                number n.  Parameters  are  numbered  1  through  9.    If  the
                parameter  value  is  greater than 127, the high-order bits are
                discarded.

^n              Insert a data byte with bits 7 through 13 of  parameter  number
                n.    In other words, shift the value right 7 places then clear
                all but the first 7 bits.  Note  that  14-bit  numbers  can  be
                encoded  by  referencing the same parameter twice; for example,
                %4^4 will insert the low-order followed by the high-order parts
                of parameter 4 into two successive data bytes.

  Parameters  are separated by commas, but there may be no spaces.  The maximum
number of parameters allowed is 9.  Here is an example of definitions to send a
full-resolution  pitch  bend  command and to send a system exclusive command to
change a DX7 parameter[My TX816 Owner's Manual gives an  incorrect  format  for
the  change  parameter sysex command (according to the manual, there is no data
in the message!)  I am assuming that the data should be the  last  byte  before
the  EOX and that there is no byte count.  If you are reading this, assume that
I have not tested this guess, nor have I tested this example.].

    * Define macro for pitch bend commands:
    !DEF bend Ev %1 ^1

    A ~bend(8192)  ** 8192 is "pitch bend off"

    * Change the LFO SPEED:
    *  SYSEX = F0, Yamaha = 43, Substatus/Channel = 1v,
    *  Group# = 01, Parameter# = 9, Data = 0-99, EOX = F7
    !DEF lfospeed F0 43 1v 01 09 %1 F7

    * now use the definitions:
    G4 ~bend(7567) N40
    ~lfospeed(30) N35




8.4.7. Control Ramps
  The !RAMP command can specify a smooth  control  change  from  one  value  to
another.    It consists of a specification of the starting and ending values of
some control change, a duration specifying how often to send a new value, and a
duration specifying the total length of the ramp.

    !RAMP X10 X100 Q W2
    !RAMP ~23(10) ~23(50) U20 W
    !RAMP ~lfo(15) ~lfo(35) U10

The first line says to ramp the volume control (controller number 7) from 10 to
100, changing at each quarter note for the duration of two whole  notes.    The
second  line  says  to  ramp  controller  number  23 from value 10 to value 50,
sending a new control change message every 20 time units.  The overall duration
of  the  ramp  should be equivalent to a whole note (W).  As shown in the third
line, even system exclusive messages controlled by parameters can be specified.
If the system exclusive message has more than one parameter, only one parameter
may be ``ramped''; the others must remain the same.  For example, the following
would ramp the second parameter:

    !RAMP ~mysysex(4,23,75) ~mysysex(4,100,75) U10 W

A  rather  curious  and  extreme  use of macros and ramps is illustrated in the
following example.  The noteon macro starts a note, and noteoff ends it.  Ramps
can  now be used to emit a series of notes with changing pitches or velocities.
Since Adagio has no idea that these macros are turning on notes, it  is  up  to
the programmer to turn them off!

    !DEF noteon 9v %1 %2
    !DEF noteoff 8v %1 %2
    ~noteon(48,125)
    ~noteoff(48,126)
    * turn on some notes
    !RAMP ~noteon(36,125) ~noteon(60,125) Q W NW
    * turn them off
    !RAMP ~noteoff(60,50) ~noteoff(36,50) Q W NW



8.4.8. The !End Command
  The special command !END marks the end of a score.  Everything beyond that is
ignored, for example:

    * this is a score
    C; D; E; F; G W
    !END
    since the score has ended, this text will be ignored



8.4.9. Calling C Routines
  It is possible to call C  routines  from  within  Adagio  scores  when  using
specially  linked versions, but this feature is disabled in Nyquist. The syntax
is described here for completeness.

  The !CALL command calls a C  routine  that  can  in  turn  invoke  a  complex
sequence  of  operations.    Below  is  a  call  to a trill routine, which is a
standard routine in Adagio.  The parameters are the base pitch  of  the  trill,
the  total  duration  of  the trill, the interval in semitones, the duration of
each note of the trill, and the loudness.  Notice that both numbers and  Adagio
notation can be used as parameters:

    !CALL trill(A5,W,2,S,Lmf)  T278 V1

The  parameter  list  should  have  no  spaces, and parameters are separated by
commas.  Following the close parenthesis, you may specify other attributes such
as the starting time and voice as shown in the example above.

  A  parameter  may  be  an  Adagio pitch specification, an Adagio duration, an
Adagio loudness, a number, or an ASCII character within single quotes, e.g. 'a'
is equivalent to 97 because 97 is the decimal encoding of ``a'' in ASCII.

  The  !CALL  may  be  followed by a limited set of attributes.  These are time
(T), voice (V), and next time (N).  The !CALL is made at the current time if no
time  is  specified, and the time of the next adagio command is the time of the
!CALL unless a next time is specified.  In other words, the default is N0.



8.4.10. Setting C Variables
  In addition to calling C routines, there is another way in which  scores  can
communicate  with C. As with !CALL, specific C code must be linked before these
commands can be used, and this is not supported in Nyquist.  The !SETI  command
sets  an  integer variable to a value, and the !SETV command sets an element of
an integer array.  For example, the next line sets the variable  delay  to  200
and sets transposition[5] to -4 at time 200:

    !SETI delay 200
    !SETV transposition 5 -4  T200

As  with  the  !CALL  command,  these  commands  perform  their  operations  at
particular times according to their place in the Adagio score.  This  makes  it
very  easy to implement time-varying parameters that control various aspects of
an interactive music system.
9. Linear Prediction Analysis and Synthesis
  Nyquist provides functions to perform Linear Prediction Coding (LPC) analysis
and synthesis. In simple terms, LPC analysis assumes that a sound is the result
of an all-pole filter applied to a source with a flat spectrum. LPC is good for
characterizing   the   general  spectral  shape  of  a  signal,  which  may  be
time-varying as in speech sounds.  For synthesis, any source can  be  filtered,
allowing  the  general  spectral  shape  of one signal (used in analysis) to be
applied to any source  (used  in  synthesis).  A  popular  effect  is  to  give
vowel-like  spectra  to  musical  tones,  creating  an artificial (or sometimes
natural) singing voice.

  Examples  of  LPC  analysis  and  synthesis  can  be  found   in   the   file
lpc_tutorial.htm, which is part of the standard Nyquist release.

  As  with  FFT  processing,  LPC analysis takes a sound as input and returns a
stream of frames. Frames are returned from an object using the  :next  selector
just  as  with  FFT  frames.  An  LPC frame is a list consisting of:  RMS1, the
energy of the input signal, RMS2, the energy of the residual signal,  ERR,  the
square root of RMS1/RMS2, and FILTER-COEFS, an array of filter coefficients. To
make code more readable and to avoid code dependence on the exact format  of  a
frame,   the   functions  lpc-frame-rms1,  lpc-frame-rms2,  lpc-frame-err,  and
lpc-frame-filter-coefs can be applied to  a  frame  to  obtain  the  respective
fields.

  The z transform of the filter is H(z) = 1/A(z), where A(z) is a polynomial of
the form A(z) = 1 + a z + a z + ... + a z. The FILTER-COEFS array has the  form
                     1     2           p
#(a  a    ... a  a  a ).
   p  p-1      3  2  1
  The  file  lpc.lsp defines some useful classes and functions. The file is not
automatically loaded with Nyquist, so you  must  execute  (load  "lpc")  before
using them.

9.1. LPC Classes and Functions

(make-lpanal-iterator sound framedur skiptime npoles)
     Makes an iterator object, an instance of lpanal-class,  that  returns  LPC
     frames  from  successive  frames  of  samples  in  sound. The duration (in
     seconds) of each frame is given by framedur, a FLONUM. The skip  size  (in
     seconds) between successive frames is given by skiptime, a FLONUM. Typical
     values for framedur and skiptime are 0.08 and 0.04, giving 25  frames  per
     second  and a 50% frame overlap. The number of poles is given by npoles, a
     FIXNUM. The result is an object that responds to  the  :next  selector  by
     returning  a  frame  as  described  above.  NIL  is  returned  when  sound
     terminates.  (Note that one or more of the last analysis  windows  may  be
     padded  with  zeros.  NIL  is  only returned when the corresponding window
     would begin after the termination time of the sound.)

(make-lpc-file-iterator filename)
     Another  way  to get LPC frames is to read them from a file. This function
     opens an ASCII file containing LPC frames and creates an iterator  object,
     an  instance  of  class lpc-file-class to access them. Create a file using
     save-lpc-file (see below).

(save-lpc-filelpc-iterator filename)
     Create  a  file  containing  LPC  frames.    This  file  can  be  read  by
     make-lpc-file-iterator (see above).

(show-lpc-data lpc-iterator iniframe endframe [poles?])
     Print  values  of  LPC  frames  from an LPC iterator object. The object is
     lpc-iterator,  which  is  typically  an  instance   of   lpanal-class   or
     lpc-file-class.  Frames are numbered from zero, and only files starting at
     iniframe (a FIXNUM)  and  ending  before  endframe  (also  a  FIXNUM)  are
     printed.  By default, only the values for RMS1, RMS2, and ERR are printed,
     but if optional parameter poles? is non-NIL, then the LPC coefficients are
     also printed.

(allpoles-from-lpcsnd lpc-frame)
     A single LPC frame defines a filter.  Use allpoles-from-lpc to apply  this
     filter  to  snd,  a  SOUND.  To obtain lpc-frame, a LIST containing an LPC
     frame, either send :next to an LPC iterator, or use nth-frame (see below).
     The result is a SOUND whose duration is the same as that of snd.

(lpreson snd lpc-iterator skiptime)
     Implements a time-varying all-pole filter controlled by a sequence of  LPC
     frames  from  an iterator. The SOUND to be filtered is snd, and the source
     of LPC frames is lpc-iterator, typically an instance  of  lpanal-class  or
     lpc-file-class.  The  frame  period  (in  seconds) is given by skiptime (a
     FLONUM).  This number does not have to agree with  the  skiptime  used  to
     analyze  the  frames. (Greater values will cause the filter evolution slow
     down, and smaller values will cause it to  speed  up.)  The  result  is  a
     SOUND.  The  duration  of the result is the minimum of the duration of snd
     and that of the sequence of frames.

(lpc-frame-rms1 frame)
     Get the energy of the input signal from a frame.

(lpc-frame-rms2 frame)
     Get the energy of the residual from a frame.

(lpc-frame-err frame)
     Get the square root of RMS1/RMS2 from a frame.

(lpc-frame-filter-coefs frame)
     Get the filter coefficients from a frame.

9.2. Low-level LPC Functions
  The lowest-level Nyquist functions for LPC are

   - snd-lpanal for analysis,

   - snd-allpoles, an all-pole filter with fixed coefficients, and

   - snd-lpreson, an  all-pole  filter  that  takes  frames  from  an  LPC
     iterator.

(snd-lpanal samps npoles)
     Compute an LPC frame with npoles (a FIXNUM) poles from an ARRAY of samples
     (FLONUMS).  Note  that  snd-fetch-array can be used to fetch a sequence of
     frames from a sound. Ordinarily, you should not  use  this  function.  Use
     make-lpanal-iterator instead.

(snd-allpolessnd lpc-coefs gain)
     A  fixed  all-pole  filter.  The  input  is  snd,  a  SOUND.  The   filter
     coefficients  are  given  by  lpc-coefs (an ARRAY), and the filter gain is
     given by gain, a FLONUM.  The result is a  SOUND  whose  duration  matches
     that  of  snd.   Ordinarily, you should use allpoles-from-lpc instead (see
     above).

(snd-lpreson snd lpc-iterator skiptime)
     This function is identical to lpreson (see above).
10. Developing and Debugging in Nyquist
  There are a number of tools, functions, and techniques that can help to debug
Nyquist programs. Since these are described  in  many  places  throughout  this
manual,  this  chapter  brings  together  many  suggestions  and techniques for
developing code and debugging. You really should read this chapter  before  you
spend  too  much  time  with Nyquist. Many problems that you will certainly run
into are addressed here.

10.1. Debugging
  Probably the most important debugging tool is  the  backtrace.  When  Nyquist
encounters an error, it suspends execution and prints an error message. To find
out where in the program the error occurred and how you  got  there,  start  by
typing  (bt).  This  will  print  out the last several function calls and their
arguments, which is usually sufficient to see what is going on.

  In order for (bt) to work, you must have a couple of  global  variables  set:
*tracenable*  is  ordinarily  set  to  NIL.  If it is true, then a backtrace is
automatically printed when an error occurs; *breakenable* must be set to T,  as
it  enables  the  execution  to  be  suspended when an error is encountered. If
*breakenable* is NIL (false), then execution stops when an error occurs but the
stack  is not saved and you cannot get a backtrace. Finally, bt is just a macro
to save typing.  The actual backtrace function  is  baktrace,  which  takes  an
integer argument telling how many levels to print.  All of these things are set
up by default when you start Nyquist.

  Since Nyquist sounds are executed with a lazy evaluation scheme, some  errors
are  encountered when samples are being generated.  In this case, it may not be
clear which expression is in error. Sometimes, it is best to explore a function
or  set  of  functions  by  examining intermediate results. Any expression that
yields a sound can be assigned to a variable and examined using one or more of:
s-plot,  snd-print-tree, and of course play. The snd-print-tree function prints
a lot of detail about the inner representaion of the sound. Keep in  mind  that
if  you  assign a sound to a global variable and then look at the samples (e.g.
with play or s-plot), the samples will be retained in memory. At  4  bytes  per
sample, a big sound may use all of your memory and cause a crash.

  Another  technique  is  to  use low sample rates so that it is easier to plot
results or look at samples directly. The calls:

    (set-sound-srate 100)
    (set-control-srate 100)

set the default sample rates to 100, which is too slow for  audio,  but  useful
for examining programs and results. The function

    (snd-samples sound limit)

will  convert up to limit samples from sound into a Lisp array. This is another
way to look at results in detail.

  The trace function is sometimes useful.  It prints the name of a function and
its  arguments everytimg the function is called, and the result is printed when
the function exits.  To trace the osc function, type:

    (trace osc)

and to stop tracing, type (untrace osc).

  If a variable needs a value or a function is undefined, you can fix the error
(by  setting  the  variable or loading the function definition) and keep going.
Use (co), short for (continue) to  reevaluate  the  variable  or  function  and
continue execution.

  When  you  finish  debugging a particular call, you can ``pop'' up to the top
level by typing (top), a short name for (top-level).

10.2. Useful Functions

(grindef name)
     Prints  a  formatted  listing  of a lisp function. This is often useful to
     quickly inspect a function without searching for it in  source  files.  Do
     not forget to quote the name, e.g. (grindef 'prod).

(args name)
     Similar to grindef, this function prints the arguments to a function. This
     may  be faster than looking up a function in the documentation if you just
     need a reminder. For example, (args 'lp) prints ``(LP S  C),''  which  may
     help  you  to  remember that the arguments are a sound (S) followed by the
     cutoff (C) frequency.

  The following functions are useful short-cuts that might have  been  included
in XLISP. They are so useful that they are defined as part of Nyquist.

(incf symbol)
     Increment symbol by one. This is a macro, and symbol can be anything  that
     can  be  set  by  setf. Typically, symbol is a variable: ``(incf i),'' but
     symbol can also be an array element: ``(incf (aref myarray i)).''

(decf symbol)
     Decrement symbol by one. (See incf, above.)

(push val lis)
     Push val onto lis (a Lisp list). This is a macro  that  is  equivalent  to
     writing (setf lis (cons val lis)).

(pop lis)
     Remove (pop) the first item from lis (a Lisp list). This is a  macro  that
     is  equivalent  to  writing  (setf lis (cdr lis)). Note that the remaining
     list is returned, not the head of the list that has been popped.  Retrieve
     the  head  of  the  list  (i.e.  the  top  of  the  stack) using first or,
     equivalently, car.

  The following macros are useful control constructs.

(while test stmt1 stmt2 ...)
     A  conventional  ``while''  loop.  If test is true, perform the statements
     (stmt1, stmt2, etc.) and repeat. If test is false, return. This expression
     evaluates  to  NIL  unless  the  expression (return expr) is evaluated, in
     which case the value of expr is returned.

(when test action)
     A conventional ``if-then'' statement. If test is true, action is evaluated
     and returned. Otherwise, NIL is returned. (Use if  or  cond  to  implement
     ``if-then-else'' and more complex conditional forms.

  Sometimes  it  is  important  to load files relative to the current file. For
example,  the  lib/piano.lsp  library  loads  data  files  from  the  lib/piano
directory, but how can we find out the full path of lib? The solution is:

(current-path)
     Returns the full path name of the file that is currently being loaded (see
     load). Returns NIL if no file is being loaded.

  Finally, there are some helpful math functions:

(real-randomfrom to)
     Returns a random FLONUM between from and to. (See also rrandom,  which  is
     equivalent to (real-random 0 1)).

(power x y)
     Returns x raised to the y power.
11. Xmusic and Algorithmic Composition
  Several Nyquist libraries offer support for algorithmic  composition.  Xmusic
is  a library for generating sequences and patterns of data. Included in Xmusic
is the score-gen macro which helps to generate scores from patterns.    Another
important  facility is the distributions.lsp library, containing many different
random number generators.

11.1. Xmusic Basics
  Xmusic is inspired by and based on Common Music  by  Rick  Taube.  Currently,
Xmusic  only  implements  patterns  and  some  simple  support for scores to be
realized as sound by Nyquist. In  contrast,  Common  Music  supports  MIDI  and
various  other  synthesis  languages  and  includes a graphical interface, some
visualization tools, and many other features. Common Music runs in Common  Lisp
and Scheme, but not XLISP, which is the base language for Nyquist.

  Xmusic  patterns  are  objects  that  generate data streams. For example, the
cycle-class of objects generate cyclical patterns such as "1 2 3 1 2 3  1  2  3
...",  or  "1  2  3  4  3 2 1 2 3 4 ...". Patterns can be used to specify pitch
sequences, rhythm, loudness, and other parameters.

  To use any of the Xmusic functions, you must manually load xm.lsp,  that  is,
type  (load  "xm")  to  Nyquist.  To use a pattern object, you first create the
pattern, e.g.

    (setf pitch-source (make-cycle (list c4 d4 e4 f4)))

After creating the pattern, you can access it repeatedly with next to  generate
data, e.g.

    (play (seqrep (i 13) (pluck (next pitch-source) 0.2)))

This will create a sequence of notes with the following pitches: c, d, e, f, c,
d, e, f, c, d, e, f, c. If you evaluate this again,  the  pitch  sequence  will
continue, starting on "d".

  It  is  very  important  not  to  confuse the creation of a sequence with its
access. Consider this example:

    (play (seqrep (i 13)
           (pluck (next (make-cycle (list c4 d4 e4 f4))) 0.2)))

This looks very much like the previous example, but it only  repeats  notes  on
middle-C.  The  reason  is  that  every  time pluck is evaluated, make-cycle is
called and creates a new pattern object. After the first item of the pattern is
extracted  with  next,  the  cycle  is  not  used again, and no other items are
generated.

  To summarize this important point, there are two steps to  using  a  pattern.
First,  the pattern is created and stored in a variable using setf. Second, the
pattern is accessed (multiple times) using next.

  Patterns can be nested, that is, you can write  patterns  of  patterns.    In
general,  the next function does not return patterns. Instead, if the next item
in a pattern is a (nested) pattern, next recursively gets the next item of  the
nested pattern.

  While  you  might  expect  that each call to next would advance the top-level
pattern to  the  next  item,  and  descend  recursively  if  necessary  to  the
inner-most  nesting  level, this is not how next works. Instead, next remembers
the last top-level item, and if it was a pattern, next  continues  to  generate
items  from that same inner pattern until the end of the inner pattern's period
is reached. The next paragraph explains the concept of the period.

  The data returned by a pattern  object  is  structured  into  logical  groups
called  periods.  You  can  get  an  entire period (as a list) by calling (next
pattern t). For example:

    (setf pitch-source (make-cycle (list c4 d4 e4 f4)))
    (next pitch-source t)

This prints the list (60 62 64 65), which is one period of the cycle.

  You can also get explicit markers that delineate  periods  by  calling  (send
pattern :next). In this case, the value returned is either the next item of the
pattern, or the symbol +eop+ if the end of a  period  has  been  reached.  What
determines  a  period?  This  is  up  to the specific pattern class, so see the
documentation for specifics. You can override the ``natural'' period using  the
keyword :for, e.g.

    (setf pitch-source (make-cycle (list c4 d4 e4 f4) :for 3))
    (next pitch-source t)
    (next pitch-source t)

This  prints  the  lists  (60 62 64) (65 60 62). Notice that these periods just
restructure the stream of items into groups of 3.

  Nested patterns  are  probably  easier  to  understand  by  example  than  by
specification. Here is a simple nested pattern of cycles:

    (setf cycle-1 (make-cycle '(a b c)))
    (setf cycle-2 (make-cycle '(x y z)))
    (setf cycle-3 (make-cycle (list cycle-1 cycle-2)))
    (dotimes (i 9) (format t "~A " (next cycle-3)))

This  will print "A B C X Y Z A B C". Notice that the inner-most cycles cycle-1
and cycle-2 generate a period of items before the top-level cycle-3 advances to
the next pattern.

  Before  describing  specific  pattern  classes,  there  are  several optional
parameters that apply in the creating of any pattern object. These are:

:for                The length of a  period.  This  overrides  the  default  by
                    providing  a  numerical  length. The value of this optional
                    parameter may be a pattern that  generates  a  sequence  of
                    integers  that  determine  the  length  of  each successive
                    period. A period length may not be negative, but it may  be
                    zero.

:name               A pattern object may be given a name. This is useful if the
                    :trace option is used.

:trace              If non-null, this  optional  parameter  causes  information
                    about  the  pattern  to  be  printed  each  time an item is
                    generated from the pattern.

  The built-in pattern classes are described in the following section.

11.2. Pattern Classes



11.2.1. cycle
  The cycle-class iterates repeatedly through a list of items.    For  example,
two periods of (make-cycle '(a b c)) would be (A B C) (A B C).

(make-cycle items [:for for] [:name name] [:trace trace])
     Make a cycle pattern that iterates over items. The default  period  length
     is  the  length  of  items.  (See  above for a description of the optional
     parameters.) If items is a pattern, a period of the  pattern  becomes  the
     list  from which items are generated. The list is replaced every period of
     the cycle.



11.2.2. line
  The line-class is similar to the cycle class, but when it reaches the end  of
the  list  of items, it simply repeats the last item in the list.  For example,
two periods of (make-line '(a b c)) would be (A B C) (C C C).

(make-line items [:for for] [:name name] [:trace trace])
     Make a line pattern that iterates over items. The default period length is
     the length of items. As with make-cycle, items  may  be  a  pattern.  (See
     above for a description of the optional parameters.)



11.2.3. random
  The random-class generates items at random from a list. The default selection
is uniform random with replacement, but items may be further specified  with  a
weight,  a  minimum  repetition  count, and a maximum repetition count. Weights
give the relative probability of the selection of  the  item  (with  a  default
weight  of  one).  The  minimum  count  specifies  how many times an item, once
selected at random, will be repeated. The maximum count specifies  the  maximum
number  of  times  an  item  can  be  selected  in  a row.  If an item has been
generated n times in succession, and the maximum is equal to n, then  the  item
is  disqualified  in  the  next  random  selection.  Weights (but not currently
minima and maxima) can  be  patterns.  The  patterns  (thus  the  weights)  are
recomputed every period.

(make-randomitems [:for for] [:name name] [:trace trace])
     Make a random pattern that selects from items. Any (or all) element(s)  of
     items  may  be  lists of the following form: (value [:weight weight] [:min
     mincount] [:max maxcount], where value is the  item  (or  pattern)  to  be
     generated,  weight  is  the  relative  probability of selecting this item,
     mincount is the minimum number of repetitions when this item is  selected,
     and maxcount is the maximum number of repetitions allowed before selecting
     some other item. The default period length is  the  length  of  items.  If
     items is a pattern, a period from that pattern becomes the list from which
     random selections are made, and a new list is generated every period.



11.2.4. palindrome
  The palindrome-class repeatedly traverses a list forwards and then backwards.
For  example,  two periods of (make-palindrome '(a b c)) would be (A B C C B A)
(A B C C B A). The :elide keyword parameter controls whether the  first  and/or
last elements are repeated:

    (make-palindrome '(a b c) :elide nil)
         ;; generates A B C C B A A B C C B A ...

    (make-palindrome '(a b c) :elide t)
         ;; generates A B C B A B C B ...

    (make-palindrome '(a b c) :elide :first)
         ;; generates A B C C B A B C C B ...

    (make-palindrome '(a b c) :elide :last)
         ;; generates A B C B A A B C B A ...

(make-palindrome items [:elide elide] [:for for] [:name name] [:trace trace])
     Generate  items  from  list   alternating   in-order   and   reverse-order
     sequencing. The keyword parameter elide can have the values :first, :last,
     t, or nil to control repetition of the first and last elements.  The elide
     parameter  can  also  be  a  pattern,  in which case it is evaluated every
     period. One period is one complete forward and backward traversal  of  the
     list.  If  items is a pattern, a period from that pattern becomes the list
     from which random selections are made, and a new list is  generated  every
     period.
11.2.5. heap
  The heap-class selects items in random order from a list without replacement,
which means that all items are generated once before any item is repeated.  For
example, two periods of (make-heap '(a b c)) might be (C A B) (B A C).

(make-heap items [:for for] [:name name] [:trace trace])
     Generate items randomly from list without replacement. The  period  length
     is  the length of items. If items is a pattern, a period from that pattern
     becomes the list from which random selections are made, and a new list  is
     generated every period.



11.2.6. copier
  The  copier-class  makes  copies of periods from a sub-pattern.  For example,
three periods of (make-copier (make-cycle '(a b c) :for 1) :repeat 2 :merge  t)
would be (A A) (B B) (C C). Note that entire periods (not individual items) are
repeated, so in this example the :for keyword was used to force periods  to  be
of length one so that each item is repeated by the :repeat count.

(make-copiersub-pattern [:repeat repeat] [:merge merge] [:for for] [:name name]
     [:trace trace])
     Generate a period from sub-pattern and repeat it repeat times. If merge is
     false (the default), each repetition of a period from sub-pattern  results
     in  a  period  by  default.  If  merge is true (non-null), then all repeat
     repetitions of the period are merged into one result period by default. If
     the  :for keyword is used, the same items are generated, but the items are
     grouped into periods  determined  by  the  :for  parameter.  If  the  :for
     parameter  is  a  pattern, it is evaluated every result period. The repeat
     and merge values may be patterns that return a repeat count and a  boolean
     value,  respectively.    If so, these patterns are evaluated initially and
     after each repeat  copies  are  made  (independent  of  the  :for  keyword
     parameter,  if  any).   The repeat value returned by a pattern can also be
     negative. A negative number indicates how many periods of  sub-pattern  to
     skip.  After  skipping  these  patterns,  new  repeat and merge values are
     generated.



11.2.7. accumulate
  The accumulate-class forms the sum of numbers returned  by  another  pattern.
For  example,  each  period of (make-accumulate (make-cycle '(1 2 -3))) is (1 3
0).  The default output period length is the length of the input period.

(make-accumulatesub-pattern [:for for] [:max  maximum]  [:min  minimum]  [:name
     name] [:trace trace])
     Keep a running sum of numbers generated by sub-pattern. The default period
     lengths  match  the period lengths from sub-pattern. If maximum (a pattern
     or a number) is specified,  and  the  running  sum  exceeds  maximum,  the
     running  sum  is  reset  to maximum. If minimum (a pattern or a number) is
     specified, and the running sum falls below minimum,  the  running  sum  is
     reset to minimum. If minimum is greater than maximum, the running sum will
     be set to one of the two values.



11.2.8. sum
  The sum-class forms the sum of numbers, one from each of two other  patterns.
For  example,  each period of (make-sum (make-cycle '(1 2 3)) (make-cycle '(4 5
6))) is (5 7 9).  The default output period length is the length of  the  input
period  of the first argument. Therefore, the first argument must be a pattern,
but the second argument can be a pattern or a number.

(make-sumx y [:for for] [:name name] [:trace trace])
     Form  sums  of items (which must be numbers) from pattern x and pattern or
     number y.  The default period lengths match the period lengths from x.



11.2.9. product
  The product-class forms the product of numbers, one from each  of  two  other
patterns.    For  example,  each  period of (make-product (make-cycle '(1 2 3))
(make-cycle '(4 5 6))) is (4 10 18).  The default output period length  is  the
length of the input period of the first argument. Therefore, the first argument
must be a pattern, but the second argument can be a pattern or a number.

(make-productx y [:for for] [:name name] [:trace trace])
     Form  products of items (which must be numbers) from pattern x and pattern
     or number y.  The default period lengths match the period lengths from x.



11.2.10. eval
  The eval-class evaluates an expression to produce  each  output  item.    The
default output period length is 1.

(make-evalexpr [:for for] [:name name] [:trace trace])
     Evaluate expr to generate each item. If expr is a pattern,  each  item  is
     generated by getting the next item from expr and evaluating it.



11.2.11. length
  The  length-class  generates  periods  of  a  specified  length  from another
pattern. This is similar to using the :for keyword, but for many patterns,  the
:for  parameter  alters  the  points at which other patterns are generated. For
example, if the palindrome pattern has an :elide pattern parameter,  the  value
will  be  computed every period. If there is also a :for parameter with a value
of 2, then :elide will be  recomputed  every  2  items.  In  contrast,  if  the
palindrome  (without  a  :for parameter) is embedded in a length pattern with a
lenght of 2, then the periods will all be of length 2, but the items will  come
from default periods of the palindrome, and therefore the :elide values will be
recomputed at the beginnings of default palindrome periods.

(make-length pattern length-pattern [:name name] [:trace trace])
     Make  a  pattern  of class length-class that regroups items generated by a
     pattern according to pattern lengths given by length-pattern.   Note  that
     length-pattern  is not optional: There is no default pattern length and no
     :for keyword.



11.2.12. window
  The window-class groups items from another pattern by using a sliding window.
If the skip value is 1, each output period is formed by dropping the first item
of the previous perioda and appending the next item from the pattern. The  skip
value  and  the  output  period  length  can  change every period. For a simple
example, if the period length is 3 and the skip  value  is  1,  and  the  input
pattern generates the sequence A, B, C, ..., then the output periods will be (A
B C), (B C D), (C D E), (D E F), ....

(make-window pattern length-pattern skip-pattern [:name name] [:trace trace])
     Make  a  pattern  of class window-class that regroups items generated by a
     pattern according to pattern lengths given by length-pattern and where the
     period  advances  by the number of items given by skip-pattern.  Note that
     length-pattern is not optional: There is no default pattern length and  no
     :for keyword.



11.2.13. markov
  The  markov-class  generates  items  from  a  Markov  model.  A  Markov model
generates a sequence of states according to rules which specify possible future
states  given  the most recent states in the past. For example, states might be
pitches, and each pitch might lead to a choice of pitches for the  next  state.
In the markov-class, states can be either symbols or numbers, but not arbitrary
values or patterns. This makes it easier to specify rules.    However,  symbols
can  be  mapped to arbitrary values including pattern objects, and these become
the actual generated items.    By  default,  all  future  states  are  weighted
equally,  but weights may be associated with future states. A Markov model must
be initialized with a sequence of past states using the  :past  keyword.    The
most  common  form of Markov model is a "first order Markov model" in which the
future item depends only upon one past item. However, higher order models where
the  future items depend on two or more past items are possible. A "zero-order"
Markov model, which depends on no past states, is essentially equivalent to the
random  pattern.  As an example of a first-order Markov pattern, two periods of
(make-markov '((a -> b c) (b -> c) (c -> a)) :past '(a)) might be (C A C) (A  B
C).

(make-markovrules  [:past  past]  [:produces  produces] [:for for] [:name name]
     [:trace trace])
     Generate  a  sequence  of items from a Markov process. The rules parameter
     has the form:  (prev1 prev2 ... prevn ->  next1  next2  ...  nextn)  where
     prev1 through prevn represent a sequence of most recent (past) states. The
     symbol * is treated specially: it matches any  previous  state.  If  prev1
     through  prevn (which may be just one state as in the example above) match
     the previously generated states, this rule applies. Note that  every  rule
     must  specify  the same number of previous states; this number is known as
     the order of the Markov model.  The first rule in rules  that  applies  is
     used  to  select the next state. If no rule applies, the next state is NIL
     (which is a valid state that can be used  in  rules).    Assuming  a  rule
     applies,  the  list  of possible next states is specified by next1 through
     nextn. Notice that these are alternative choices for the next state, not a
     sequence  of  future states, and each rule can have any number of choices.
     Each choice may be the state itself (a symbol or a number), or the  choice
     may  be  a  list  consisting  of the state and a weight. The weight may be
     given by a pattern, in which case the next item of the pattern is obtained
     every  time  the rule is applied. For example, this rules says that if the
     previous states were A and B, the next state can be A with a weight of 0.5
     or  C  with an implied weight of 1: (A B -> (A 0.5) C). The default length
     of the period is the length of rules. The past parameter must be provided.
     It is a list of states whose length matches the order of the Markov model.
     The keyword parameter produces may be used to map from  state  symbols  or
     numbers  to  other  values  or  patterns.  The  parameter  is  a  list  of
     alternating symbols and values. For example, to map A to 69 and B  to  71,
     use  (list 'a 69 'b 71). You can also map symbols to patterns, for example
     (list 'a (make-cycle '(57 69)) 'b (make-random '(59 71))). The  next  item
     of  the  pattern  is is generated each time the Markov model generates the
     corresponding state.  Finally, the produces keyword can  be  :eval,  which
     means  to  evaluate the Markov model state. This could be useful if states
     are Nyquist global variables such as C4, CS4, D4, ]..., which evaluate  to
     numerical values (60, 61, 62, ....

(markov-create-rulessequence order [generalize])
     Generate a set  of  rules  suitable  for  the  make-markov  function.  The
     sequence  is  a  ``typical'' sequence of states, and order is the order of
     the Markov model. It is often the case that a  sample  sequence  will  not
     have a transition from the last state to any other state, so the generated
     Markov model can reach a ``dead end'' where no rule  applies.  This  might
     lead to an infinite stream of NIL's. To avoid this, the optional parameter
     generalize can be set to t (true),  indicating  that  there  should  be  a
     fallback rule that matches any previous states and whose future states are
     weighted according  to  their  frequency  in  sequence.  For  example,  if
     sequence  contains 5 A's, 5 B's and 10 G's, the default rule will be (* ->
     (A 5) (B 5) (G 10)). This rule will be appended to the end so it will only
     apply if no other rule does.
11.3. Random Number Generators
  The distributions.lsp library implements random number generators that return
random values with various probability distributions. Without this library, you
can   generate   random  numbers  with  uniform  distributions.  In  a  uniform
distribution, all values are equally likely. To generate a  random  integer  in
some  range,  use random. To generate a real number (FLONUM) in some range, use
real-random (or rrandom if the range is 0-1). But there are  other  interesting
distributions.  For  example,  the Gaussian distribution is often used to model
real-world errors and fluctuations  where  values  are  clustered  around  some
central  value  and  large  deviations  are  more unlikely than small ones. See
Dennis Lorrain, "A Panoply of Stochastic 'Canons'," Computer Music Journal vol.
4, no. 1, 1980, pp. 53-81.

  In  most  of the random number generators described below, there are optional
parameters to indicate a maximum and/or minimum value. These  can  be  used  to
truncate  the  distribution.  For  example,  if  you  basically want a Gaussian
distribution, but you never want a value greater than 5, you can specify  5  as
the  maximum  value.    The  upper  and  lower bounds are implemented simply by
drawing a random number from the full distribution repeatedly  until  a  number
falling  into  the  desired  range  is  obtained.  Therefore,  if you select an
acceptable range that is unlikely, it may take Nyquist a long time to find each
acceptable  random number. The intended use of the upper and lower bounds is to
weed out values that are already fairly unlikely.

(linear-dist g)
     Return a FLONUM value from a linear distribution, where the probability of
     a value decreases linearly from zero to g which must be greater than zero.
     (See  Figure  7.)  The  linear  distribution  is useful for generating for
     generating time and pitch intervals.


















     Figure 7:  The Linear Distribution, g = 1.


(exponential-dist delta [high])
     Return  a  FLONUM  value  from  an  exponential  distribution. The initial
     downward slope is steeper with larger  values  of  delta,  which  must  be
     greater  than  zero.  (See  Figure  8. The optional high parameter puts an
     artificial upper bound on the return value.  The exponential  distribution
     generates  values  greater  than  0,  and  can  be  used  to generate time
     intervals. Natural random intervals such as the time intervals between the
     release  of  atomic  particles  or  the  passing  of yellow volkswagons in
     traffic have exponential distributions. The  exponential  distribution  is
     memory-less:  knowing  that  a  random  number  from  this distribution is
     greater than some value (e.g. a note duration is at least 1 second)  tells
     you  nothing  new  about  how soon the note will end. This is a continuous
     distribution, but geometric-dist (described below) implements the discrete
     form.


















     Figure 8:  The Exponential Distribution, delta = 1.


(gamma-dist nu [high])
     Return a FLONUM value from a Gamma distribution. The value is greater than
     zero,  has a mean of nu (a FIXNUM greater than zero), and a mode (peak) of
     around nu - 1.  The optional high parameter puts an artificial upper bound
     on the return value.


















     Figure 9:  The Gamma Distribution, nu = 4.


(bilateral-exponential-dist xmu tau [low] [high])
     Returns a FLONUM value from a bilateral  exponential  distribution,  where
     xmu is the center of the double exponential and tau controls the spread of
     the distribution.  A  larger  tau  gives  a  wider  distribution  (greater
     variance),  and tau must be greater than zero. The low and high parameters
     give optional artificial bounds on the minimum and maximum output  values,
     respectively.   This distribution is similar to the exponential, except it
     is centered at 0  and  can  output  negative  values  as  well.  Like  the
     exponential,  it can be used to generate time intervals; however, it might
     be necessary to add a lower bound so as not to  compute  a  negative  time
     interval.


















     Figure 10:  The Bilateral Exponential Distribution.


(cauchy-dist tau [low] [high])
     Returns a FLONUM from the Cauchy  distribution,  a  symetric  distribution
     with  a  high  peak  at  zero  and  a width (variance) that increases with
     parameter tau,  which  must  be  greater  than  zero.  The  low  and  high
     parameters  give  optional  artificial  bounds  on the minimum and maximum
     output values, respectively.


















     Figure 11:  The Cauchy Distribution, tau = 1.


(hyperbolic-cosine-dist [low] [high])
     Returns a FLONUM value from the hyperbolic cosine distribution, a symetric
     distribution with its peak at zero.  The  low  and  high  parameters  give
     optional  artificial  bounds  on  the  minimum  and maximum output values,
     respectively.


















     Figure 12:  The Hyperbolic Cosine Distribution.


(logistic-dist alpha beta [low] [high])
     Returns  a  FLONUM value from the logistic distribution, which is symetric
     about  the  mean.  The  alpha  parameter  primarily   affects   dispersion
     (variance),  with  larger  values  resulting  in values closer to the mean
     (less variance), and the beta parameter primarily influences the mean. The
     low and high parameters give optional artificial bounds on the minimum and
     maximum output values, respectively.


















     Figure 13:  The Logistic Distribution, alpha = 1, beta = 2.


(arc-sine-dist)
     Returns  a  FLONUM  value  from  the  arc sine distribution, which outputs
     values between 0 and 1. It is symetric about the mean of 1/2, but is  more
     likely to generate values closer to 0 and 1.


















     Figure 14:  The Arc Sine Distribution.


(gaussian-dist xmu sigma [low] [high])
     Returns a FLONUM value from the Gaussian or Gauss-Laplace distribution,  a
     linear  function of the normal distribution. It is symetric about the mean
     of xmu, with a standard deviation of sigma, which  must  be  greater  than
     zero.  The  low and high parameters give optional artificial bounds on the
     minimum and maximum output values, respectively.


















     Figure 15:  The Gauss-Laplace (Gaussian) Distribution, xmu = 0, sigma
     = 1.


(beta-dist a b)
     Returns a FLONUM value  from  the  Beta  distribution.  This  distribution
     outputs  values between 0 and 1, with outputs more likely to be close to 0
     or 1. The parameter a controls the height (probability) of the right  side
     of  the distribution (at 1) and b controls the height of the left side (at
     0). The distribution is symetric about 1/2 when a = b.


















     Figure 16:  The Beta Distribution, alpha = .5, beta = .25.


(bernoulli-dist px1 [x1] [x2])
     Returns either x1 (default value is 1) with probability px1 or x2 (default
     value is 0) with probability 1 - px1. The value of px1 should be between 0
     and  1.  By  convention, a result of x1 is viewed as a success while x2 is
     viewed as a failure.
























     Figure 17:  The Bernoulli Distribution, px1 = .75.


(binomial-dist n p
     Returns  a  FIXNUM  value  from  the binomial distribution, where n is the
     number of Bernoulli trials run (a FIXNUM) and  p  is  the  probability  of
     success  in  the  Bernoulli  trial (a FLONUM from 0 to 1). The mean is the
     product of n and p.
























     Figure 18:  The Binomial Distribution, n = 5, p = .5.


(geometric-dist p
     Returns  a  FIXNUM value from the geometric distribution, which is defined
     as the number of failures before a success  is  achieved  in  a  Bernoulli
     trial with probability of success p (a FLONUM from 0 to 1).
























     Figure 19:  The Geometric Distribution, p = .4.


(poisson-dist delta)
     Returns a FIXNUM value from the Poisson distribution with a mean of  delta
     (a  FIXNUM). The Poisson distribution is often used to generate a sequence
     of time intervals, resulting in random but often pleasing rhythms.
























     Figure 20:  The Poisson Distribution, delta = 3.


11.4. Score Generation and Manipulation
  A common application of pattern  generators  is  to  specify  parameters  for
notes.  (It  should  be  understood  that  ``notes''  in this context means any
Nyquist behavior, whether it represents a conventional note, an abstract  sound
object,  or even some micro-sound event that is just a low-level component of a
hierarchical sound organization. Similarly, ``score'' should be taken to mean a
specification for a sequence of these ``notes.'')  The score-gen macro (defined
by loading xm.lsp) establishes a convention for  representing  scores  and  for
generating them using patterns.

  The  timed-seq  macro,  described  in  Section 5.4, already provides a way to
represent a ``score'' as a list of expressions.  The Xmusic representation goes
a  bit  further by specifying that all notes are specified by an alternation of
keywords  and  values,  where  some  keywords  have   specific   meanings   and
interpretations.

  The basic idea of score-gen is you provide a template for notes in a score as
a set of keywords and values. For example,

    (setf pitch-pattern (make-cycle (list c4 d4 e4 f4)))
    (score-gen :dur 0.4 :name 'my-sound
             :pitch (next pitch-pattern) :score-len 9)

generates a score of 9 notes as follows:

    ((0 0 (SCORE-BEGIN-END 0 3.6))
     (0 0.4 (MY-SOUND :PITCH 60))
     (0.4 0.4 (MY-SOUND :PITCH 62))
     (0.8 0.4 (MY-SOUND :PITCH 64))
     (1.2 0.4 (MY-SOUND :PITCH 65))
     (1.6 0.4 (MY-SOUND :PITCH 60))
     (2 0.4 (MY-SOUND :PITCH 62))
     (2.4 0.4 (MY-SOUND :PITCH 64))
     (2.8 0.4 (MY-SOUND :PITCH 65))
     (3.2 0.4 (MY-SOUND :PITCH 60)))

The use of keywords like :PITCH helps to  make  scores  readable  and  easy  to
process  without specific knowledge of about the functions called in the score.
For example, one could write a transpose operation to transform all the  :pitch
parameters  in a score without having to know that pitch is the first parameter
of pluck and the second parameter of piano-note. Keyword  parameters  are  also
used  to  give  flexibility  to  note  specification with score-gen. Since this
approach requires the use of keywords, the next section is a brief  explanation
of how to define functions that use keyword parameters.



11.4.1. Keyword Parameters
  Keyword  parameters  are  parameters whose presence is indicated by a special
symbol, called a keyword, followed by the actual parameter. Keyword  parameters
may have default values that are used if no actual parameter is provided by the
caller of the function.

  To specify that a parameter is a keyword parameter, use &key to specify  that
the  following  parameters  are  keyword  parameters.  For  example,  here is a
function that accepts keyword parameters and invokes the pluck function:

    (defun k-pluck (&key pitch dur)
      (pluck pitch dur))

Now, we can call k-pluck with keyword parameters. The keywords are  simply  the
formal  parameter  names  with  a prepended colon character (:pitch and :dur in
this example), so a function call would look like:

    (pluck :key c3 :dur 3)

Usually, it is best to give keyword parameters useful default values. That way,
if  a  parameter such as :dur is missing, a reasonable default value (1) can be
used automatically. If no default value is given, the NIL will be used.  It  is
never  an  error to omit a keyword parameter, but the called function can check
to see if a keyword  parameter  was  supplied  or  not.    Default  values  are
specified by placing the parameter and the default value in parentheses:

    (defun k-pluck (&key (pitch 60) (dur 1))
      (pluck pitch dur))

Now,  we  can  call (k-pluck :pitch c3) with no duration, (k-pluck :dur 3) with
only a duration, or even (k-pluck) with no parameters.

  There is additional syntax to specify an alternate symbol to be used  as  the
keyword  and to allow the called function to determine whether or not a keyword
parameter was supplied, but these  features  are  little-used.  See  the  XLISP
manual for details.



11.4.2. Using score-gen
  The  score-gen  macro  computes  a  score  based on keyword parameters.  Some
keywords have a special meaning, while others are not  interpreted  but  merely
placed  in  the  score.  The resulting score can be synthesized using timed-seq
(see Section 5.4).

  The form of a call to score-gen is simply (score-gen :k1 e1  :k2  e2  ...  ),
where the k's are keywords and the e's are expressions. A score is generated by
evaluating the expressions once for  each  note  and  constructing  a  list  of
keyword-value  pairs.  A  number  of keywords have special interpretations. The
rules for interpreting these parameters will be explained through a set of "How
do I ..."  questions:

  How  many notes will be generated? The keyword parameter :score-len specifies
an upper bound on the number of notes.  The  keyword  :score-dur  specifies  an
upper  bound  on  the  starting time of the last note in the score. (To be more
precise, the :score-dur bound is reached when the default starting time of  the
next  note is greater than or equal to the :score-dur value. This definition is
necessary because note times are not strictly increasing.) When either bound is
reached,  score  generation  ends. At least one of these two parameters must be
specified or an error is raised. These keyword parameters  are  evaluated  just
once and are not copied into the parameter lists of generated notes.

  What  is  the duration of generated notes? The keyword :dur defaults to 1 and
specifies the nominal duration in seconds. Since the  generated  note  list  is
compatible  with  timed-seq, the starting time and duration (to be precise, the
stretch factor) are not passed  as  parameters  to  the  notes.  Instead,  they
control the Nyquist environment in which the note will be evaluated.

  What is the start time of a note? The default start time of the first note is
zero. Given a note, the default start time of the next note is the  start  time
plus  the  inter-onset  time,  which is given by the :ioi parameter. If no :ioi
parameter is specified, the inter-onset time defaults to the duration, given by
:dur.  In  all cases, the default start time of a note can be overridden by the
keyword parameter :time.

  When does the score begin and end? The behavior SCORE-BEGIN-END contains  the
beginning and ending of the score (these are used for score manipulations, e.g.
when scores are merged, their begin times can be aligned.)  When  timed-seq  is
used  to  synthesize  a score, the SCORE-BEGIN-END marker is not evaluated. The
score-gen macro inserts a ``note'' of the form (0 0 (SCORE-BEGIN-END begin-time
end-time))  at  the  time  given  by  the  :begin  keyword, with begin-time and
end-time determined by the :begin and :end keyword parameters, respectively. If
the  :begin  keyword  is  not  provided,  the score begins at zero. If the :end
keyword is not provided, the score ends at the default start time of what would
be the next note after the last note in the score (as described in the previous
paragraph). Note: if :time is used to compute note starting  times,  and  these
times  are not increasing, it is strongly advised to use :end to specify an end
time for the score, because the default end time may be anywhere in the  middle
of the generated sequence.

  What function is called to synthesize the note? The :name parameter names the
function. Like other parameters, the value can  be  any  expression,  including
something like (next fn-name-pattern), allowing function names to be recomputed
for each note. The default value is note.

  Can I make parameters depend upon the starting time or the  duration  of  the
note?  Parameter  expressions  can use the variable sg:time to access the start
time of the note, sg:ioi to access the inter-onset time, and sg:dur  to  access
the duration (stretch factor) of the note. Also, sg:count counts how many notes
have been computed so far, starting at 0. The order of computation is:  sg:time
first,  then sg:ioi and sg:dur, so for example, an expression to compute sg:dur
can depend on sg:ioi.

  Can  parameters  depend  on  each  other?  The  keyword  :pre  introduces  an
expression that is evaluated before each note, and :post provides an expression
to be evaluated after each note.  The :pre expression can assign  one  or  more
global variables which are then used in one or more expressions for parameters.

  How  do  I  debug  score-gen expressions? You can set the :trace parameter to
true (t) to enable a print statement for each generated note.

  How can I save scores generated by score-gen that  I  like?  If  the  keyword
parameter  :save is set to a symbol, the global variable named by the symbol is
set to the value of the generated sequence. Of course, the  value  returned  by
score-gen is just an ordinary list that can be saved like any other value.

  In summary, the following keywords have special interpretations in score-gen:
:begin, :end, :time, :dur, :name, :ioi, :trace, :save, :score-len,  :score-dur,
:pre,  :post.   All other keyword parameters are expressions that are evaluated
once for each note and become the parameters of the notes.
11.4.3. Score Manipulation
  Nyquist encourages the representation of music  as  executable  programs,  or
behaviors,  and  there  are  various  ways  to modify behaviors, including time
stretching, transposition, etc. An alternative to composing executable programs
is  to  manipulate scores as editable data. Each approach has its strengths and
weaknesses. This section describes  functions  intended  to  manipulate  Xmusic
scores as generated by, or at least in the form generated by, score-gen. Recall
that this means scores are lists of  events  (e.g.  notes),  where  events  are
three-element lists of the form (time duration expression, and where expression
is a standard lisp function call where all parameters are  keyword  parameters.
In  addition, the first ``note'' may be the special SCORE-BEGIN-END expression.
If this is missing, the score begins at zero and ends at the end  of  the  last
note.

  For convenience, a set of functions is offered to access properties of events
(or notes) in scores. Although lisp functions such as car, cadr, and caddr  can
be  used, code is more readable when more mnemonic functions are used to access
events.

(event-time event)
     Retrieve the time field from an event.

(event-set-time event time)
     Construct a new event where the time of event is replaced by time.

(event-dur event)
     Retrieve the duration (i.e. the stretch factor) field from an event.

(event-set-dur event dur)
     Construct a new event where the duration (or stretch factor) of  event  is
     replaced by dur.

(event-expression event)
     Retrieve the expression field from an event.

(event-set-expression event dur)
     Construct  a  new  event  where  the  expression  of  event is replaced by
     expression.

(event-end event)
     Retrieve the end time of event, its time plus its duration.

(expr-has-attr expression attribute)
     Test whether a score event expression has the given attribute.

(expr-get-attr expression attribute [default])
     Get  the  value  of  the given attribute from a score event expression. If
     attribute is not present, return default if specified, and otherwise nil.

(expr-set-attr expr attribute value)
     Construct a new expression identical to expr except that the attribute has
     value.

(event-has-attr event attribute)
     Test whether a given score event's expression has the given attribute.

(event-get-attr event attribute [default])
     Get the value of the given attribute from a score event's  expression.  If
     attribute is not present, return default if specified, and otherwise nil.

(event-set-attr event attribute value)
     Construct a new event identical to event except  that  the  attribute  has
     value.

  Functions  are  provided  to shift the starting times of notes, stretch times
and durations, stretch only durations, add an offset to  a  keyword  parameter,
scale a keyword parameter, and other manipulations. Functions are also provided
to extract ranges of notes, notes that match criteria, and to  combine  scores.
Most  of  these  functions  (listed  below  in  detail)  share a set of keyword
parameters that optionally  limit  the  range  over  which  the  transformation
operates.  The  :from-index  and  :to-index parameters specify the index of the
first note and the index of the last note to be changed. If these  numbers  are
negative,  they are offsets from the end of the score, e.g. -1 denotes the last
note of the score. The :from-time and :to-time indicate  a  range  of  starting
times of notes that will be affected by the manipulation. Only notes whose time
is greater than or equal to the from-time and strictly less  than  the  to-time
are  modified.  If  both  index  and time ranges are specified, only notes that
satisfy both constraints are selected.

(score-sorted score)
     Test if score is sorted.

(score-sort score [copy-flag])
     Sort the notes in a score into start-time order. If copy-flag is nil, this
     is a destructive operation which should only be performed if the top-level
     score list is a fresh copy that is not shared by any other variables. (The
     copy-flag  is  intended  for internal system use only.)  For the following
     operations, it is assumed that  scores  are  sorted,  and  all  operations
     return a sorted score.

(score-shift   score  offset  [:from-index  i]  [:to-index  j]  [:from-time  x]
     [:to-time y])
     Add  a constant offset to the starting time of a set of notes in score. By
     default, all notes are modified, but the range of  notes  can  be  limited
     with  the  keyword parameters. The begin time of the score is not changed,
     but the end time is increased by  offset.    The  original  score  is  not
     modified, and a new score is returned.

(score-stretch  score  factor [:dur dur-flag] [:time time-flag] [:from-index i]
     [:to-index j] [:from-time x] [:to-time y])
     Stretch  note  times  and  durations  by  factor.  The default dur-flag is
     non-null, but if dur-flag is null, the original durations are retained and
     only  times  are  stretched. Similarly, the default time-flag is non-null,
     but if time-flag is  null,  the  original  times  are  retained  and  only
     durations  are  stretched.  If  both  dur-flag and time-flag are null, the
     score is not changed. If a range of notes is specified, times  are  scaled
     within  that  range,  and  notes  after  the range are shifted so that the
     stretched region does not create a  "hole"  or  overlap  with  notes  that
     follow.  If  the  range  begins  or  ends  with a time (via :from-time and
     :to-time), time stretching takes place over the  indicated  time  interval
     independent of whether any notes are present or where they start. In other
     words, the ``rests'' are stretched along with the  notes.    The  original
     score is not modified, and a new score is returned.

(score-transpose score keyword amount [:from-index i] [:to-index j] [:from-time
     x] [:to-time y])
     For  each  note  in  the  score  and in any indicated range, if there is a
     keyword parameter matching keyword and the parameter value  is  a  number,
     increment  the parameter value by amount. For example, to tranpose up by a
     whole step, write (score-transpose 2 :pitch score). The original score  is
     not modified, and a new score is returned.

(score-scale  score keyword amount [:from-index i] [:to-index j] [:from-time x]
     [:to-time y])
     For  each  note  in  the  score  and in any indicated range, if there is a
     keyword parameter matching keyword and the parameter value  is  a  number,
     multiply  the  parameter  value  by  amount.  The  original  score  is not
     modified, and a new score is returned.

(score-sustain score  factor  [:from-index  i]  [:to-index  j]  [:from-time  x]
     [:to-time y])
     For each note in the score  and  in  any  indicated  range,  multiply  the
     duration  (stretch factor) by amount. This can be used to make notes sound
     more legato or staccato, and does not change  their  starting  times.  The
     original score is not modified, and a new score is returned.

(score-voice  score  replacement-list [:from-index i] [:to-index j] [:from-time
     x] [:to-time y])
     For  each  note  in  the  score  and  in  any indicated range, replace the
     behavior (function) name using replacement-list,  which  has  the  format:
     ((old1  new1)  (old2  new2)  ...), where oldi indicates a current behavior
     name and newi is the replacement. If oldi is *, it matches anything.   For
     example,  to  replace  my-note-1  by  trombone  and my-note-2 by horn, use
     (score-voice score '((my-note-1 trombone) (my-note-2 horn))).  To  replace
     all  instruments  with  piano,  use (score-voice score '((* piano))).  The
     original score is not modified, and a new score is returned.

(score-merge score1 score2 ...)
     Create  a  new score containing all the notes of the parameters, which are
     all scores. The resulting notes retain their original times and durations.
     The  merged  score  begin  time  is  the minimum of the begin times of the
     parameters and the merged score end time is the maximum of the  end  times
     of  the  parameters. The original scores are not modified, and a new score
     is returned.

(score-append score1 score2 ...)
     Create  a  new score containing all the notes of the parameters, which are
     all scores. The begin time of the first score is unaltered. The begin time
     of  each  other  score  is  aligned to the end time of the previous score;
     thus, scores are ``spliced'' in sequence.  The  original  scores  are  not
     modified, and a new score is returned.

(score-select  score  predicate  [:from-index  i]  [:to-index j] [:from-time x]
     [:to-time y] [:reject flag])
     Select  (or  reject) notes to form a new score. Notes are selected if they
     fall into the given ranges of index and time and they satisfy predicate, a
     function  of three parameters that is applied to the start time, duration,
     and the expression  of  the  note.  Alternatively,  predicate  may  be  t,
     indicating that all notes in range are to be selected.  The selected notes
     along with the existing score begin and end markers, are combined to  form
     a  new  score.  Alternatively,  if  the :reject parameter is non-null, the
     notes not selected form the new score (in other words the  selected  notes
     are  rejected or removed to form the new score). The original score is not
     modified, and a new score is returned.

(score-set-begin score time)
     The begin time from the score's SCORE-BEGIN-END marker is set to time. The
     original score is not modified, and a new score is returned.

(score-get-begin score)
     Return the begin time of the score.

(score-set-end score time)
     The end time from the score's SCORE-BEGIN-END marker is set to  time.  The
     original score is not modified, and a new score is returned.

(score-get-end score)
     Return the end time of the score.

(score-must-have-begin-end score)
     If  score  does  not  have  a begin and end time, construct a score with a
     SCORE-BEGIN-END expression and return it. If score already has a begin and
     end time, just return the score. The orignal score is not modified.

(score-filter-length score cutoff)
     Remove notes that extend beyond  the  cutoff  time.  This  is  similar  to
     score-select,  but  the here, events are removed when their nominal ending
     time (start time plus duration) exceeds the cutoff, whereas  the  :to-time
     parameter is compared to the note's start time.  The original score is not
     modified, and a new score is returned.

(score-repeat score n)
     Make  a  sequence  of n copies of score. Each copy is shifted to that it's
     begin time  aligns  with  the  end  time  of  the  previous  copy,  as  in
     score-append.    The  original  score  is not modified, and a new score is
     returned.

(score-stretch-to-length score length)
     Stretch  the  score so that the end time of the score is the score's begin
     time plus length.  The original score is not modified, and a new score  is
     returned.

(score-filter-overlap score)
     Remove overlapping notes (based on the  note  start  time  and  duration),
     giving  priority  to  the  positional order within the note list (which is
     also time order).  The original score is not modified, and a new score  is
     returned.

(score-print score)
     Print a score with one note per line. Returns nil.

(score-play score)
     Play  score  using  timed-seq to convert the score to a sound, and play to
     play the sound.

(score-adjacent-events score function [:from-index i] [:to-index j] [:from-time
     x] [:to-time y])
     Call (function A B C), where A, B, and C  are  consecutive  notes  in  the
     score.  The result replaces B. If the result is nil, B is deleted, and the
     next call will be (function A C D), etc. The first call  is  to  (function
     nil  A B) and the last is to (function Y Z nil). If there is just one note
     in the score, (function nil A nil) is called. Function calls are not  made
     if the note is outside of the indicated range.  This function allows notes
     and their parameters to be adjusted according to their immediate  context.
     The original score is not modified, and a new score is returned.

(score-apply  score  function  [:from-index  i]  [:to-index  j]  [:from-time x]
     [:to-time y])
     Replace  each  note  in  the  score  with the result of (function time dur
     expression), where time, dur, and expression are the time,  duration,  and
     expression  of the note.  If a range is indicated, only notes in the range
     are replaced.  The original score is not modified,  and  a  new  score  is
     returned.

(score-indexof  score  function  [:from-index  i]  [:to-index j] [:from-time x]
     [:to-time y])
     Return  the index (position) of the first score event (in range) for which
     applying function using (function time dur expression) returns true.

(score-last-indexof score function [:from-index i] [:to-index j] [:from-time x]
     [:to-time y])
     Return the index (position) of the last score event (in range)  for  which
     applying function using (function time dur expression) returns true.

(score-randomize-start  score  amt [:from-index i] [:to-index j] [:from-time x]
     [:to-time y])
     Alter the start times of notes by a random amount up to plus or minus amt.
     The original score is not modified, and a new score is returned.



11.4.4. Xmusic and Standard MIDI Files
  Nyquist has a general facility to read and write MIDI files.   You  can  even
translate  to  and from a text representation, as described in Chapter 8. It is
also useful sometimes to read notes from Standard MIDI Files into Xmusic scores
and  vice versa. At present, Xmusic only translates notes, ignoring the various
controls, program changes, pitch bends, and other messages.

  MIDI notes are translated to Xmusic score events as follows:

    (time dur (NOTE :chan channel
    :pitch keynum :vel velocity)),

where channel, keynum,  and  velocity  come  directly  from  the  MIDI  message
(channels  are  numbered starting from zero).  Note also that note-off messages
are implied by the stretch factor dur which is duration in seconds.

(score-read-smf filename)
     Read a standard MIDI file from filename. Return an Xmusic score, or nil if
     the file could not be opened. The start time is zero, and the end time  is
     the  maximum end time of all notes. A very limited interface is offered to
     extract MIDI program numbers from the file: The global variable *rslt*  is
     set  to a list of MIDI program numbers for each channel. E.g. if *rslt* is
     (0 20 77), then program for channel 0 is 0, for channel 1 is 20,  and  for
     channel  2  is  77.  Program changes were not found on other channels. The
     default program number is 0, so in this example, it is not  known  whether
     the  program  0  on  channel 0 is the result of a real MIDI program change
     command or just a default value.  If more than one program  change  exists
     on  a  channel,  the last program number is recorded and returned, so this
     information will only be completely  correct  when  the  MIDI  file  sends
     single  program  change  per  channel  before  any notes are played. This,
     however, is a fairly common practice.  Note  that  the  list  returned  as
     *rslt* can be passed to score-write-smf, described below.

(score-write-smf score filename [programs])
     Write a standard MIDI file to  filename  with  notes  in  score.  In  this
     function,  every event in the score with a :pitch attribute, regardless of
     the ``instrument'' (or function name), generates a MIDI  note,  using  the
     :chan  attribute  for  the  channel (default 0) and the :vel attribute for
     velocity  (default  100).  There  is   no   facility   (in   the   current
     implementation)   to   issue  control  changes,  but  to  allow  different
     instruments, MIDI programs may be set in two  ways.  The  simplest  is  to
     associate  programs  with  channels using the optional programs parameter,
     which is simply a list of up to 16  MIDI  program  numbers.  Corresponding
     program  change  commands  are added to the beginning of the MIDI file. If
     programs has less than 16 elements, program change commands are only  sent
     on  the  first n channels. The second way to issue MIDI program changes is
     to add a :program keyword parameter to a note in the score. Typically, the
     note  will  have a :pitch of nil so that no actual MIDI note-on message is
     generated. If program changes and notes  have  the  same  starting  times,
     their relative playback order is undefined, and the note may be cut off by
     an immediately following program change. Therefore, program changes should
     occur  slightly, e.g. 1 ms, before any notes. Program numbers and channels
     are numbered starting at zero, matching the internal MIDI  representation.
     This may be one less than displayed on MIDI hardware, sequencers, etc.



11.4.5. Workspaces
  When  working  with  scores,  you may find it necessary to save them in files
between work sessions. This is not an issue with  functions  because  they  are
normally  edited in files and loaded from them. In contrast, scores are created
as Lisp data, and unless you take care to save them,  they  will  be  destroyed
when you exit the Nyquist program.

  A  simple mechanism called a workspace has been created to manage scores (and
any other Lisp data, for that matter).  A workspace  is  just  a  set  of  lisp
global  variables.  These  variables are stored in the file workspace.lsp.  For
simplicity, there is only  one  workspace,  and  no  backups  or  versions  are
maintained,  but  the user is free to make backups and copies of workspace.lsp.
To help remember what each variable is for, you can also associate and retrieve
a text string with each variable.  The following functions manage workspaces.

  In  addition,  when  a workspace is loaded, you can request that functions be
called. For example, the workspace might  store  descriptions  of  a  graphical
interface.  When the workspace is loaded, a function might run to convert saved
data into a graphical interface. (This is how sliders are saved by the IDE.)

(add-to-workspace symbol)
     Adds  a  global variable to the workspace. The symbol should be a (quoted)
     symbol.

(save-workspace)
     All  global  variables in the workspace are saved to workspace.lsp (in the
     current directory), overwriting the previous file.

(describe symbol [description])
     If  description, a text string, is present, associate description with the
     variable named by the symbol. If symbol is not already in  the  workspace,
     it  is  added. If description is omitted, the function returns the current
     description (from a previous call) for symbol.

(add-action-to-workspacesymbol)
     Requests that the function named by symbol be called when the workspace is
     loaded (if the function is defined).

  To restore a workspace, use (load "workspace"). This restores the  values  of
the  workspace  variables  to  the values they had when save-workspace was last
called. It also restores the documentation strings, if set, by describe. If you
load  two  or  more  workspace.lsp  files,  the variables will be merged into a
single workspace. The current set of workspace variables are saved in the  list
*workspace*.  To  clear  the  workspace,  set *workspace* to nil. This does not
delete  any  variables,  but  means  that  no  variables  will  be   saved   by
save-workspace until variables are added again.

  Functions  to  be called are saved in the list *workspace-actions*.  to clear
the functions, set *workspace-actions* to nil.  Restore functions to  the  list
with add-action-to-workspace.



11.4.6. Utility Functions
  This  chapter  concludes  with details of various utility functions for score
manipulation.

(patternp expression)
     Test if expression is an Xmusic pattern.

(params-transpose params keyword amount)
     Add a  transposition  amount  to  a  score  event  parameter.  The  params
     parameter  is  a  list  of keyword/value pairs (not preceded by a function
     name).  The keyword is the keyword of the value to be altered, and  amount
     is a number to be added to the value. If no matching keyword is present in
     params, then params is  returned.  Otherwise,  a  new  parameter  list  is
     constructed and returned. The original params is not changed.

(params-scale params keyword amount)
     Scale  a  score  event  parameter   by   some   factor.   This   is   like
     params-transpose,  only using multiplication. The params list is a list of
     keyword/value pairs, keyword is the parameter keyword, and amount  is  the
     scale factor.

(interpolate x x1 y1 x2 y2)
     Linearly interpolate (or extrapolate) between points (x1, y1) and (x2, y2)
     to compute the y value corresponding to x.

(intersection a b)
     Compute the set intersection of lists a and b.

(union a b)
     Compute the set union of lists a and b.

(set-difference a b)
     Compute the set of all elements that are in a but not in b.

(subsetp a b)\
     Returns  true  iff  a  is  a  subset of b, that is, each element of a is a
     member of b.
12. Nyquist Libraries
  Nyquist is always  growing  with  new  functions.  Functions  that  are  most
fundamental  are  added to the core language. These functions are automatically
loaded when you start  Nyquist,  and  they  are  documented  in  the  preceding
chapters.  Other  functions seem less central and are implemented as lisp files
that you can load. These are called library functions, and they  are  described
here.

  To  use  a  library  function,  you  must  first load the library, e.g. (load
"pianosyn") loads the piano synthesis library. The libraries are all located in
the  lib  directory,  and  you  should therefore include this directory on your
XLISPPATH variable. (See Section 1.) Each library is documented in one  of  the
following  sections.  When  you  load the library described by the section, all
functions documented in that section become available.

12.1. Piano Synthesizer
  The piano synthesizer (library  name  is  pianosyn.lsp)  generates  realistic
piano  tones  using a multiple wavetable implementation by Zheng (Geoffrey) Hua
and Jim  Beauchamp,  University  of  Illinois.  Please  see  the  notice  about
acknowledgements  that  prints when you load the file. Further informations and
example code can be  found  in  demos/piano.htm.    There  are  several  useful
functions in this library:

(piano-note duration step dynamic)
     Synthesizes a piano tone. Duration is the duration to  the  point  of  key
     release,  after  which  there  is a rapid decay. Step is the pitch in half
     steps, and dynamic is approximately equivalent  to  a  MIDI  key  velocity
     parameter.  Use  a  value near 100 for a loud sound and near 10 for a soft
     sound.

(piano-note-2 step dynamic)
     Similar to piano-note except the duration is nominally 1.0.

(piano-midi midi-file-name)
     Use the piano synthesizer to play a MIDI file. The file name (a string) is
     given by midi-file-name.

(piano-midi2file midi-file-name sound-file-name)
     Use the piano synthesizer to play a MIDI file. The MIDI file is  given  by
     midi-file-name  and  the  (monophonic) result is written to the file named
     sound-file-name.

12.2. Dymanics Compression
  To use these functions, load the file compress.lsp. This library implements a
compressor  originally intended for noisy speech audio, but usable in a variety
of situations.  There are actually two compressors that can be used in  series.
The  first, compress, is a fairly standard one: it detects signal level with an
RMS detector and uses table-lookup to determine how much gain to place  on  the
original  signal  at  that  point.  One  bit of cleverness here is that the RMS
envelope is ``followed'' or enveloped using snd-follow, which  does  look-ahead
to anticipate peaks before they happen.

  The other interesting feature is compress-map, which builds a map in terms of
compression and expansion. For speech, the recommended procedure is  to  figure
out the noise floor on the signal you are compressing (for example, look at the
signal where the speaker is not talking).  Use a compression  map  that  leaves
the  noise  alone and boosts signals that are well above the noise floor. Alas,
the  compress-map  function  is  not  written   in   these   terms,   so   some
head-scratching is involved, but the results are quite good.

  The second compressor is called agc, and it implements automatic gain control
that keeps peaks at or below 1.0.  By  combining  compress  and  agc,  you  can
process  poorly  recorded  speech for playback on low-quality speakers in noisy
environments. The  compress  function  modulates  the  short-term  gain  to  to
minimize the total dynamic range, keeping the speech at a generally loud level,
and the agc function rides the long-term gain to set the overall level  without
clipping.

(compress-map   compress-ratio   compress-threshold  expand-ratio  expand-ratio
     [limit: limit] [transition:  transition])
     Construct  a map for the compress function. The map consists of two parts:
     a compression part and an expansion part.  The intended use is to compress
     everything  above  compress-threshold  by  compress-ratio, and to downward
     expand everything below expand-ratio by expand-ratio.  Thresholds  are  in
     dB  and  ratios are dB-per-dB.  0dB corresponds to a peak amplitude of 1.0
     or rms amplitude of 0.7 If the  input  goes  above  0dB,  the  output  can
     optionally  be limited by setting :limit (a keyword parameter) to T.  This
     effectively changes the compression ratio to infinity at 0dB.   If  :limit
     is  nil (the default), then the compression-ratio continues to apply above
     0dB.

Another keyword parameter, :transition, sets the amount  below  the  thresholds
     (in  dB)  that  a smooth transition starts. The default is 0, meaning that
     there is no smooth  transition.  The  smooth  transition  is  a  2nd-order
     polynomial  that matches the slopes of the straight-line compression curve
     and interpolates between them.

It is assumed that expand-threshold <= compress-threshold  <=  0  The  gain  is
     unity  at  0dB so if compression-ratio > 1, then gain will be greater than
     unity below 0dB.

The result returned by this function is a sound for use in the shape  function.
     The  sound  maps  input  dB to gain. Time 1.0 corresponds to 0dB, time 0.0
     corresponds to -100 dB, and time 2.0 corresponds to +100dB, so this  is  a
     100hz ``sample rate'' sound. The sound gives gain in dB.

(db-average input)
     Compute the average amplitude of input in dB.

(compress input map rise-time fall-time [lookahead])
     Compress  input  using  map,  a  compression  curve  probably generated by
     compress-map (see above). Adjustments in gain have the given rise-time and
     fall-time.  Lookahead  tells  how  far ahead to look at the signal, and is
     rise-time by default.

(agc input range rise-time fall-time [lookahead])
     An  automatic  gain  control  applied  to input. The maximum gain in dB is
     range. Peaks are attenuated to 1.0, and gain is controlled with the  given
     rise-time and fall-time. The look-ahead time default is rise-time.

12.3. Clipping Softener
  This  library,  in  soften.lsp,  was written to improve the quality of poorly
recorded speech. In recordings of speech, extreme clipping generates harsh high
frequency  noise.  This  can  sound particulary bad on small speakers that will
emphasize high  frequencies.  This  problem  can  be  ameliorated  by  low-pass
filtering  regions  where  clipping  occurs.  The  effect  is to dull the harsh
clipping. Intelligibility is not affected by much, and the result can  be  much
more  pleasant  on  the  ears. Clipping is detected simply by looking for large
signal values. Assuming 8-bit recording, this level is set to 126/127.

  The function works by cross-fading between the normal signal and  a  filtered
signal as opposed to changing filter coefficients.

(soften-clipping snd cutoff)
     Filter the loud regions of a signal  where  clipping  is  likely  to  have
     generated  additional high frequencies. The input signal is snd and cutoff
     is the filter cutoff frequency (4 kHz is recommended for speech).

12.4. Graphical Equalizer
  There's nothing really ``graphical'' about this  library  (grapheq.lsp),  but
this  is  a  common  term  for  multi-band equalizers. This implementation uses
Nyquist's  eq-band  function  to  split  the  incoming  signal  into  different
frequency  bands.  Bands  are spaced geometrically, e.g. each band could be one
octave,  meaning  that  each  successive  band  has  twice  the  bandwidth.  An
interesting  possibility  is  using  computed  control  functions  to  make the
equalization change over time.

(nband-rangeinput gains lowf highf)
     A  graphical  equalizer  applied to input (a SOUND). The gain controls and
     number of bands is given by gains, an ARRAY of SOUNDs (in other  words,  a
     Nyquist  multichannel  SOUND).  The bands are geometrically equally spaced
     from the lowest frequency lowf to the highest frequency  highf  (both  are
     FLONUMs).

(nband input gains)
     A graphical equalizer, identical to nband-range with  a  range  of  20  to
     20,000 Hz.

12.5. Sound Reversal
  The reverse.lsp library implements functions to play sounds in reverse.

(s-reverse snd)
     Reverses snd (a SOUND). Sound must be shorter than  *max-reverse-samples*,
     which  is  currently initialized to 25 million samples. Reversal allocates
     about 4 bytes per sample. This function uses XLISP  in  the  inner  sample
     loop,  so  do not be surprised if it calls the garbage collector a lot and
     runs slowly. The result starts at the starting time given by  the  current
     environment  (not  necessarily  the  starting  time  of  snd).  If snd has
     multiple channels, a multiple channel, reversed sound is returned.

s-read-reverse filename [:time-offset offset] [:srate sr] [:dur  dur]  [:nchans
     chans] [:format format] [:mode mode] [:bits n] [:swap flag]}
     This function is identical to  s-read  (see  5.5),  except  it  reads  the
     indicated samples in reverse. Like s-reverse (see above), it uses XLISP in
     the inner loop, so it is slow.  Unlike s-reverse,  s-read-reverse  uses  a
     fixed  amount  of  memory  that  is  independent  of  how many samples are
     computed. Multiple channels are handled.

12.6. Time Delay Functions
  The time-delay-fns.lsp library implements chorus, phaser, and flange effects.

(phaser snd)
     A  phaser  effect  applied  to snd (a SOUND). There are no parameters, but
     feel free to modify the source code of this one-liner.

(flange snd)
     A flange effect applied to snd. To vary the rate and other parameters, see
     the source code.

(stereo-chorussnd)
     A  chorus  effect  applied  to  snd, a SOUND (monophonic). The output is a
     stereo sound. All parameters are built-in, but see the simple source  code
     to make modifications.

(chorus snd maxdepth depth rate saturation)
     A chorus effect applied to snd. All parameters may be arrays as usual. The
     maxdepth is a FLONUM giving twice the maximum value of depth, which may be
     a FLONUM or a SOUND.  The  chorus  is  implemented  as  a  variable  delay
     modulated  by  a  sinusoid  running at rate Hz (a FLONUM). The sinusoid is
     scaled by depth and offset by maxdepth/2. The delayed signal is mixed with
     the  original,  and  saturation  gives  the fraction of the delayed signal
     (from 0 to 1) in the mix. A  reasonable  choice  of  parameter  values  is
     maxdepth = 0.05, depth = 0.025, rate = 0.5, and saturation = 0.5.

12.7. Multiple Band Effects
  The bandfx.lsp library implements several effects based on multiple frequency
bands. The idea is to separate a signal into different frequency bands, apply a
slightly  different  effect  to  each  band,  and  sum  the effected bands back
together to form the result. This file includes its own set of examples.  After
loading the file, try (f2), (f3), (f4), and (f5) to hear them.

  There is much room for expansion and experimentation with this library. Other
effects might include distortion in  certain  bands  (for  example,  there  are
commercial  effects that add distortion to low frequencies to enhance the sound
of  the  bass),  separating  bands  into  different  channels  for  stereo   or
multi-channel   effects,  adding  frequency-dependent  reverb,  and  performing
dynamic compression, limiting, or noise gate functions on each band. There  are
also  opportunities  for  cross-synthesis: using the content of bands extracted
from one signal to modify the bands of another. The simplest of these would  be
to  apply  amplitude  envelopes  of  one  sound  to  another. Please contact us
(dannenberg@cs.cmu.edu) if you are interested in working on this library.

(apply-banded-delay s lowp highp num-bands lowd highd fb wet)
     Separates  input  SOUND s into FIXNUM num-bands bands from a low frequency
     of lowp to a high frequency of  highp  (these  are  FLONUMS  that  specify
     steps, not Hz), and applies a delay to each band. The delay for the lowest
     band is given by the FLONUM lowd  (in  seconds)  and  the  delay  for  the
     highest  band is given by the FLONUM highd. The delays for other bands are
     linearly interpolated between these values. Each delay has  feedback  gain
     controlled  by  FLONUM fb. The delayed bands are scaled by FLONUM wet, and
     the original sound is scaled by 1 -  wet.  All  are  summed  to  form  the
     result, a SOUND.

(apply-banded-bass-boosts lowp highp num-bands num-boost gain)
     Applies a boost to low frequencies. Separates input SOUND  s  into  FIXNUM
     num-bands  bands from a low frequency of lowp to a high frequency of highp
     (these are FLONUMS that specify steps, not  Hz),  and  scales  the  lowest
     num-boost (a FIXNUM) bands by gain, a FLONUM. The bands are summed to form
     the result, a SOUND.

(apply-banded-treble-boosts lowp highp num-bands num-boost gain)
     Applies  a  boost to high frequencies. Separates input SOUND s into FIXNUM
     num-bands bands from a low frequency of lowp to a high frequency of  highp
     (these  are  FLONUMS  that  specify steps, not Hz), and scales the highest
     num-boost (a FIXNUM) bands by gain, a FLONUM. The bands are summed to form
     the result, a SOUND.

12.8. Granular Synthesis
  Some  granular  synthesis  functions  are implemented in the gran.lsp library
file. There are many  variations  and  control  schemes  one  could  adopt  for
granular  synthesis,  so it is impossible to create a single universal granular
synthesis function. One of the advantages of  Nyquist  is  the  integration  of
control  and  synthesis  functions, and users are encouraged to build their own
granular synthesis functions  incorporating  their  own  control  schemes.  The
gran.lsp  file  includes  many comments and is intended to be a useful starting
point.

(sf-granulate sf-granulate filename grain-dur grain-dev ioi  ioi-dev  pitch-dev
     [file-start] [file-end])
     Granular synthesis using a sound file named filename  as  the  source  for
     grains.  Each  grain  duration is the sum of grain-dur and a random number
     from 0 to grain-dev. The inter-onset interval  between  successive  grains
     (which  may  overlap)  is  the  sum  of  ioi and a random number from 0 to
     ioi-dev. Grains are resampled at a  rate  between  1  and  pitch-dev.  The
     duration  of  the result sound is determined by the stretch factor (not by
     the sound file), and grains are selected from  the  file  by  more-or-less
     stepping  through  the  file uniformly (the step size depends on the total
     number of grains needed for the output.) The optional  parameters  give  a
     starting  point  and  ending point (in seconds) from which to take samples
     from the file. To achieve a rich granular synthesis effect, it is often  a
     good  idea  to  sum four or more copies of sf-granulate together. (See the
     gran-test function in gran.lsp.)

12.9. MIDI Utilities
  The midishow.lsp library has functions that can print the  contents  fo  MIDI
files. This intended as a debugging aid.

(midi-show-file file-name)
     Print the contents of a MIDI file to the console.

(midi-show the-seq [out-file])
     Print  the  contents  of  the sequence the-seq to the file out-file (whose
     default value is the console.)

12.10. Reverberation
  The reverb.lsp library implements artificial reverberation.

(reverb snd time)
     Artificial reverberation applied to snd with a decay time of time.

12.11. DTMF Encoding
  The  dtmf.lsp  library  implements  DTMF encoding. DTMF is the ``touch tone''
code used by telephones.

(dtmf-tone key len space)
     Generate a single DTMF tone. The key parameter is either a digit (a FIXNUM
     from 0 through 9) or the atom STAR or POUND. The duration of the  done  is
     given  by  len  (a FLONUM) and the tone is followed by silence of duration
     space (a FLONUM).

(speed-dial thelist)
     Generates  a  sequence  of DTMF tones using the keys in thelist (a LIST of
     keys as described above under dtmf-tone). The duration of each tone is 0.2
     seconds,  and the space between tones is 0.1 second. Use stretch to change
     the ``dialing'' speed.

12.12. Dolby Surround(R), Stereo and Spatialization Effects
  The spatial.lsp library implements various functions for stereo  manipulation
and  spatialization.  It  also  includes  some  functions  for  Dolby Pro-Logic
panning, which encodes left, right, center, and surround channels into  stereo.
The  stereo  signal  can  then  be  played  through  a Dolby decoder to drive a
surround speaker array. This library has a somewhat simplified encoder, so  you
should  certainly  test  the  output.  Consider  using  a  high-end encoder for
critical work. There are a number of functions in spatial.lsp for testing.  See
the source code for comments about these.

(stereoizesnd)
     Convert a mono sound, snd, to stereo. Four bands of equalization and  some
     delay are used to create a stereo effect.

(widen snd amt)
     Artificially widen the stereo field  in  snd,  a  two-channel  sound.  The
     amount  of  widening  is  amt, which varies from 0 (snd is unchanged) to 1
     (maximum widening).  The amt can be a SOUND or a number.

(spansnd amt)
     Pan  the  virtual  center  channel of a stereo sound, snd, by amt, where 0
     pans all the way to the left, while 1 pans all the way to the  right.  The
     amt can be a SOUND or a number.

(swapchannelssnd)
     Swap left and right channels in snd, a stereo sound.

(prologic l c r s)
     Encode  four  monaural  SOUNDs  representing the front-left, front-center,
     front-right, and rear channels, respectively.    The  return  value  is  a
     stereo sound, which is a Dolby-encoded mix of the four input sounds.

(pl-left snd)
     Produce a Dolby-encoded (stereo) signal with snd, a SOUND, encoded as  the
     front left channel.

(pl-center snd)
     Produce a Dolby-encoded (stereo) signal with snd, a SOUND, encoded as  the
     front center channel.

(pl-right snd)
     Produce a Dolby-encoded (stereo) signal with snd, a SOUND, encoded as  the
     front right channel.

(pl-rear snd)
     Produce a Dolby-encoded (stereo) signal with snd, a SOUND, encoded as  the
     rear, or surround, channel.

(pl-pan2d snd x y)
     Comparable to Nyquist's existing pan function, pl-pan2d provides not  only
     left-to-right  panning,  but  front-to-back  panning as well. The function
     accepts three parameters: snd is the (monophonic)  input  SOUND,  x  is  a
     left-to-right  position, and y is a front-to-back position.  Both position
     parameters may be numbers or SOUNDs. An x value of 0  means  left,  and  1
     means  right.  Intermediate  values  map  linearly between these extremes.
     Similarly, a y value of 0 causes the sound to play  entirely  through  the
     front  speakers(s),  while  1 causes it to play entirely through the rear.
     Intermediate values map linearly.  Note that, although there  are  usually
     two  rear  speakers in Pro-Logic systems, they are both driven by the same
     signal. Therefore any sound that is panned totally to  the  rear  will  be
     played  over both rear speakers. For example, it is not possible to play a
     sound exclusively through the rear left speaker.

(pl-position snd x y config)
     The  position  function builds upon speaker panning to allow more abstract
     placement of sounds. Like pl-pan2d, it accepts a (monaural) input sound as
     well  as left-to-right (x) and front-to-back (y) coordinates, which may be
     FLONUMs or SOUNDs. A fourth parameter config specifies the  distance  from
     listeners  to the speakers (in meters). Current settings assume this to be
     constant for all speakers, but this assumption can be changed easily  (see
     comments  in  the  code  for  more  detail).   There are several important
     differences between pl-position and pl-pan2d. First,  pl-position  uses  a
     Cartesian coordinate system that allows x and y coordinates outside of the
     range (0, 1). This model  assumes  a  listener  position  of  (0,0).  Each
     speaker  has  a  predefined  position as well. The input sound's position,
     relative to the listener, is given by the vector (x,y).

(pl-doppler snd r)
     Pitch-shift  moving  sounds  according to the equation: fr = f0((c+vr)/c),
     where fr is the output frequency, f0 is the emitted (source) frequency,  c
     is  the  speed of sound (assumed to be 344.31 m/s), and vr is the speed at
     which the emitter approaches the receiver. (vr is the first derivative  of
     parameter r, the distance from the listener in meters.

12.13. Minimoog-inspired Synthesis
  The  moog.lsp  library  gives  the  Nyquist  user  easy access to ``classic''
synthesizer sounds through an emulation of the Minimoog  Synthesizer.    Unlike
modular  Moogs  that were very large, the Minimoog was the first successful and
commonly used portable synthesizer. The trademark filter attack was unique  and
easily recognizable. The goal of this Nyquist instrument is not only to provide
the user with default sounds, but  also  to  give  control  over  many  of  the
``knobs''  found  on the Minimoog. In this implementation, these parameters are
controlled using keywords. The input to the moog instrument is  a  user-defined
sequence of notes, durations, and articulations that simulate notes played on a
keyboard. These are  translated  into  control  voltages  that  drive  multiple
oscillators,  similar  to the Voltage Controlled Oscillator or VCO found in the
original analog Moog.

  The basic functionality of the Minimoog has been implemented,  including  the
often-used  "glide". The glide feature essentially low-pass filters the control
voltage sequence in order to create sweeps between  notes.    Figure  21  is  a
simplified schematic of the data flow in the Moog.  The control lines have been
omitted.


















     Figure 21:  System diagram for Minimoog emulator.



  The most recognizable feature of the  Minimoog  is  its  resonant  filter,  a
Four-Pole  Ladder Filter invented by Robert Moog. It is simply implemented in a
circuit with four transistors and provides an outstanding 24 dB/octave rolloff.
It is modeled here using the built-in Nyquist resonant filter.  One of the Moog
filter features is a constant Q, or center frequency to bandwidth  ratio.  This
is implemented and the user can control the Q.

  The  user  can  control many parameters using keywords. Their default values,
acceptable ranges, and descriptions are shown below. The defaults were obtained
by experimenting with the official Minimoog software synthesizer by Arturia.



12.13.1. Oscillator Parameters
  range-osc1 (2)
range-osc2 (1)
range-osc3 (3)
These  parameters  control  the  octave  of  each  oscillator.  A  value  of  1
corresponds to the octave indicated by the input note. A  value  of  3  is  two
octaves above the fundamental. The allowable range is 1 to 7.

  detun2 (-.035861)
detun3 (.0768)
Detuning  of  two oscillators adds depth to the sound. A value of 1 corresponds
to an increase of a single semitone and a -1 corresponds to  a  decrease  in  a
semitone. The range is -1 to 1.

  shape-osc1 (*saw-table*)
shape-osc2 (*saw-table*)
shape-osc3 (*saw-table*)
Oscilators  can use any wave shape. The default sawtooth waveform is a built-in
Nyquist variable. Other waveforms can be defined by the user.

  volume-osc1 (1)
volume-osc2 (1)
volume-osc3 (1)
These parameters control the relative volume of each oscillator. The  range  is
any FLONUM greater than or equal to zero.



12.13.2. Noise Parameters
  noiselevel (.05)
This  parameter  controls the relative volume of the noise source. The range is
any FLONUM greater than or equal to zero.



12.13.3. Filter Parameters
  filter-cutoff (768)
The cutoff frequency of the filter in given in Hz. The range is zero to  20,000
Hz.

  Q (2)
Q  is the ratio of center frequency to bandwidth. It is held constant by making
the bandwidth a function of frequency. The range is  any  FLONUM  greater  than
zero.

  contour (.65)
Contour  controls the range of the transient frequency sweep from a high to low
cutoff frequency when a note is played. The high frequency is  proportional  to
contour. A contour of 0 removes this sweep. The range is 0 to 1.

  filter-attack (.0001)
Filter  attack  controls  the attack time of the filter, i.e. the time to reach
the high cutoff frequency. The range is any FLONUM greater than zero (seconds).

  filter-decay (.5)
Filter decay controls the decay time of the filter, i.e. the time of the  sweep
from  the  high  to  low cutoff frequency. The range is any FLONUM greater than
zero (seconds).

  filter-sustain (.8)
Filter sustain controls the percentage of the filter cutoff frequency that  the
filter settles on following the sweep. The range is 0 to 1.



12.13.4. Amplitude Parameters
  amp-attack (.01)
This  parameter  controls  the amplitude envelope attack time, i.e. the time to
reach maximum amplitude. The range is any FLONUM greater than zero (seconds).

  amp-decay (1)
This parameter controls the  amplitude  envelope  decay  time,  i.e.  the  time
between  the  maximum and sustain volumes. The range is any FLONUM greater than
zero (seconds).

  amp-sustain (1)
This parameter controls the amplitude envelope sustain volume,  a  fraction  of
the maximum. The range is 0 to 1.

  amp-release (0)
This  parameter  controls the amplitude envelope release time, i.e. the time it
takes between the sustain volume and 0  once  the  note  ends.    The  duration
controls  the  overall  length  of  the  sound. The range of amp-release is any
FLONUM greater than zero (seconds).



12.13.5. Other Parameters
  glide (0)
Glide controls the low-pass filter on the control  voltages.  This  models  the
glide  knob  on  a  Minimoog.  A  higher  value  corresponds  to a lower cutoff
frequency and hence a longer "glide" between notes. A value of 0 corresponds to
no glide. The range is zero to 10.



12.13.6. Input Format
  A  single  note  or  a series of notes can be input to the Moog instrument by
defining a list with the following format:

    (list (list frequency duration articulation) ... )

where frequency is a FLONUM in steps, duration is the duration of each note  in
seconds  (regardless of the release time of the amplifier), and articulation is
a percentage of the duration that a sound  will  be  played,  representing  the
amount  of  time  that a key is pressed. The filter and amplitude envelopes are
only triggered if a note is played when the articulation of the  previous  note
is  less than 1, or a key is not down at the same time. This Moog instrument is
a monophonic instrument, so only one note can sound  at  a  time.  The  release
section  of  the amplifier is triggered when the articulation is less than 1 at
the time (duration * articulation).



12.13.7. Sample Code/Sounds
  Sound 1 (default parameters):

    (setf s '((24 .5 .99)(26 .5 .99)(28 .5 .99)(29 .5 .99)(31 2 1)))
    (play (moog s))


  Sound 2 (articulation, with amplitude release):

    (setf s '((24 .5 .5)(26 .5 1)(28 .5 .25)(29 .5 1)(31 1 .8)))
    (play (moog s :amp-release .2))


  Sound 3 (glide):

    (setf s '((24 .5 .5)(38 .5 1)(40 .5 .25)
              (53 .5 1)(55 2 1)(31 2 .8)(36 2 .8)))
    (play (moog s :amp-release .2 :glide .5))


  Sound 4 (keyword parameters): Filter attack and decay  are  purposely  longer
than notes being played with articulation equal to 1.

    (setf s '((20 .5 1)(27 .5 1)(26 .5 1)(21 .5 1)
              (20 .5 1)(27 .5 1)(26 .5 1)(21 .5 1)))
    (play (moog s :shape-osc1 *tri-table* :shape-osc2 *tri-table*
                  :filter-attack 2 :filter-decay 2
                  :filter-cutoff 300 :contour .8 :glide .2 :Q 8))


  Sound  5:  This  example  illustrates  the ability to completely define a new
synthesizer with different parameters creating a drastically  different  sound.
Sine waves are used for wavetables. There is a high value for glide.

    (defun my-moog (freq) (moog freq
      :range-osc1 3 :range-osc2 2 :range-osc3 4
      :detun2 -.043155 :detun3 .015016
      :noiselevel 0
      :filter-cutoff 400 :Q .1 :contour .0000001
      :filter-attack 0 :filter-decay .01 :filter-sustain 1
      :shape-osc1 *sine-table* :shape-osc2 *sine-table*
      :shape-osc3 *sine-table* :volume-osc1 1 :volume-osc2 1
      :volume-osc3 .1 :amp-attack .1 :amp-decay 0
      :amp-sustain 1 :amp-release .3 :glide 2))

    (setf s '((80 .4 .75)(28 .2 1)(70 .5 1)(38 1 .5)))
    (play (my-moog s))


  Sound 6: This example has another variation on the default parameters.
    (setf s '((24 .5 .99)(26 .5 .99)(28 .5 .99)(29 .5 .99)(31 2 1)))
    (play (moog s :shape-osc1 *tri-table* :shape-osc2 *tri-table*
                  :filter-attack .5 :contour .5))
I. Extending Nyquist
  WARNING:    Nyquist sound functions look almost like a human wrote them; they
even have a fair number of comments  for  human  readers.    Don't  be  fooled:
virtually  all  Nyquist  functions are written by a special translator.  If you
try to write a new function by hand, you will probably not succeed, and even if
you do, you will waste a great deal of time.  (End of Warning.)

I.1. Translating Descriptions to C Code
  The  translator  code used to extend Nyquist resides in the trnsrc directory.
This directory also contains a special init.lsp,  so  if  you  start  XLisp  or
Nyquist  in  this directory, it will automatically read init.lsp, which in turn
will load the translator code (which resides in several files).

  Also in the trnsrc directory are a number of .alg files,  which  contain  the
source  code  for  the  translator (more on these will follow), and a number of
corresponding .h and .c files.

  To translate a .alg file to .c and .h files, you start XLisp  or  Nyquist  in
the trnsrc directory and type

    (translate "prod")

where  "prod"  should really be replaced by the filename (without a suffix) you
want to translate.  Be sure you have a saved, working copy of Nyquist or  Xlisp
before you recompile!

  Note:  On  the  Macintosh,  just run Nyquist out of the runtime directory and
then use the Load menu command to load  init.lsp  from  the  trnsrc  directory.
This  will  load the translation code and change Nyquist's current directory to
trnsrc so that commands like (translate "prod") will work.

I.2. Rebuilding Nyquist
  After generating prod.c and prod.h, you need to recompile Nyquist.  For  Unix
systems,  you  will  want to generate a new Makefile.  Modify transfiles.lsp in
your main Nyquist directory,  run  Xlisp  or  Nyquist  and  load  makefile.lsp.
Follow  the  instructions to set your machine type, etc., and execute (makesrc)
and (makefile).

I.3. Accessing the New Function
  The new Lisp function will generally  be  named  with  a  snd-  prefix,  e.g.
snd-prod.    You  can  test  this  by  running Nyquist.  Debugging is usually a
combination of calling the  code  from  within  the  interpreter,  reading  the
generated code when things go wrong, and using a C debugger to step through the
inner loop of the generated code.  An approach I like is  to  set  the  default
sample  rate  to 10 hertz.  Then, a one-second sound has only 10 samples, which
are easy to print and study on a text console.

  For some functions, you must write some Lisp code to impose ordinary  Nyquist
behaviors  such  as  stretching  and time shifting.  A good approach is to find
some structurally similar functions and see how they are implemented.  Most  of
the Lisp code for Nyquist is in nyquist.lsp.

  Finally,  do  not forget to write up some documentation.  Also, contributions
are welcome.  Send your .alg file, documentation, Lisp  support  functions  for
nyquist.lsp,  and  examples  or test programs to rbd@cs.cmu.edu.  I will either
put them in the next release or make them available at a public ftp site.

I.4. Why Translation?
  Many of the Nyquist signal processing operations are  similar  in  form,  but
they  differ in details. This code is complicated by many factors: Nyquist uses
lazy evaluation, so the operator must check  to  see  that  input  samples  are
available  before  trying  to  access  them. Nyquist signals can have different
sample rates, different block sizes, different block boundaries, and  different
start  times,  all of which must be taken into account.  The number of software
tests is enormous. (This may sound like a lot of overhead, but the overhead  is
amortized  over  many  iterations  of  the inner loop. Of course setting up the
inner loop to run efficiently is one more programming task.)

  The main idea behind the translation is that all of the checks and setup code
are  similar  and  relatively easy to generate automatically. Programmers often
use macros for this sort of task, but the C macro processor is too limited  for
the  complex  translation required here. To tell the translator how to generate
code, you write .alg files, which provide many details about the operation in a
declarative style.  For example, the code generator can make some optimizations
if you declare that two input signals are commutative (they  can  be  exchanged
with  one  another).  The main part of the .alg file is the inner loop which is
the heart of the signal processing code.

I.5. Writing a .alg File
  To give you some idea how functions are specified, here is the  specification
for snd-prod, which generates over 250 lines of C code:

    (PROD-ALG
      (NAME "prod")
      (ARGUMENTS ("sound_type" "s1") ("sound_type" "s2"))
      (START (MAX s1 s2))
      (COMMUTATIVE (s1 s2))
      (INNER-LOOP "output = s1 * s2")
      (LINEAR s1 s2)
      (TERMINATE (MIN s1 s2))
      (LOGICAL-STOP (MIN s1 s2))
    )

A .alg file is always of the form:

    (name
      (attribute value)
      (attribute value)
      ...
    )

There  should  be just one of these algorithms descriptions per file.  The name
field is arbitrary: it is a Lisp symbol whose property list is used to save the
following  attribute/value  pairs.   There are many attributes described below.
For more examples, see the .alg files in the trnsrc directory.

  Understanding what  the  attributes  do  is  not  easy,  so  here  are  three
recommendations  for  implementors.    First,  if  there is an existing Nyquist
operator that is structurally similar to something you want to implement,  make
a  copy  of the corresponding .alg file and work from there. In some cases, you
can merely rename the parameters and substitute a new inner loop.  Second, read
the  generated  code, especially the generated inner loop.  It may not all make
sense, but sometimes you can spot obvious errors and work your way back to  the
error  in  the .alg file.  Third, if you know where something bad is generated,
see if you can find where the code is generated.  (The code generator files are
listed in init.lsp.)  This code is poorly written and poorly documented, but in
some cases it is fairly straightforward to determine what attribute in the .alg
file is responsible for the erroneous output.

I.6. Attributes
  Here  are  the attributes used for code generation. Attributes and values may
be specified in any order.

(NAME "string") specifies a base name for many identifiers.  In particular, the
                generated  filenames  will  be  string.c  and string.h, and the
                XLisp function generated will be snd-string.

(ARGUMENTS arglist)
                describes  the  arguments  to be passed from XLisp. Arglist has
                the form: (type1 name1) (type2 name2) ..., where type and  name
                are strings in double quotes, e.g. ("sound_type" "s") specifies
                a SOUND parameter named s.  Note that arglist is not surrounded
                by  parentheses.    As seen in this example, the type names and
                parameter names are C identifiers.  Since  the  parameters  are
                passed  in  from  XLisp,  they must be chosen from a restricted
                set.    Valid  type  names  are:   "sound_type",   "rate_type",
                "double", "long", "string", and "LVAL".

(STATE statelist)
                describes additional state (variables) needed  to  perform  the
                computation.    A  statelist  is  similar  to  an  arglist (see
                ARGUMENTS above), and has the form: (type1 name1 init1  [TEMP])
                (type2  name2 init2 [TEMP]) ....  The types and names are as in
                arglist, and the  "inits"  are  double-quoted  initial  values.
                Initial  values  may be any C expression.  State is initialized
                in the order implied by statelist when the operation  is  first
                called  from  XLisp.  If TEMP is omitted the state is preserved
                in  a  structure  until  the   sound   computation   completes.
                Otherwise,   the   state   variable   only   exists   at  state
                initialization time.

(INNER-LOOP innerloop-code)
                describes the inner loop, written as C code. The innerloop-code
                is in double quotes, and may extend over multiple  lines.    To
                make  generated  code  extra-beautiful,  prefix  each  line  of
                innerloop-code with 12 spaces.  Temporary variables should  not
                be  declared  at  the  beginning  of  innerloop-code.  Use  the
                INNER-LOOP-LOCALS attribute instead.    Within  innerloop-code,
                each ARGUMENT of type sound_type must be referenced exactly one
                time. If you need to use a signal value twice, assign  it  once
                to  a  temporary  and  use the temporary twice.  The inner loop
                must also assign one time to the psuedo-variable output.    The
                model  here  is  that  the name of a sound argument denotes the
                value of the corresponding signal at the current output  sample
                time.   The inner loop code will be called once for each output
                sample.  In practice, the code generator will  substitute  some
                expression   for   each  signal  name.  For  example,  prod.alg
                specifies

                    (INNER-LOOP "output = s1 * s2")

                (s1 and s2 are ARGUMENTS.)  This expands to the following inner
                loop in prod.c:

                    *out_ptr_reg++ = *s1_ptr_reg++ * *s2_ptr_reg++;

                In  cases  where  arguments have different sample rates, sample
                interpolation is in-lined, and the  expressions  can  get  very
                complex.  The  translator is currently very simple-minded about
                substituting access code in the place of parameter  names,  and
                this  is a frequent source of bugs.  Simple string substitution
                is performed, so you must not use a  parameter  or  state  name
                that  is  a  substring  of  another.  For example, if two sound
                parameters were named s and s2, the translator might substitute
                for  ``s''  in  two  places  rather  than one.  If this problem
                occurs, you will almost  certainly  get  a  C  compiler  syntax
                error.    The fix is to use ``more unique'' parameter and state
                variable names.

(INNER-LOOP-LOCALS "innerloop-code")
                The  innerloop-code  contains C declarations of local variables
                set and referenced in the inner loop.

(SAMPLE-RATE "expr")
                specifies the output sample rate; expr can be any C expression,
                including a parameter from the ARGUMENTS  list.  You  can  also
                write  (SAMPLE-RATE  (MAX  name1  name2  ...))  where names are
                unquoted names of arguments.

(SUPPORT-HEADER "c-code")
                specifies  arbitrary  C code to be inserted in the generated .h
                file.  The  code   typically   contains   auxiliarly   function
                declarations and definitions of constants.

(SUPPORT-FUNCTIONS "c-code")
                specifies arbitrary C code to be inserted in the  generated  .c
                file.  The  code  typically  contains  auxiliarly functions and
                definitions of constants.

(FINALIZATION "c-code")
                specifies  code  to  execute  when  the  sound  has  been fully
                computed and the state variables are about to be  decallocated.
                This is the place to deallocate buffer memory, etc.

(CONSTANT "name1" "name2" ...)
                specifies state variables that do not change value in the inner
                loop.   The values of state variables are loaded into registers
                before entering the inner loop so  that  access  will  be  fast
                within the loop.  On exiting the inner loop, the final register
                values are preserved in a ``suspension'' structure.   If  state
                values   do  not  change  in  the  inner  loop,  this  CONSTANT
                declaration  can  eliminate  the  overhead  of  storing   these
                registers.

(START spec)    specifies  when  the output sound should start (a sound is zero
                and no processing is done before the start time). The spec  can
                take  several forms: (MIN name1 name2 ...) means the start time
                is the minimum of the  start  times  of  input  signals  name1,
                name2, ....  Note that these names are not quoted.

(TERMINATE spec)
                specifies when the output sound terminates  (a  sound  is  zero
                after  this termination time and no more samples are computed).
                The spec can take several forms: (MIN name1  name2  ...)  means
                the  terminate  time  is  the minimum of the terminate times of
                input arguments name1, name2, ....  Note that these  names  are
                not  quoted.  To terminate at the time of a single argument s1,
                specify (MIN s1).  To terminate after a specific duration,  use
                (AFTER  "c-expr"),  where c-expr is a C variable or expression.
                To terminate at a particular time, use (AT "c-expr").  spec may
                also be COMPUTED, which means to use the maximum sample rate of
                any input signal.

(LOGICAL-STOP spec)
                specifies the logical stop time of the output sound.  This spec
                is just like  the  one  for  TERMINATE.    If  no  LOGICAL-STOP
                attribute  is  present, the logical stop will coincide with the
                terminate time.

(ALWAYS-SCALE name1 name2 ...)
                says  that  the  named  sound  arguments (not in quotes) should
                always be multiplied by a scale factor.  This is  a  space-time
                tradeoff.  When  Nyquist sounds are scaled, the scale factor is
                merely stored in a structure.  It is the responsibility of  the
                user  of  the  samples to actually scale them (unless the scale
                factor is exactly 1.0).  The default is to generate  code  with
                and  without  scaling and to select the appropriate code at run
                                                                              N
                time.  If there are N signal  inputs,  this  will  generate  2 
                versions  of  the  code.  To avoid this code explosion, use the
                ALWAYS-SCALE attribute.

(INLINE-INTERPOLATION T)
                specifies  that  sample  rate interpolation should be performed
                in-line in the inner loop. There are two forms of  sample  rate
                interpolation.  One is intended for use when the rate change is
                large and many points will be interpolated.  This form  uses  a
                divide  instruction  and some setup at the low sample rate, but
                the inner loop  overhead  is  just  an  add.  The  other  form,
                intended   for  less  drastic  sample  rate  changes,  performs
                interpolation with 2 multiplies and several adds per sample  at
                the  high  sample  rate.  Nyquist generates various inner loops
                and  selects   the   appropriate   one   at   run-time.      If
                INLINE-INTERPOLATION  is  not  set,  then  much  less  code  is
                generated  and  interpolation  is  performed  as  necessary  by
                instantiating a separate signal processing operation.

(STEP-FUNCTION name1 name2 ...)
                Normally all argument signals are linearly interpolated to  the
                output sample rate.  The linear interpolation can be turned off
                with this attribute. This is  used,  for  example,  in  Nyquist
                variable  filters  so  that filter coefficients are computed at
                low sample rates.  In fact, this attribute was  added  for  the
                special case of filters.

(DEPENDS spec1 spec2 ...)
                Specifies dependencies.  This attribute was also introduced  to
                handle  the  case  of  filter  coefficients (but may have other
                applications.)  Use it when a state variable is a function of a
                potentially  low-sample-rate  input  where  the input is in the
                STEP-FUNCTION list.  Consider a filter coefficient that depends
                upon an input signal such as bandwidth.  In this case, you want
                to compute the filter coefficient only when  the  input  signal
                changes rather than every output sample, since output may occur
                at a much higher sample rate.  A spec is of the form

                    ("name" "arg" "expr" [TEMP "type"])

                which is interpreted as follows: name depends  upon  arg;  when
                arg  changes,  recompute  expr  and assign it to name. The name
                must be declared as a STATE variable unless TEMP is present, in
                which  case  name  is not preserved and is used only to compute
                other state.  Variables are updated in the order of the DEPENDS
                list.

(FORCE-INTO-REGISTER name1 name2 ...)
                causes name1, name2, ... to be  loaded  into  registers  before
                entering  the inner loop.  If the inner loop references a state
                variable or argument,  this  happens  automatically.  Use  this
                attribute  only  if  references  are  ``hidden'' in a #define'd
                macro or referenced in a DEPENDS specification.

(NOT-REGISTER name1 name2 ...)
                specifies  state  and  arguments that should not be loaded into
                registers before entering an inner loop.  This is sometimes  an
                optimization for infrequently accessed state.

(NOT-IN-INNER-LOOP "name1" "name2" ...)
                says that certain arguments are not used  in  the  inner  loop.
                Nyquist  assumes  all  arguments are used in the inner loop, so
                specify them here if not.  For example, tables are passed  into
                functions   as   sounds,   but   these   sounds  are  not  read
                sample-by-sample in the inner loop, so they  should  be  listed
                here.

(MAINTAIN ("name1" "expr1") ("name2" "expr2") ...  )
                Sometimes the IBM XLC compiler generates better loop code if  a
                variable  referenced  in  the loop is not referenced outside of
                the loop after the loop exit.    Technically,  optimization  is
                better when variables are dead upon loop exit. Sometimes, there
                is an efficient way to compute  the  final  value  of  a  state
                variable  without  actually  referencing  it, in which case the
                variable and the computation method are given as a pair in  the
                MAINTAIN  attribute.    This suppresses a store of the value of
                the named variable, making it a dead variable.  Where the store
                would have been, the expression is computed and assigned to the
                named  variable.    See  partial.alg  for  an  example.    This
                optimization is never necessary and is only for fine-tuning.

(LINEAR name1 name2 ...)
                specifies that named arguments (without quotes) are linear with
                respect  to  the  output.  What this really means is that it is
                numerically OK to eliminate  a  scale  factor  from  the  named
                argument  and store it in the output sound descriptor, avoiding
                a potential multiply in this inner loop.    For  example,  both
                arguments  to  snd-prod (signal multiplication) are ``linear.''
                The inner loop has a single multiplication operator to multiply
                samples  vs.  a potential 3 multiplies if each sample were also
                scaled.  To handle scale factors  on  the  input  signals,  the
                scale  factors  are  automatically  multiplied  and the product
                becomes the scale  factor  of  the  resulting  output.    (This
                effectively  ``passes the buck'' to some other, or perhaps more
                than one, signal  processing  function,  which  is  not  always
                optimal.  On  the  other hand, it works great if you multiply a
                number of scaled signals together: all the  scale  factors  are
                ultimately handled with a single multiply.)

(INTERNAL-SCALING name1 name2 ...)
                indicates that scaling is handled in code that is  hidden  from
                the  code  generator  for  name1,  name2,  ..., which are sound
                arguments. Although it is the responsibility of the  reader  of
                samples  to apply any given scale factor, sometimes scaling can
                be had for free.  For example, the snd-recip operation computes
                the  reciprocal  of  the input samples by peforming a division.
                The simple approach would be to specify an inner loop of output
                =  1.0/s1,  where  s1  is  the input.  With scaling, this would
                generate an inner loop something like this:

                    *output++ = 1.0 / (s1_scale_factor * *s1++);

                but a much better approach would be the following:

                    *output++ = my_scale_factor / *s1++

                where  my_scale_factor  is  initialized  to  1.0  /  s1->scale.
                Working  backward from the desired inner loop to the .alg inner
                loop specification, a first attempt might be to specify:

                    (INNER-LOOP "output = my_scale_factor / s1")

                but this will generate the following:

                    *output++=my_scale_factor/(s1_scale_factor * *s1++);

                Since the code generator does not know that scaling is  handled
                elsewhere,  the  scaling is done twice!  The solution is to put
                s1 in the INTERNAL-SCALING list, which essentially means ``I've
                already  incorporated  scaling  into the algorithm, so suppress
                the multiplication by a scale factor.''

(COMMUTATIVE (name1 name2 ...))
                specifies   that   the   results   will   not  be  affected  by
                interchanging any of the listed arguments.  When arguments  are
                commutative,   Nyquist   rearranges   them   at  run-time  into
                decreasing order of sample rates.  If interpolation is in-line,
                this  can  dramatically  reduce the amount of code generated to
                handle all the different cases.  The prime example is prod.alg.

(TYPE-CHECK "code")
                specifies  checking  code  to  be  inserted after argument type
                checking at  initialization  time.  See  downproto.alg  for  an
                example  where  a  check  is  made to guarantee that the output
                sample  rate  is  not  greater  than  the  input  sample  rate.
                Otherwise an error is raised.

I.7. Generated Names
  The  resulting .c file defines a number of procedures. The procedures that do
actual sample computation  are  named  something  like  name_interp-spec_FETCH,
where  name  is  the  NAME  attribute from the .alg file, and interp-spec is an
interpolation specification composed of a string of the following  letters:  n,
s,  i,  and  r.    One letter corresponds to each sound argument, indicating no
interpolation (r), scaling only (s), ordinary linear interpolation with scaling
(i), and ramp (incremental) interpolation with scaling (r).  The code generator
determines all the combinations of n, s,  i,  and  r  that  are  necessary  and
generates a separate fetch function for each.

  Another  function  is  name_toss_fetch,  which  is called when sounds are not
time-aligned and some initial samples  must  be  discarded  from  one  or  more
inputs.

  The  function  that  creates  a  sound is snd_make_name.  This is where state
allocation and initialization takes  place.    The  proper  fetch  function  is
selected  based  on  the sample rates and scale factors of the sound arguments,
and a sound_type is returned.

  Since Nyquist is a functional language, sound  operations  are  not  normally
allowed  to  modify  their  arguments  through  side  effects, but even reading
samples from a sound_type causes side effects. To hide these from  the  Nyquist
programmer,  sound_type  arguments  are  first copied (this only copies a small
structure. The samples themselves are on a shared list). The function  snd_name
performs  the  necessary  copies  and  calls snd_make_name.  It is the snd_name
function that is called by XLisp.  The XLisp name for the function is SND-NAME.
Notice  that  the underscore in C is converted to a dash in XLisp.  Also, XLisp
converts identifiers to upper case when they are read, so normally,  you  would
type snd-name to call the function.

I.8. Scalar Arguments
  If you want the option of passing either a number (scalar) or a signal as one
of the arguments, you have two choices, neither of which is automated.   Choice
1  is  to  coerce  the  constant  into  a signal from within XLisp.  The naming
convention would be to DEFUN a new function named NAME or S-NAME  for  ordinary
use.    The  NAME  function  tests  the arguments using XLisp functions such as
TYPE-OF, NUMBERP, and SOUNDP.  Any number is converted to a SOUND,  e.g.  using
CONST.   Then SND-NAME is called with all sound arguments.  The disadvantage of
this scheme is that scalars are expanded into a sample stream, which is  slower
than having a special inner loop where the scalar is simply kept in a register,
avoiding loads, stores, and addressing overhead.

  Choice 2 is to generate a different sound operator for each case.  The naming
convention  here  is  to  append  a  string of c's and v's, indicating constant
(scalar) or variable (signal) inputs.  For example, the reson operator comes in
four  variations:  reson,  resoncv,  resonvc, and resonvv.  The resonvc version
implements a resonating filter with a variable center frequency (a sound  type)
and  a  constant  bandwidth  (a  FLONUM).   The RESON function in Nyquist is an
ordinary  Lisp  function  that  checks  types  and  calls  one  of   SND-RESON,
SND-RESONCV, SND-RESONVC, or SND-RESONVV.

  Since   each   of   these   SND-  functions  performs  further  selection  of
implementation based on sample rates and the need for  scaling,  there  are  25
different  functions  for computing RESON!  So far, however, Nyquist is smaller
than Common Lisp and it's about half the size of Microsoft  Word.    Hopefully,
exponential  growth  in  memory  density  will outpace linear (as a function of
programming effort) growth of Nyquist.
II. Open Sound Control and Nyquist
  Open Sound Control (OSC) is a simple protocol for communicating music control
parameters   between  software  applications  and  across  networks.  For  more
information, see http://www.cnmat.berkeley.edu/OpenSoundControl/.  The  Nyquist
implementation  of  Open Sound Control is simple: an array of floats can be set
by OSC messages and read by Nyquist functions. That is about all  there  is  to
it.

  Note:  Open  Sound Control must be enabled by calling (osc-enable t). If this
fails under Windows, see the installation instructions regarding SystemRoot.

  To control something in (near) real-time, you need to access a  slider  value
as  if  it  a  signal,  or  more  properly,  a Nyquist SOUND type. The function
snd-slider, described in Section 5.6.1, takes a slider  number  and  returns  a
SOUND  type  representing  the current value of the slider. To fully understand
this function, you need  to  know  something  about  how  Nyquist  is  actually
computing sounds.

  Sounds  are normally computed on demand. So the result returned by snd-slider
does not immediately compute  any  samples.  Samples  are  only  computed  when
something  tries  to  use  this signal. At that time, the slider value is read.
Normally, if the slider is used to control a sound, you will  hear  changes  in
the  sound  pretty soon after the slider value changes. However, one thing that
can interfere with this is that SOUND samples are computed in blocks  of  about
1000  samples.  When the slider value is read, the same value is used to fill a
block of 1000 samples, so even if the sample rate is 44,100 Hz,  the  effective
slider  sample  rate  is 44,100/1000, or 44.1 Hz. If you give the slider a very
low sample rate, say 1000, then slider value changes will only  be  noticed  by
Nyquist approximately once per second. For this reason, you should normally use
the audio sample rate (typically 44,100 Hz) for  the  rate  of  the  snd-slider
output  SOUND.  (Yes,  this is terribly wasteful to represent each slider value
with 1000 samples, but Nyquist was not designed  for  low-latency  computation,
and this is an expedient work-around.)

  In  addition  to  reading sliders as continually changing SOUNDs, you can get
the  slider  value  as  a  Lisp  FLONUM  (a  floating   point   number)   using
get-slider-value,  described  in Section 5.6.1. This might be useful if you are
computing a sequence of many notes (or other sound events) and  want  to  apply
the current slider value to the whole note or sound event.

  Note  that  if  you store the value returned by snd-slider in a variable, you
will capture the history of the slider changes. This will take a lot of memory,
so be careful.

  Suppose you write a simple expression such as (hzosc (mult 1000 (snd-slider 0
...))) to control an oscillator frequency with a slider.  How  long  does  this
sound  last? The duration of hzosc is the duration of the frequency control, so
what is the duration of a slider? To avoid infinitely long  signals,  you  must
specify a duration as one of the parameters of snd-slider.

  You  might  be thinking, what if I just want to tell the slider when to stop?
At present, you cannot do that, but in the future there should  be  a  function
that stops when its input goes to zero. Then, moving a slider to zero could end
the signal (and if you multiplied a  complex  sound  by  one  of  these  ending
functions, everything in the sound would end and be garbage collected).

  Another  thing  you  might  want to do with interactive control is start some
sound. The trigger function computes an instance of a  behavior  each  time  an
input  SOUND  goes  from  zero  to  greater-than-zero.  This could be used, for
example, to create a sequence of notes.

  The snd-slider function has some  parameters  that  may  be  unfamiliar.  The
second  parameter,  t0, is the starting time of the sound. This should normally
be (local-to-global 0), an expression that computes the instantiation  time  of
the  current  expression.  This  will often be zero, but if you call snd-slider
from inside a seq or seq-rep, the starting time may not be zero.

  The srate parameter is the sample rate to return. This should normally be the
audio  sample  rate  you  are  working with, which is typically *default-sound-
srate*.

II.1. Sending Open Sound Control Messages
  A variety of programs support  OSC.  The  only  OSC  message  interpreted  by
Nyquist has an address of /slider, and two parameters: an integer slider number
and a float value, nominally from 0.0 to 1.0.

  Two small programs are included in the Nyquist distribution for  sending  OSC
messages.  (Both can be found in the same directory as the nyquist executable.)
The first one, osc-test-client sends a sequence of  messages  that  just  cause
slider 0 to ramp slowly up and down. If you run this on a command line, you can
use "?" or "h" to get help information. There is an interactive mode that  lets
you send each OSC message by typing RETURN.

II.2. The ser-to-osc Program
  The  second  program  is  ser-to-osc,  a program that reads serial input (for
example from a PIC-based microcontroller) and  sends  OSC  messages.  Run  this
command-line  program  from a shell (a terminal window under OS X or Linux; use
the CMD program under Windows). You must name the serial input  device  on  the
command line, e.g. under OS X, you might run:

    ./ser-to-osc /dev/tty.usbserial-0000103D

(Note  that the program name is preceded by ``./". This tells the shell exactly
where to find the executable program in case the current directory  is  not  on
the search path for executable programs.)  Under Windows, you might run:

    ser-to-osc com4

(Note that you do not type ``./'' in front of a windows program.)

  To  use ser-to-osc, you will have to find the serial device. On the Macintosh
and Linux, try the following:

    ls /dev/*usb*

This will list all serial devices with ``usb'' in their  names.  Probably,  one
will  be  a name similar to /dev/tty.usbserial-0000103D. The ser-to-osc program
will echo data that it receives, so you  should  know  if  things  are  working
correctly.

  Under  Windows,  open  Control Panel from the Start menu, and open the System
control panel. Select the Hardware tab and click  the  Device  Manager  button.
Look  in  the device list under Ports (COM & LPT). When you plug in your serial
or USB device, you should see a new entry appear, e.g. COM4. This is the device
name you need.

  The format for the serial input is: any non-whitespace character(s), a slider
number, a slider value, and a newline (control-j or ASCII 0x0A).  These  fields
need  to be separated by tabs or spaces. An optional carriage return (control-m
or ASCII 0x0D) preceding the ASCII 0x0A is ignored. The slider number should be
in  decimal,  and  theh slider value is a decimal number from 0 to 255. This is
scaled to the range 0.0 to 1.0 (so an input of 255 translates to 1.0).

  There is a simple test program in demos/osc-test.lsp you can run to  try  out
control  with Open Sound Control. There are two examples in that file. One uses
snd-slider  to  control  the  frequency  of  an  oscillator.  The  other   uses
get-slider-value  to  control  the  pitch  of  grains  in  a granular synthesis
process.
III. Intgen
  This documentation describes Intgen, a program  for  generating  XLISP  to  C
interfaces.    Intgen works by scanning .h files with special comments in them.
Intgen builds stubs that implement XLISP SUBR's.   When  the  SUBR  is  called,
arguments are type-checked and passed to the C routine declared in the .h file.
Results are converted into the appropriate  XLISP  type  and  returned  to  the
calling  XLISP  function.    Intgen  lets  you  add  C functions into the XLISP
environment with very little effort.

  The interface generator will take as command-line input:

   - the name of the .c file to generate (do not include the .c extension;
     e.g. write xlexten, not xlexten.c);

   - a list of .h files.

Alternatively,  the  command line may specify a command file from which to read
file names. The command file name should be preceded by "@", for example:

    intgen @sndfns.cl

reads sndfns.cl to get the command-line input.  Only one level  of  indirection
is allowed.

  The output is:

   - a single .c file with one SUBR defined for each designated routine in
     a .h file.

   - a .h file that declares each new C routine.  E.g. if the .c  file  is
     named xlexten.c, this file will be named xlextendefs.h;

   - a  .h file that extends the SUBR table used by Xlisp.  E.g. if the .c
     file is named xlexten.c, then this file is named xlextenptrs.h;

   - a .lsp file with lisp initialization expressions copied from  the  .h
     files.    This  file is only generated if at least one initialization
     expression is encountered.

  For example, the command line

    intgen seint ~setypes.h access.h

generates the file seint.c,  using  declarations  in  setypes.h  and  access.h.
Normally,  the  .h  files  are  included  by  the generated file using #include
commands.  A ~ before a file means do not include the .h file.   (This  may  be
useful  if  you extend xlisp.h, which will be included anyway).  Also generated
will be setintdefs.h and seintptrs.h.



III.0.1. Extending Xlisp
  Any number of .h files may be named on the command line to Intgen, and Intgen
will make a single .c file with interface routines for all of the .h files.  On
the other hand, it is not necessary to put all of the extensions to Xlisp  into
a  single  interface  file.    For  example,  you  can run Intgen once to build
interfaces to window manager routines, and again to build interfaces to  a  new
data type.  Both interfaces can be linked into Xlisp.

  To  use the generated files, you must compile the .c files and link them with
all of the standard Xlisp object files.  In addition, you must  edit  the  file
localdefs.h  to  contain  an  #include for each *defs.h file, and edit the file
localptrs.h to include each *ptrs.h file.  For example, suppose you run  Intgen
to  build  soundint.c,  fugueint.c,  and  tableint.c.    You  would  then  edit
localdefs.h to contain the following:

    #include "soundintdefs.h"
    #include "fugueintdefs.h"
    #include "tableintdefs.h"

and edit localptrs.h to contain:

    #include "soundintptrs.h"
    #include "fugueintptrs.h"
    #include "tableintptrs.h"

These localdefs.h and localptrs.h files are in turn included by xlftab.c  which
is where Xlisp builds a table of SUBRs.

  To summarize, building an interface requires just a few simple steps:

   - Write  C  code to be called by Xlisp interface routines.  This C code
     does the real work, and in most cases is  completely  independent  of
     Xlisp.

   - Add  comments  to  .h  files  to  tell Intgen which routines to build
     interfaces to, and to specify the types of the arguments.

   - Run Intgen to build interface routines.

   - Edit localptrs.h and localdefs.h to include generated .h files.

   - Compile and link Xlisp, including the new C code.

III.1. Header file format
  Each routine to be interfaced with Xlisp must be declared as follows:

    type-name routine-name(); /* LISP: (func-name type  type  ...) */
                                                      1     2
The comment may be on the line following the declaration, but  the  declaration
and the comment must each be on no more than one line.  The characters LISP: at
the beginning of the comment mark routines  to  put  in  the  interface.    The
comment  also  gives  the  type  and  number  of arguments.  The function, when
accessed from lisp will  be  known  as  func-name,  which  need  not  bear  any
relationship to routine-name.  By convention, underscores in the C routine-name
should be converted to dashes in func-name, and  func-name  should  be  in  all
capitals.  None of this is enforced or automated though.

  Legal type_names are:

LVAL            returns an Xlisp datum.

atom_type       equivalent to LVAL, but the result is expected to be an atom.

value_type      a value as used in Dannenberg's score editor.

event_type      an event as used in Dannenberg's score editor.

int             interface will convert int to Xlisp FIXNUM.

boolean         interface will convert int to  T or nil.

float or double interface converts to FLONUM.

char * or string or string_type
                interface converts to STRING.  The result string will be copied
                into the XLISP heap.

void            interface will return nil.

  It  is easy to extend this list.  Any unrecognized type will be coerced to an
int and then returned as a FIXNUM, and a warning will be issued.

  The ``*'' after char must be followed by  routine-name  with  no  intervening
space.

  Parameter types may be any of the following:

FIXNUM          C routine expects an int.

FLONUM or FLOAT C routine expects a double.

STRING          C routine expects char *, the string is not copied.

VALUE           C routine expects a value_type.  (Not applicable to Fugue.)

EVENT           C routine expects an event_type.  (Not applicable to Fugue.)

ANY             C routine expects LVAL.

ATOM            C routine expects LVAL which is a lisp atom.

FILE            C routine expects FILE *.

SOUND           C routine expects a SoundPtr.

  Any  of  these  may  be  followed  by ``*'': FIXNUM*, FLONUM*, STRING*, ANY*,
FILE*, indicating C routine expects int *, double *, char **, LVAL *,  or  FILE
**  .    This is basically a mechanism for returning more than one value, not a
mechanism for clobbering XLisp values.  In this spirit,  the  interface  copies
the  value  (an  int,  double, char *, LVAL, or FILE *) to a local variable and
passes the address of that variable to the C routine.  On  return,  a  list  of
resulting  ``*'' parameters is constructed and bound to the global XLisp symbol
*RSLT*.  (Strings are copied.)  If the C routine is void, then the result  list
is also returned by the corresponding XLisp function.

  Note  1:  this  does  not support C routines like strcpy that modify strings,
because the C routine gets a pointer to the string in the XLisp heap.  However,
you  can always add an intermediate routine that allocates space and then calls
strcpy, or whatever.

  Note 2: it follows that a new XLisp STRING will be created for  each  STRING*
parameter.

  Note  3:  putting results on a (global!) symbol seems a bit unstructured, but
note that one could write  a  multiple-value  binding  macro  that  hides  this
ugliness  from the user if desired.  In practice, I find that pulling the extra
result values from *RSLT* when needed is perfectly acceptable.

  For parameters that are result  values  only,  the  character  ``^''  may  be
substituted  for ``*''.  In this case, the parameter is not to be passed in the
XLisp calling site.  However, the address of an initialized local  variable  of
the  given  type  is  passed to the corresponding C function, and the resulting
value is passed back through *RSLT* as ordinary result parameter  as  described
above.  The local variables are initialized to zero or NULL.

III.2. Using #define'd macros
  If a comment of the form:

    /* LISP: type-name (routine-name-2 type-1 type-2 ...) */

appears  on a line by itself and there was a #define on the previous line, then
the preceding #define is treated as a C routine, e.g.

    #define leftshift(val, count) ((val) << (count))
    /* LISP: int (LOGSHIFT INT INT) */

will implement the LeLisp function LOGSHIFT.

  The type-name following ``LISP:'' should have no spaces, e.g. use  ANY*,  not
ANY *.

III.3. Lisp Include Files
  Include files often define constants that we would like to have around in the
Lisp world, but which are easier to initialize just by  loading  a  text  file.
Therefore, a comment of the form:

    /* LISP-SRC: (any lisp expression) */

will cause Intgen to open a file name.lsp and append

    (any lisp expression)

to  name.lsp,  where name is the interface name passed on the command line.  If
none of the include files examined have comments of this form, then no name.lsp
file is generated.  Note: the LISP-SRC comment must be on a new line.

III.4. Example
  This  file was used for testing Intgen.  It uses a trick (ok, it's a hack) to
interface to a standard library macro (tolower).    Since  tolower  is  already
defined,  the macro ToLower is defined just to give Intgen a name to call.  Two
other routines, strlen and tough, are interfaced as well.

    /* igtest.h -- test interface for intgen */

    #define ToLower(c) tolower(c)
    /* LISP: int (TOLOWER FIXNUM) */

    int strlen();   /* LISP: (STRLEN STRING) */

    void tough();
      /* LISP: (TOUGH FIXNUM* FLONUM* STRING ANY FIXNUM) */

III.5. More Details
  Intgen has some compiler switches to enable/disable the use of certain types,
including  VALUE  and  EVENT types used by Dannenberg's score editing work, the
SOUND type used by Fugue,  and  DEXT  and  SEXT  types  added  for  Dale  Amon.
Enabling  all  of  these is not likely to cause problems, and the chances of an
accidental use of these types getting through the  compiler  and  linker  seems
very small.
IV. XLISP: An Object-oriented Lisp

                                  Version 2.0

                               February 6, 1988

                                      by
                              David Michael Betz
                                127 Taylor Road
                            Peterborough, NH 03458

                   Copyright (c) 1988, by David Michael Betz
                              All Rights Reserved
           Permission is granted for unrestricted non-commercial use
IV.1. Introduction
  XLISP  is an experimental programming language combining some of the features
of  Common  Lisp  with  an  object-oriented  extension  capability.    It   was
implemented  to allow experimentation with object-oriented programming on small
computers.

  Implementations of XLISP run on virtually every operating system.   XLISP  is
completely  written  in  the programming language C and is easily extended with
user written built-in functions and classes.  It is available in source form to
non-commercial users.

  Many  Common Lisp functions are built into XLISP.  In addition, XLISP defines
the objects Object and Class as primitives.  Object is the only class that  has
no  superclass and hence is the root of the class hierarchy tree.  Class is the
class of which all classes are instances (it is the  only  object  that  is  an
instance of itself).

  This  document is a brief description of XLISP.  It assumes some knowledge of
LISP and some understanding of the concepts of object-oriented programming.

  I recommend the book Lisp by Winston and Horn and published by Addison Wesley
for  learning Lisp.  The first edition of this book is based on MacLisp and the
second edition is based on Common Lisp.

  You will probably also need a copy  of  Common  Lisp:  The  Language  by  Guy
L.  Steele,  Jr.,  published by Digital Press to use as a reference for some of
the Common Lisp functions that are described only briefly in this document.

IV.2. A Note From The Author
  If you have any problems with XLISP, feel free to contact me [me being  David
Betz  - RBD] for help or advice.  Please remember that since XLISP is available
in source form in a high level  language,  many  users  [e.g.  that  Dannenberg
fellow - RBD] have been making versions available on a variety of machines.  If
you call to report a problem with a specific version, I may not be able to help
you  if  that  version  runs on a machine to which I don't have access.  Please
have the version number of the version that you are running readily  accessible
before calling me.

  If  you  find  a  bug  in  XLISP, first try to fix the bug yourself using the
source code provided.  If you are successful in fixing the bug,  send  the  bug
report  along  with the fix to me.  If you don't have access to a C compiler or
are unable to fix a bug, please send the bug report to me and I'll try  to  fix
it.

  Any  suggestions  for improvements will be welcomed.  Feel free to extend the
language in whatever way suits your needs.   However,  PLEASE  DO  NOT  RELEASE
ENHANCED  VERSIONS  WITHOUT  CHECKING  WITH  ME FIRST!!  I would like to be the
clearing house for new features added to XLISP.  If you want  to  add  features
for  your  own  personal  use,  go  ahead.  But, if you want to distribute your
enhanced version, contact me first.  Please remember that the goal of XLISP  is
to  provide  a  language  to learn and experiment with LISP and object-oriented
programming on small computers.  I don't want it to get so big that it requires
megabytes of memory to run.

IV.3. XLISP Command Loop
  When  XLISP  is  started, it first tries to load the workspace xlisp.wks from
the current directory.  If that file doesn't exist,  XLISP  builds  an  initial
workspace, empty except for the built-in functions and symbols.

  Then  XLISP  attempts  to  load init.lsp from the current directory.  It then
loads any files named as parameters on the command line (after  appending  .lsp
to their names).

  XLISP then issues the following prompt:

            >

This indicates that XLISP is waiting for an expression to be typed.

  When  a complete expression has been entered, XLISP attempts to evaluate that
expression.  If the expression evaluates successfully, XLISP prints the  result
and  then  returns  to  the initial prompt waiting for another expression to be
typed.

IV.4. Special Characters
  When XLISP  is  running  from  a  console,  some  control  characters  invoke
operations:

   - Backspace  and  Delete characters erase the previous character on the
     input line (if any).

   - Control-U erases the entire input line.

   - Control-C executes the TOP-LEVEL function.

   - Control-G executes the CLEAN-UP function.

   - Control-P executes the CONTINUE function.

   - Control-B  stops  execution  and  enters  the  break  command   loop.
     Execution can be continued by typing Control-P or (CONTINUE).

   - Control-E turns on character echoing (Linux and Mac OS X only).

   - Control-F turns off character echoing (Linux and Mac OS X only).

   - Control-T evaluates the INFO function.

IV.5. Break Command Loop
  When XLISP encounters an error while evaluating an expression, it attempts to
handle the error in the following way:

  If the symbol *breakenable* is true, the message corresponding to  the  error
is printed.  If the error is correctable, the correction message is printed.

  If  the  symbol *tracenable* is true, a trace back is printed.  The number of
entries printed depends on the value of  the  symbol  *tracelimit*.    If  this
symbol  is set to something other than a number, the entire trace back stack is
printed.

  XLISP then enters a read/eval/print loop to allow the  user  to  examine  the
state  of  the interpreter in the context of the error.  This loop differs from
the normal top-level read/eval/print loop in  that  if  the  user  invokes  the
function  continue,  XLISP will continue from a correctable error.  If the user
invokes the function clean-up, XLISP will abort the break loop  and  return  to
the  top  level  or  the next lower numbered break loop.  When in a break loop,
XLISP prefixes the break level to the normal prompt.

  If the symbol *breakenable* is nil, XLISP  looks  for  a  surrounding  errset
function.    If  one  is found, XLISP examines the value of the print flag.  If
this flag is true, the error message is printed.  In any case, XLISP causes the
errset function call to return nil.

  If  there  is  no surrounding errset function, XLISP prints the error message
and returns to the top level.

IV.6. Data Types
  There are several different data types available to XLISP programmers.

   - lists

   - symbols

   - strings

   - integers

   - characters

   - floats

   - objects

   - arrays

   - streams

   - subrs (built-in functions)

   - fsubrs (special forms)

   - closures (user defined functions)

IV.7. The Evaluator
  The process of evaluation in XLISP:

   - Strings, integers,  characters,  floats,  objects,  arrays,  streams,
     subrs, fsubrs and closures evaluate to themselves.

   - Symbols  act  as  variables and are evaluated by retrieving the value
     associated with their current binding.

   - Lists are evaluated by examining the first element of  the  list  and
     then taking one of the following actions:

        * If  it  is  a  symbol,  the  functional binding of the symbol is
          retrieved.

        * If it is a lambda expression, a closure is constructed  for  the
          function described by the lambda expression.

        * If it is a subr, fsubr or closure, it stands for itself.

        * Any other value is an error.

     Then, the value produced by the previous step is examined:

        * If  it  is  a  subr  or closure, the remaining list elements are
          evaluated and the subr or closure is called with these evaluated
          expressions as arguments.

        * If  it is an fsubr, the fsubr is called using the remaining list
          elements as arguments (unevaluated).

        * If it is a macro, the macro is expanded using the remaining list
          elements  as  arguments  (unevaluated).   The macro expansion is
          then evaluated in place of the original macro call.

IV.8. Lexical Conventions
  The following conventions must be followed when entering XLISP programs:

  Comments in XLISP code begin with a semi-colon character and continue to  the
end of the line.

  Symbol  names  in  XLISP  can  consist of any sequence of non-blank printable
characters except the following:

                    ( ) ' ` , " ;

Uppercase and lowercase characters are not distinguished within  symbol  names.
All lowercase characters are mapped to uppercase on input.

  Integer  literals consist of a sequence of digits optionally beginning with a
+ or -.  The range of values an integer can represent is limited by the size of
a C long on the machine on which XLISP is running.

  Floating  point literals consist of a sequence of digits optionally beginning
with a + or - and including an embedded decimal point.  The range of  values  a
floating point number can represent is limited by the size of a C float (double
on machines with 32 bit addresses) on the machine on which XLISP is running.

  Literal strings are sequences of  characters  surrounded  by  double  quotes.
Within  quoted  strings  the  ``\''  character  is  used to allow non-printable
characters to be included.  The codes recognized are:

   - \\ means the character ``\''

   - \n means newline

   - \t means tab

   - \r means return

   - \f means form feed

   - \nnn means the character whose octal code is nnn

IV.9. Readtables
  The behavior of the reader  is  controlled  by  a  data  structure  called  a
readtable.    The  reader  uses  the  symbol  *readtable* to locate the current
readtable.  This table controls the interpretation of input characters.  It  is
an  array  with  128  entries, one for each of the ASCII character codes.  Each
entry contains one of the following things:

   - NIL M Indicating an invalid character

   - :CONSTITUENT M Indicating a symbol constituent

   - :WHITE-SPACE M Indicating a whitespace character

   - (:TMACRO . fun) M Terminating readmacro

   - (:NMACRO . fun) M Non-terminating readmacro

   - :SESCAPE M Single escape character ('\')

   - :MESCAPE M Multiple escape character ('|')

  In the case of :TMACRO and :NMACRO, the fun component is a  function.    This
can  either  be  a  built-in  readmacro  function  or a lambda expression.  The
function should take two parameters.  The first is the  input  stream  and  the
second  is  the  character  that  caused  the invocation of the readmacro.  The
readmacro function should return NIL to indicate that the character  should  be
treated  as  white  space  or  a  value  consed  with  NIL to indicate that the
readmacro should be treated as an occurence of the specified value.  Of course,
the readmacro code is free to read additional characters from the input stream.

  XLISP defines several useful read macros:

   - '<expr> == (quote <expr>)

   - #'<expr> == (function <expr>)

   - #(<expr>...)  == an array of the specified expressions

   - #x<hdigits> == a hexadecimal number (0-9,A-F)

   - #o<odigits> == an octal number (0-7)

   - #b<bdigits> == a binary number (0-1)

   - #\<char> == the ASCII code of the character

   - #| ... |# == a comment

   - #:<symbol> == an uninterned symbol

   - `<expr> == (backquote <expr>)

   - ,<expr> == (comma <expr>)

   - ,@<expr> == (comma-at <expr>)

IV.10. Lambda Lists
  There  are  several  forms  in  XLISP  that require that a ``lambda list'' be
specified.  A lambda list is a  definition  of  the  arguments  accepted  by  a
function.  There are four different types of arguments.

  The  lambda  list starts with required arguments.  Required arguments must be
specified in every call to the function.

  The required arguments are followed by the  &optional  arguments.    Optional
arguments  may  be provided or omitted in a call.  An initialization expression
may be specified to provide a default value for an &optional argument if it  is
omitted  from a call.  If no initialization expression is specified, an omitted
argument is initialized to NIL.  It is also possible to provide the name  of  a
supplied-p  variable  that  can be used to determine if a call provided a value
for the argument or if the initialization expression was used.   If  specified,
the  supplied-  p  variable  will be bound to T if a value was specified in the
call and NIL if the default value was used.

  The &optional arguments are followed  by  the  &rest  argument.    The  &rest
argument  gets  bound  to the remainder of the argument list after the required
and &optional arguments have been removed.

  The &rest argument is followed  by  the  &key  arguments.    When  a  keyword
argument  is  passed  to  a  function, a pair of values appears in the argument
list.  The first expression in the pair should evaluate to a keyword symbol  (a
symbol  that  begins  with a ``:'').  The value of the second expression is the
value of the keyword argument.  Like &optional arguments,  &key  arguments  can
have  initialization  expressions and supplied-p variables.  In addition, it is
possible to specify the keyword to be used in a function call.  If  no  keyword
is  specified,  the  keyword obtained by adding a ``:'' to the beginning of the
keyword argument symbol is used.  In  other  words,  if  the  keyword  argument
symbol is foo, the keyword will be ':foo.

  The  &key  arguments  are  followed  by  the &aux variables.  These are local
variables that are bound during the evaluation of the function  body.    It  is
possible to have initialization expressions for the &aux variables.

  Here is the complete syntax for lambda lists:

                    (rarg...
                     [&optional [oarg | (oarg [init [svar]])]...]
                     [&rest rarg]
                     [&key
                       [karg | ([karg | (key karg)] [init [svar]])]...
                       &allow-other-keys]
                     [&aux
                       [aux | (aux [init])]...])

                where:

                    rarg is a required argument symbol
                    oarg is an &optional argument symbol
                    rarg is the &rest argument symbol
                    karg is a &key argument symbol
                    key is a keyword symbol
                    aux is an auxiliary variable symbol
                    init is an initialization expression
                    svar is a supplied-p variable symbol

IV.11. Objects
  Definitions:

   - selector M a symbol used to select an appropriate method

   - message M a selector and a list of actual arguments

   - method M the code that implements a message

Since  XLISP  was  created  to  provide  a  simple basis for experimenting with
object-oriented programming, one  of  the  primitive  data  types  included  is
object.   In XLISP, an object consists of a data structure containing a pointer
to the object's class as well as an array containing the values of the object's
instance variables.

  Officially,  there  is  no way to see inside an object (look at the values of
its instance variables).  The only way to communicate  with  an  object  is  by
sending it a message.

  You  can  send a message to an object using the send function.  This function
takes the object as its first argument, the  message  selector  as  its  second
argument  (which  must  be a symbol) and the message arguments as its remaining
arguments.

  The send function determines the class of the receiving object  and  attempts
to  find  a method corresponding to the message selector in the set of messages
defined for that class.  If the message is not found in the object's class  and
the  class  has  a super-class, the search continues by looking at the messages
defined for the super-class.  This process continues from  one  super-class  to
the  next  until  a method for the message is found.  If no method is found, an
error occurs.

  When a method is found, the evaluator  binds  the  receiving  object  to  the
symbol  self  and  evaluates  the  method  using  the remaining elements of the
original list as arguments to the method.  These arguments are always evaluated
prior  to  being  bound to their corresponding formal arguments.  The result of
evaluating the method becomes the result of the expression.

  Within the body of a method, a message can be sent to the current  object  by
calling  the  (send self ...). The method lookup starts with the object's class
regardless of the class containing the current method.

  Sometimes it is desirable to invoke a general method  in  a  superclass  even
when  it  is  overridden  by a more specific method in a subclass.  This can be
accomplished by calling send-super, which  begins  the  method  lookup  in  the
superclass of the class defining the current method rather than in the class of
the current object.

  The send-super function takes a selector as its first argument (which must be
a  symbol)  and  the  message arguments as its remaining arguments. Notice that
send-super can only be sent from within a method, and the target of the message
is  always the current object (self). (send-super ...) is similar to (send self
...) except that method lookup begins in the superclass of the class containing
the current method rather than the class of the current object.
IV.12. The ``Object'' Class
  Object M the top of the class hierarchy.

  Messages:
:show M show an object's instance variables.
     returns M the object

:class M return the class of an object
     returns M the class of the object

:isa(:isa) class M test if object inherits from class
     returns  M  t  if  object  is an instance of class or a subclass of class,
          otherwise nil

:isnew M the default object initialization routine
     returns M the object

IV.13. The ``Class'' Class
  Class M class of all object classes (including itself)

  Messages:
:new M create a new instance of a class
     returns M the new class object

:isnew ivars [cvars [super]] M initialize a new class
     ivars M the list of instance variable symbols
     cvars M the list of class variable symbols
     super M the superclass (default is object)
     returns M the new class object

:answer msg fargs code M add a message to a class
     msg M the message symbol
     fargs M the formal argument list (lambda list)
     code M a list of executable expressions
     returns M the object

  When a new instance of a class is created by sending the message :new  to  an
existing  class, the message :isnew followed by whatever parameters were passed
to the :new message is sent to the newly created object.

  When a new class is created by sending the :new message to the object  Class,
an  optional  parameter  may  be specified indicating the superclass of the new
class.  If this parameter is omitted, the new  class  will  be  a  subclass  of
Object.   A class inherits all instance variables, class variables, and methods
from its super-class.

IV.14. Profiling
  The Xlisp 2.0 release has been extended  with  a  profiling  facility,  which
counts  how  many  times  and  where  eval  is  executed.   A separate count is
maintained for each named function, closure, or macro, and a count indicates an
eval  in  the  immediately  (lexically)  enclosing  named function, closure, or
macro.  Thus, the count gives an indication of the amount of time  spent  in  a
function,  not  counting  nested  function  calls.    The list of all functions
executed is maintained on the global *profile* variable.   These  functions  in
turn  have *profile* properties, which maintain the counts.  The profile system
merely increments counters and puts symbols on the *profile* list.  It is up to
the  user to initialize data and gather results.  Profiling is turned on or off
with the profile function.  Unfortunately, methods cannot be profiled with this
facility.

IV.15. Symbols

   - self M the current object (within a method context)

   - *obarray* M the object hash table

   - *standard-input* M the standard input stream

   - *standard-output* M the standard output stream

   - *error-output* M the error output stream

   - *trace-output* M the trace output stream

   - *debug-io* M the debug i/o stream

   - *breakenable* M flag controlling entering break loop on errors

   - *tracelist* M list of names of functions to trace

   - *tracenable* M enable trace back printout on errors

   - *tracelimit* M number of levels of trace back information

   - *evalhook* M user substitute for the evaluator function

   - *applyhook* M (not yet implemented)

   - *readtable* M the current readtable

   - *unbound* M indicator for unbound symbols

   - *gc-flag* M controls the printing of gc messages

   - *gc-hook* M function to call after garbage collection

   - *integer-format* M format for printing integers (``%d'' or ``%ld'')

   - *float-format* M format for printing floats (``%g'')

   - *print-case* M symbol output case (:upcase or :downcase)

  There  are  several  symbols  maintained  by  the  read/eval/print loop.  The
symbols +, ++, and +++ are bound to the most recent  three  input  expressions.
The  symbols  *,  **  and  *** are bound to the most recent three results.  The
symbol - is bound to the expression currently being evaluated.  It becomes  the
value of + at the end of the evaluation.

IV.16. Evaluation Functions
(eval expr) M evaluate an xlisp expression
     expr M the expression to be evaluated
     returns M the result of evaluating the expression

(apply fun args) M apply a function to a list of arguments
     fun M the function to apply (or function symbol)
     args M the argument list
     returns M the result of applying the function to the arguments

(funcall fun arg...) M call a function with arguments
     fun M the function to call (or function symbol)
     arg M arguments to pass to the function
     returns M the result of calling the function with the arguments

(quote expr) M return an expression unevaluated
     expr M the expression to be quoted (quoted)
     returns M expr unevaluated

(function expr) M get the functional interpretation
     expr M the symbol or lambda expression (quoted)
     returns M the functional interpretation

(backquote expr) M fill in a template
     expr M the template
     returns M a copy of the template with comma and comma-at
     expressions expanded

(lambda args expr...) M make a function closure
     args M formal argument list (lambda list) (quoted)
     expr M expressions of the function body
     returns M the function closure

(get-lambda-expression closure) M get the lambda expression
     closure M the closure
     returns M the original lambda expression

(macroexpand form) M recursively expand macro calls
     form M the form to expand
     returns M the macro expansion

(macroexpand-1 form) M expand a macro call
     form M the macro call form
     returns M the macro expansion


IV.17. Symbol Functions
(set sym expr) M set the value of a symbol
     sym M the symbol being set
     expr M the new value
     returns M the new value

(setq [sym expr]...) M set the value of a symbol
     sym M the symbol being set (quoted)
     expr M the new value
     returns M the new value

(psetq [sym expr]...)  M parallel version of setq
     sym M the symbol being set (quoted)
     expr M the new value
     returns M the new value

(setf [place expr]...)  M set the value of a field
     place M the field specifier (quoted):
          sym M set value of a symbol
          (car expr) M set car of a cons node
          (cdr expr) M set cdr of a cons node
          (nth n expr) M set nth car of a list
          (aref expr n) M set nth element of an array
          (get sym prop) M set value of a property
          (symbol-value sym) M set value of a symbol
          (symbol-function sym) M set functional value of a symbol
          (symbol-plist sym) M set property list of a symbol
     expr M the new value
     returns M the new value

(defun  sym  fargs expr...)  M define a function (defmacro sym fargs expr...) M
     define a macro
     sym M symbol being defined (quoted)
     fargs M formal argument list (lambda list) (quoted)
     expr M expressions constituting the body of the
     function (quoted) returns M the function symbol

(gensym [tag]) M generate a symbol
     tag M string or number
     returns M the new symbol

(intern pname) M make an interned symbol
     pname M the symbol's print name string
     returns M the new symbol

(make-symbol pname) M make an uninterned symbol
     pname M the symbol's print name string
     returns M the new symbol

(symbol-name sym) M get the print name of a symbol
     sym M the symbol
     returns M the symbol's print name

(symbol-value sym) M get the value of a symbol
     sym M the symbol
     returns M the symbol's value

(symbol-function sym) M get the functional value of a symbol
     sym M the symbol
     returns M the symbol's functional value

(symbol-plist sym) M get the property list of a symbol
     sym M the symbol
     returns M the symbol's property list

(hash sym n) M compute the hash index for a symbol
     sym M the symbol or string
     n M the table size (integer)
     returns M the hash index (integer)


IV.18. Property List Functions
(get sym prop) M get the value of a property
     sym M the symbol
     prop M the property symbol
     returns M the property value or nil

(putprop sym val prop) M put a property onto a property list
     sym M the symbol
     val M the property value
     prop M the property symbol
     returns M the property value

(remprop sym prop) M remove a property
     sym M the symbol
     prop M the property symbol
     returns M nil


IV.19. Array Functions
(aref array n) M get the nth element of an array
     array M the array
     n M the array index (integer)
     returns M the value of the array element

(make-array size) M make a new array
     size M the size of the new array (integer)
     returns M the new array

(vector expr...)  M make an initialized vector
     expr M the vector elements
     returns M the new vector


IV.20. List Functions
(car expr) M return the car of a list node
     expr M the list node
     returns M the car of the list node

(cdr expr) M return the cdr of a list node
     expr M the list node
     returns M the cdr of the list node

(cxxr expr) M all cxxr combinations

(cxxxr expr) M all cxxxr combinations

(cxxxxr expr) M all cxxxxr combinations

(first expr) M a synonym for car

(second expr) M a synonym for cadr

(third expr) M a synonym for caddr

(fourth expr) M a synonym for cadddr

(rest expr) M a synonym for cdr

(cons expr1 expr2) M construct a new list node
     expr1 M the car of the new list node
     expr2 M the cdr of the new list node
     returns M the new list node

(list expr...)  M create a list of values
     expr M expressions to be combined into a list
     returns M the new list

(append expr...)  M append lists
     expr M lists whose elements are to be appended
     returns M the new list

(reverse expr) M reverse a list
     expr M the list to reverse
     returns M a new list in the reverse order

(last list) M return the last list node of a list
     list M the list
     returns M the last list node in the list

(member expr list &key :test :test-not) M find an expression in a list
     expr M the expression to find
     list M the list to search
     :test M the test function (defaults to eql)
     :test-not M the test function (sense inverted)
     returns M the remainder of the list starting with the expression

(assoc expr alist &key :test :test-not) M find an expression in an a-list
     expr M the expression to find
     alist M the association list
     :test M the test function (defaults to eql)
     :test-not M the test function (sense inverted)
     returns M the alist entry or nil

(remove expr list &key :test :test-not) M remove elements from a list
     expr M the element to remove
     list M the list
     :test M the test function (defaults to eql)
     :test-not M the test function (sense inverted)
     returns M copy of list with matching expressions removed

(remove-if test list) M remove elements that pass test
     test M the test predicate
     list M the list
     returns M copy of list with matching elements removed

(remove-if-not test list) M remove elements that fail test
     test M the test predicate
     list M the list
     returns M copy of list with non-matching elements removed

(length expr) M find the length of a list, vector or string
     expr M the list, vector or string
     returns M the length of the list, vector or string

(nth n list) M return the nth element of a list
     n M the number of the element to return (zero origin)
     list M the list
     returns M the nth element or nil if the list isn't that long

(nthcdr n list) M return the nth cdr of a list
     n M the number of the element to return (zero origin)
     list M the list
     returns M the nth cdr or nil if the list isn't that long

(mapc fcn list1 list...)  M apply function to successive cars
     fcn M the function or function name
     listn M a list for each argument of the function
     returns M the first list of arguments

(mapcar fcn list1 list...)  M apply function to successive cars
     fcn M the function or function name
     listn M a list for each argument of the function
     returns M a list of the values returned

(mapl fcn list1 list...)  M apply function to successive cdrs
     fcn M the function or function name
     listn M a list for each argument of the function
     returns M the first list of arguments

(maplist fcn list1 list...)  M apply function to successive cdrs
     fcn M the function or function name
     listn M a list for each argument of the function
     returns M a list of the values returned

(subst to from expr &key :test :test-not) M substitute expressions
     to M the new expression
     from M the old expression
     expr M the expression in which to do the substitutions
     :test M the test function (defaults to eql)
     :test-not M the test function (sense inverted)
     returns M the expression with substitutions

(sublis alist expr &key :test :test-not) M substitute with an a-list
     alist M the association list
     expr M the expression in which to do the substitutions
     :test M the test function (defaults to eql)
     :test-not M the test function (sense inverted)
     returns M the expression with substitutions


IV.21. Destructive List Functions
(rplaca list expr) M replace the car of a list node
     list M the list node
     expr M the new value for the car of the list node
     returns M the list node after updating the car

(rplacd list expr) M replace the cdr of a list node
     list M the list node
     expr M the new value for the cdr of the list node
     returns M the list node after updating the cdr

(nconc list...)  M destructively concatenate lists
     list M lists to concatenate
     returns M the result of concatenating the lists
(delete expr &key :test :test-not) M delete elements from a list
     expr M the element to delete
     list M the list
     :test M the test function (defaults to eql)
     :test-not M the test function (sense inverted)
     returns M the list with the matching expressions deleted

(delete-if test list) M delete elements that pass test
     test M the test predicate
     list M the list
     returns M the list with matching elements deleted

(delete-if-not test list) M delete elements that fail test
     test M the test predicate
     list M the list
     returns M the list with non-matching elements deleted

(sort list test) M sort a list
     list M the list to sort
     test M the comparison function
     returns M the sorted list


IV.22. Predicate Functions
(atom expr) M is this an atom?
     expr M the expression to check
     returns M t if the value is an atom, nil otherwise

(symbolp expr) M is this a symbol?
     expr M the expression to check
     returns M t if the expression is a symbol, nil otherwise

(numberp expr) M is this a number?
     expr M the expression to check
     returns M t if the expression is a number, nil otherwise

(null expr) M is this an empty list?
     expr M the list to check
     returns M t if the list is empty, nil otherwise

(not expr) M is this false?
     expr M the expression to check
     return M t if the value is nil, nil otherwise

(listp expr) M is this a list?
     expr M the expression to check
     returns M t if the value is a cons or nil, nil otherwise

(endp list) M is this the end of a list
     list M the list
     returns M t if the value is nil, nil otherwise

(consp expr) M is this a non-empty list?
     expr M the expression to check
     returns M t if the value is a cons, nil otherwise

(integerp expr) M is this an integer?
     expr M the expression to check
     returns M t if the value is an integer, nil otherwise

(floatp expr) M is this a float?
     expr M the expression to check
     returns M t if the value is a float, nil otherwise

(stringp expr) M is this a string?
     expr M the expression to check
     returns M t if the value is a string, nil otherwise

(characterp expr) M is this a character?
     expr M the expression to check
     returns M t if the value is a character, nil otherwise

(arrayp expr) M is this an array?
     expr M the expression to check
     returns M t if the value is an array, nil otherwise

(streamp expr) M is this a stream?
     expr M the expression to check
     returns M t if the value is a stream, nil otherwise

(objectp expr) M is this an object?
     expr M the expression to check
     returns M t if the value is an object, nil otherwise

(filep expr)(This is not part of standard XLISP nor  is  it  built-in.  Nyquist
     defines it though.)  M is this a file?
     expr M the expression to check
     returns M t if the value is an object, nil otherwise

(boundp sym) M is a value bound to this symbol?
     sym M the symbol
     returns M t if a value is bound to the symbol, nil otherwise

(fboundp sym) M is a functional value bound to this symbol?
     sym M the symbol
     returns M t if a functional value is bound to the symbol,
     nil otherwise

(minusp expr) M is this number negative?
     expr M the number to test
     returns M t if the number is negative, nil otherwise

(zerop expr) M is this number zero?
     expr M the number to test
     returns M t if the number is zero, nil otherwise

(plusp expr) M is this number positive?
     expr M the number to test
     returns M t if the number is positive, nil otherwise

(evenp expr) M is this integer even?
     expr M the integer to test
     returns M t if the integer is even, nil otherwise

(oddp expr) M is this integer odd?
     expr M the integer to test
     returns M t if the integer is odd, nil otherwise

(eq expr1 expr2) M are the expressions identical?
     expr1 M the first expression
     expr2 M the second expression
     returns M t if they are equal, nil otherwise

(eql expr1 expr2) M are the expressions identical? (works with all numbers)
     expr1 M the first expression
     expr2 M the second expression
     returns M t if they are equal, nil otherwise

(equal expr1 expr2) M are the expressions equal?
     expr1 M the first expression
     expr2 M the second expression
     returns M t if they are equal, nil otherwise


IV.23. Control Constructs
(cond pair...)  M evaluate conditionally
     pair M pair consisting of:
          (pred expr...)
     where:
          pred M is a predicate expression
          expr M evaluated if the predicate is not nil
     returns M the value of the first expression whose predicate is not nil

(and expr...)  M the logical and of a list of expressions
     expr M the expressions to be anded
     returns  M  nil if any expression evaluates to nil, otherwise the value of
          the last expression (evaluation of expressions stops after the  first
          expression that evaluates to nil)

(or expr...)  M the logical or of a list of expressions
     expr M the expressions to be ored
     returns  M  nil if all expressions evaluate to nil, otherwise the value of
          the first non-nil expression (evaluation of expressions  stops  after
          the first expression that does not evaluate to nil)

(if texpr expr1 [expr2]) M evaluate expressions conditionally
     texpr M the test expression
     expr1 M the expression to be evaluated if texpr is non-nil
     expr2 M the expression to be evaluated if texpr is nil
     returns M the value of the selected expression

(when texpr expr...)  M evaluate only when a condition is true
     texpr M the test expression
     expr M the expression(s) to be evaluated if texpr is non-nil
     returns M the value of the last expression or nil

(unless texpr expr...)  M evaluate only when a condition is false
     texpr M the test expression
     expr M the expression(s) to be evaluated if texpr is nil
     returns M the value of the last expression or nil

(case expr case...)  M select by case
     expr M the selection expression
     case M pair consisting of:
          (value expr...)
     where:
          value M is a single expression or a list of expressions (unevaluated)
          expr M are expressions to execute if the case matches
     returns M the value of the last expression of the matching case

(let (binding...) expr...)  M create local bindings (let* (binding...) expr...)
     M let with sequential binding
     binding M the variable bindings each of which is either:
          1) a symbol (which is initialized to nil)
          2) a list whose car is a symbol and whose cadr is  an  initialization
               expression
     expr M the expressions to be evaluated
     returns M the value of the last expression

(flet  (binding...)  expr...)    M  create local functions (labels (binding...)
     expr...) M flet with recursive functions (macrolet (binding...) expr...) M
     create local macros
     binding M the function bindings each of which is:
          (sym fargs expr...)
     where:
          sym M the function/macro name
          fargs M formal argument list (lambda list)
          expr M expressions constituting the body of the function/macro
     expr M the expressions to be evaluated
     returns M the value of the last expression

(catch sym expr...)  M evaluate expressions and catch throws
     sym M the catch tag
     expr M expressions to evaluate
     returns M the value of the last expression the throw expression

(throw sym [expr]) M throw to a catch
     sym M the catch tag
     expr M the value for the catch to return (defaults to nil)
     returns M never returns

(unwind-protect expr cexpr...)  M protect evaluation of an expression
     expr M the expression to protect
     cexpr M the cleanup expressions
     returns M the value of the expression
     Note:    unwind-protect guarantees to execute the cleanup expressions even
          if a non-local  exit  terminates  the  evaluation  of  the  protected
          expression


IV.24. Looping Constructs
(loop expr...)  M basic looping form
     expr M the body of the loop
     returns M never returns (must use non-local exit)

(do  (binding...) (texpr rexpr...) expr...)  (do* (binding...) (texpr rexpr...)
     expr...)
     binding M the variable bindings each of which is either:
          1) a symbol (which is initialized to nil)
          2) a list of the form: (sym init [step]) where:
               sym M is the symbol to bind
               init M is the initial value of the symbol
               step M is a step expression
     texpr M the termination test expression
     rexpr M result expressions (the default is nil)
     expr M the body of the loop (treated like an implicit prog)
     returns M the value of the last result expression

(dolist (sym expr [rexpr]) expr...)  M loop through a list
     sym M the symbol to bind to each list element
     expr M the list expression
     rexpr M the result expression (the default is nil)
     expr M the body of the loop (treated like an implicit prog)

(dotimes (sym expr [rexpr]) expr...)  M loop from zero to n-1
     sym M the symbol to bind to each value from 0 to n-1
     expr M the number of times to loop
     rexpr M the result expression (the default is nil)
     expr M the body of the loop (treated like an implicit prog)


IV.25. The Program Feature
(prog (binding...) expr...)  M the program feature (prog* (binding...) expr...)
     M prog with sequential binding
     binding M the variable bindings each of which is either:
          1) a symbol (which is initialized to nil)
          2)  a  list whose car is a symbol and whose cadr is an initialization
               expression
     expr M expressions to evaluate or tags (symbols)
     returns M nil or the argument passed to the return function

(block name expr...)  M named block
     name M the block name (symbol)
     expr M the block body
     returns M the value of the last expression

(return [expr]) M cause a prog construct to return a value
     expr M the value (defaults to nil)
     returns M never returns

(return-from name [value]) M return from a named block
     name M the block name (symbol)
     value M the value to return (defaults to nil)
     returns M never returns

(tagbody expr...)  M block with labels
     expr M expression(s) to evaluate or tags (symbols)
     returns M nil

(go sym) M go to a tag within a tagbody or prog
     sym M the tag (quoted)
     returns M never returns

(progv slist vlist expr...)  M dynamically bind symbols
     slist M list of symbols
     vlist M list of values to bind to the symbols
     expr M expression(s) to evaluate
     returns M the value of the last expression

(prog1 expr1 expr...)  M execute expressions sequentially
     expr1 M the first expression to evaluate
     expr M the remaining expressions to evaluate
     returns M the value of the first expression

(prog2 expr1 expr2 expr...)  M execute expressions sequentially
     expr1 M the first expression to evaluate
     expr2 M the second expression to evaluate
     expr M the remaining expressions to evaluate
     returns M the value of the second expression

(progn expr...)  M execute expressions sequentially
     expr M the expressions to evaluate
     returns M the value of the last expression (or nil)


IV.26. Debugging and Error Handling
(trace sym) M add a function to the trace list
     sym M the function to add (quoted)
     returns M the trace list

(untrace sym) M remove a function from the trace list
     sym M the function to remove (quoted)
     returns M the trace list

(error emsg [arg]) M signal a non-correctable error
     emsg M the error message string
     arg M the argument expression (printed after the message)
     returns M never returns

(cerror cmsg emsg [arg]) M signal a correctable error
     cmsg M the continue message string
     emsg M the error message string
     arg M the argument expression (printed after the message)
     returns M nil when continued from the break loop

(break [bmsg [arg]]) M enter a break loop
     bmsg M the break message string (defaults to **break**)
     arg M the argument expression (printed after the message)
     returns M nil when continued from the break loop

(clean-up) M clean-up after an error
     returns M never returns

(top-level) M clean-up after an error and return to the top level
     returns M never returns

(continue) M continue from a correctable error
     returns M never returns

(errset expr [pflag]) M trap errors
     expr M the expression to execute
     pflag M flag to control printing of the error message
     returns M the value of the last expression consed with nil
     or nil on error

(baktrace [n]) M print n levels of trace back information
     n M the number of levels (defaults to all levels)
     returns M nil

(evalhook expr ehook ahook [env]) M evaluate with hooks
     expr M the expression to evaluate
     ehook M the value for *evalhook*
     ahook M the value for *applyhook*
     env M the environment (default is nil)
     returns M the result of evaluating the expression

(profile flag)(This is not a standard XLISP 2.0 function.)  M turn profiling on
     or off.
     flag M nil turns profiling off, otherwise on
     returns M the previous state of profiling.


IV.27. Arithmetic Functions
(truncate expr) M truncates a floating point number to an integer
     expr M the number
     returns M the result of truncating the number

(float expr) M converts an integer to a floating point number
     expr M the number
     returns M the result of floating the integer

(+ expr...)  M add a list of numbers
     expr M the numbers
     returns M the result of the addition

(- expr...)  M subtract a list of numbers or negate a single number
     expr M the numbers
     returns M the result of the subtraction

(* expr...)  M multiply a list of numbers
     expr M the numbers
     returns M the result of the multiplication

(/ expr...)  M divide a list of numbers
     expr M the numbers
     returns M the result of the division

(1+ expr) M add one to a number
     expr M the number
     returns M the number plus one

(1- expr) M subtract one from a number
     expr M the number
     returns M the number minus one

(rem expr...)  M remainder of a list of numbers
     expr M the numbers
     returns M the result of the remainder operation

(min expr...)  M the smallest of a list of numbers
     expr M the expressions to be checked
     returns M the smallest number in the list

(max expr...)  M the largest of a list of numbers
     expr M the expressions to be checked
     returns M the largest number in the list

(abs expr) M the absolute value of a number
     expr M the number
     returns M the absolute value of the number

(gcd n1 n2...)  M compute the greatest common divisor
     n1 M the first number (integer)
     n2 M the second number(s) (integer)
     returns M the greatest common divisor

(random n) M compute a random number between 0 and n-1 inclusive
     n M the upper bound (integer)
     returns M a random number

(rrandom) M compute a random real number between 0 and 1 inclusive
     returns M a random floating point number

(sin expr) M compute the sine of a number
     expr M the floating point number
     returns M the sine of the number

(cos expr) M compute the cosine of a number
     expr M the floating point number
     returns M the cosine of the number

(tan expr) M compute the tangent of a number
     expr M the floating point number
     returns M the tangent of the number

(atan  expr [expr2])(This is not a standard XLISP 2.0 function.)  M compute the
     arctangent
     expr M the value of x
     expr2 M the value of y (default value is 1.0)
     returns M the arctangent of x/y

(expt x-expr y-expr) M compute x to the y power
     x-expr M the floating point number
     y-expr M the floating point exponent
     returns M x to the y power

(exp x-expr) M compute e to the x power
     x-expr M the floating point number
     returns M e to the x power

(sqrt expr) M compute the square root of a number
     expr M the floating point number
     returns M the square root of the number

(< n1 n2...)  M test for less than
(<= n1 n2...) M test for less than or equal to
(= n1 n2...)  M test for equal to
(/= n1 n2...) M test for not equal to
(>= n1 n2...) M test for greater than or equal to
(> n1 n2...) M test for greater than
     n1 M the first number to compare
     n2 M the second number to compare
     returns M t if the results of comparing n1 with n2, n2 with n3, etc.,  are
          all true.


IV.28. Bitwise Logical Functions
(logand expr...) M the bitwise and of a list of numbers
     expr M the numbers
     returns M the result of the and operation

(logior expr...)  M the bitwise inclusive or of a list of numbers
     expr M the numbers
     returns M the result of the inclusive or operation

(logxor expr...)  M the bitwise exclusive or of a list of numbers
     expr M the numbers
     returns M the result of the exclusive or operation

(lognot expr) M the bitwise not of a number
     expr M the number
     returns M the bitwise inversion of number


IV.29. String Functions
(string expr) M make a string from an integer ascii value
     expr M the integer
     returns M a one character string

(string-search  pat  str  &key  :start  :end)(This  is not a standard XLISP 2.0
     function.)  M search for pattern in string
     pat M a string to search for
     str M the string to be searched
     :start M the starting offset in str
     :end M the ending offset + 1
     returns M index of pat in str or NIL if not found

(string-trim bag str) M trim both ends of a string
     bag M a string containing characters to trim
     str M the string to trim
     returns M a trimed copy of the string

(string-left-trim bag str) M trim the left end of a string
     bag M a string containing characters to trim
     str M the string to trim
     returns M a trimed copy of the string

(string-right-trim bag str) M trim the right end of a string
     bag M a string containing characters to trim
     str M the string to trim
     returns M a trimed copy of the string

(string-upcase str &key :start :end) M convert to uppercase
     str M the string
     :start M the starting offset
     :end M the ending offset + 1
     returns M a converted copy of the string

(string-downcase str &key :start :end) M convert to lowercase
     str M the string
     :start M the starting offset
     :end M the ending offset + 1
     returns M a converted copy of the string

(nstring-upcase str &key :start :end) M convert to uppercase
     str M the string
     :start M the starting offset
     :end M the ending offset + 1
     returns M the converted string (not a copy)

(nstring-downcase str &key :start :end) M convert to lowercase
     str M the string
     :start M the starting offset
     :end M the ending offset + 1
     returns M the converted string (not a copy)

(strcat expr...)  M concatenate strings
     expr M the strings to concatenate
     returns M the result of concatenating the strings

(subseq string start [end]) M extract a substring
     string M the string
     start M the starting position (zero origin)
     end M the ending position + 1 (defaults to end)
     returns M substring between start and end

(string< str1 str2 &key :start1 :end1 :start2 :end2) (string<= str1  str2  &key
     :start1 :end1 :start2 :end2)
(string= str1 str2 &key :start1 :end1 :start2 :end2)
(string/= str1 str2 &key :start1 :end1 :start2 :end2)
(string>= str1 str2 &key :start1 :end1 :start2 :end2)
(string> str1 str2 &key :start1 :end1 :start2 :end2)
     str1 M the first string to compare
     str2 M the second string to compare
     :start1 M first substring starting offset
     :end1 M first substring ending offset + 1
     :start2 M second substring starting offset
     :end2 M second substring ending offset + 1
     returns M t if predicate is true, nil otherwise
     Note: case is significant with these comparison functions.

(string-lessp str1 str2 &key :start1 :end1 :start2 :end2)
(string-not-greaterp str1 str2 &key :start1 :end1 :start2 :end2)
(string-equalp str1 str2 &key :start1 :end1 :start2 :end2)
(string-not-equalp str1 str2 &key :start1 :end1 :start2 :end2)
(string-not-lessp str1 str2 &key :start1 :end1 :start2 :end2)
(string-greaterp str1 str2 &key :start1 :end1 :start2 :end2)
     str1 M the first string to compare
     str2 M the second string to compare
     :start1 M first substring starting offset
     :end1 M first substring ending offset + 1
     :start2 M second substring starting offset
     :end2 M second substring ending offset + 1
     returns M t if predicate is true, nil otherwise
     Note: case is not significant with these comparison functions.


IV.30. Character Functions
(char string index) M extract a character from a string
     string M the string
     index M the string index (zero relative)
     returns M the ascii code of the character

(upper-case-p chr) M is this an upper case character?
     chr M the character
     returns M t if the character is upper case, nil otherwise

(lower-case-p chr) M is this a lower case character?
     chr M the character
     returns M t if the character is lower case, nil otherwise

(both-case-p chr) M is this an alphabetic (either case) character?
     chr M the character
     returns M t if the character is alphabetic, nil otherwise

(digit-char-p chr) M is this a digit character?
     chr M the character
     returns M the digit weight if character is a digit, nil otherwise

(char-code chr) M get the ascii code of a character
     chr M the character
     returns M the ascii character code (integer)

(code-char code) M get the character with a specified ascii code
     code M the ascii code (integer)
     returns M the character with that code or nil

(char-upcase chr) M convert a character to upper case
     chr M the character
     returns M the upper case character

(char-downcase chr) M convert a character to lower case
     chr M the character
     returns M the lower case character

(digit-char n) M convert a digit weight to a digit
     n M the digit weight (integer)
     returns M the digit character or nil

(char-int chr) M convert a character to an integer
     chr M the character
     returns M the ascii character code

(int-char int) M convert an integer to a character
     int M the ascii character code
     returns M the character with that code

(char< chr1 chr2...)
(char<= chr1 chr2...)
(char= chr1 chr2...)
(char/= chr1 chr2...)
(char>= chr1 chr2...)
(char> chr1 chr2...)
     chr1 M the first character to compare
     chr2 M the second character(s) to compare
     returns M t if predicate is true, nil otherwise
     Note: case is significant with these comparison functions.

(char-lessp chr1 chr2...)
(char-not-greaterp chr1 chr2...)
(char-equalp chr1 chr2...)
(char-not-equalp chr1 chr2...)
(char-not-lessp chr1 chr2...)
(char-greaterp chr1 chr2...)
     chr1 M the first string to compare
     chr2 M the second string(s) to compare
     returns M t if predicate is true, nil otherwise
     Note: case is not significant with these comparison functions.


IV.31. Input/Output Functions
(read [stream [eof [rflag]]]) M read an expression
     stream M the input stream (default is standard input)
     eof M the value to return on end of file (default is nil)
     rflag M recursive read flag (default is nil)
     returns M the expression read

(print expr [stream]) M print an expression on a new line
     expr M the expression to be printed
     stream M the output stream (default is standard output)
     returns M the expression

(prin1 expr [stream]) M print an expression
     expr M the expression to be printed
     stream M the output stream (default is standard output)
     returns M the expression

(princ expr [stream]) M print an expression without quoting
     expr M the expressions to be printed
     stream M the output stream (default is standard output)
     returns M the expression

(pprint expr [stream]) M pretty print an expression
     expr M the expressions to be printed
     stream M the output stream (default is standard output)
     returns M the expression

(terpri [stream]) M terminate the current print line
     stream M the output stream (default is standard output)
     returns M nil

(flatsize expr) M length of printed representation using prin1
     expr M the expression
     returns M the length

(flatc expr) M length of printed representation using princ
     expr M the expression
     returns M the length


IV.32. The Format Function
(format stream fmt arg...)  M do formated output
     stream M the output stream
     fmt M the format string
     arg M the format arguments
     returns M output string if stream is nil, nil otherwise

  The  format  string  can contain characters that should be copied directly to
the output and formatting directives.  The formatting directives are:

    ~A M print next argument using princ
    ~S M print next argument using prin1
    ~% M start a new line
    ~~ M print a tilde character
    ~<newline> M ignore this one newline and white space on the
    next line up to the first non-white-space character or newline. This
    allows strings to continue across multiple lines

IV.33. File I/O Functions
  Note that files are ordinarily opened as text. Binary files (such as standard
midi files) must be opened with open-binary on non-unix systems.
(open fname &key :direction) M open a file stream
     fname M the file name string or symbol
     :direction M :input or :output (default is :input)
     returns M a stream

(open-binary fname &key :direction) M open a binary file stream
     fname M the file name string or symbol
     :direction M :input or :output (default is :input)
     returns M a stream

(close stream) M close a file stream
     stream M the stream
     returns M nil

(setdir  path)(This  is  not  a  standard  XLISP  2.0  function.) M set current
     directory
     path M the path of the new directory
     returns M the resulting full path, e.g.  (setdir  ".")  gets  the  current
          working directory, or nil if an error occurs

(listdir  path)(This  is  not a standard XLISP 2.0 function.) M get a directory
     listing
     path M the path of the directory to be listed
     returns M list of filenames in the directory

(get-temp-path)(This is not a standard XLISP 2.0 function.) M get a path  where
     a  temporary  file  can  be  created.  Under  Windows,  this  is  based on
     environment variables. If XLISP is running as a sub-process to  Java,  the
     environment  may  not  exist,  in  which  case  the  default result is the
     unfortunate choice c:\windows\.
     returns M the resulting full path as a string

(read-char [stream]) M read a character from a stream
     stream M the input stream (default is standard input)
     returns M the character

(peek-char [flag [stream]]) M peek at the next character
     flag M flag for skipping white space (default is nil)
     stream M the input stream (default is standard input)
     returns M the character (integer)

(write-char ch [stream]) M write a character to a stream
     ch M the character to write
     stream M the output stream (default is standard output)
     returns M the character

(read-int [stream [length]]) M read a binary integer from a stream
     stream M the input stream (default is standard input)
     length M the length of the integer in bytes (default is 4)
     returns M the integer
     Note: Integers are assumed to be big-endian (high-order  byte  first)  and
          signed, regardless of the platform. To read little-endian format, use
          a negative number for  the  length,  e.g.  -4  indicates  a  4-bytes,
          low-order byte first. The file should be opened in binary mode.

(write-int ch [stream [length]]) M write a binary integer to a stream
     ch M the character to write
     stream M the output stream (default is standard output)
     length M the length of the integer in bytes (default is 4)
     returns M the integer
     Note:  Integers  are  assumed to be big-endian (high-order byte first) and
          signed, regardless of the platform. To write in little-endian format,
          use  a  negative  number for the length, e.g. -4 indicates a 4-bytes,
          low-order byte first. The file should be opened in binary mode.

(read-float [stream [length]]) M read a binary  floating-point  number  from  a
     stream
     stream M the input stream (default is standard input)
     length  M the length of the float in bytes (default is 4, legal values are
          -4, -8, 4, and 8)
     returns M the integer
     Note: Floats are assumed to be  big-endian  (high-order  byte  first)  and
          signed, regardless of the platform. To read little-endian format, use
          a negative number for  the  length,  e.g.  -4  indicates  a  4-bytes,
          low-order byte first. The file should be opened in binary mode.

(write-float  ch [stream [length]]) M write a binary floating-point number to a
     stream
     ch M the character to write
     stream M the output stream (default is standard output)
     length M the length of the float in bytes (default is 4, legal values  are
          -4, -8, 4, and 8)
     returns M the integer
     Note:  Floats  are  assumed  to  be big-endian (high-order byte first) and
          signed, regardless of the platform. To write in little-endian format,
          use  a  negative  number for the length, e.g. -4 indicates a 4-bytes,
          low-order byte first. The file should be opened in binary mode.

(read-line [stream]) M read a line from a stream
     stream M the input stream (default is standard input)
     returns M the string

(read-byte [stream]) M read a byte from a stream
     stream M the input stream (default is standard input)
     returns M the byte (integer)

(write-byte byte [stream]) M write a byte to a stream
     byte M the byte to write (integer)
     stream M the output stream (default is standard output)
     returns M the byte (integer)


IV.34. String Stream Functions
  These functions operate  on  unnamed  streams.    An  unnamed  output  stream
collects characters sent to it when it is used as the destination of any output
function.  The functions get-output-stream-string  and  string  or  a  list  of
characters.

  An  unnamed  input stream is setup with the make-string-input-stream function
and returns each character of the string when it is used as the source  of  any
input function.

(make-string-input-stream str [start [end]])
     str M the string
     start M the starting offset
     end M the ending offset + 1
     returns M an unnamed stream that reads from the string

(make-string-output-stream)
     returns M an unnamed output stream

(get-output-stream-string stream)
     stream M the output stream
     returns M the output so far as a string
     Note:  the output stream is emptied by this function

(get-output-stream-list stream)
     stream M the output stream
     returns M the output so far as a list
     Note:  the output stream is emptied by this function


IV.35. System Functions
  Note:  the  load  function  first  tries  to  load  a  file  from the current
directory. A .lsp extension is added if there is not  already  an  alphanumeric
extension following a period.  If that fails, XLISP searches the path, which is
obtained   from   the   XLISPPATH   environment   variable    in    Unix    and
HKEY_LOCAL_MACHINE\SOFTWARE\CMU\Nyquist\XLISPPATH  under  Win32. (The Macintosh
version has no search path.)
(load fname &key :verbose :print) M load a source file
     fname M the filename string or symbol
     :verbose M the verbose flag (default is t)
     :print M the print flag (default is nil)
     returns M the filename

(save fname) M save workspace to a file
     fname M the filename string or symbol
     returns M t if workspace was written, nil otherwise

(restore fname) M restore workspace from a file
     fname M the filename string or symbol
     returns M nil on failure, otherwise never returns

(dribble [fname]) M create a file with a transcript of a session
     fname M file name string or symbol (if missing, close current transcript)
     returns M t if the transcript is opened, nil if it is closed

(gc) M force garbage collection
     returns M nil

(expand num) M expand memory by adding segments
     num M the number of segments to add
     returns M the number of segments added

(alloc num) M change number of nodes to allocate in each segment
     num M the number of nodes to allocate
     returns M the old number of nodes to allocate

(info) M show information about memory usage.
     returns M nil

(room) M show memory allocation statistics
     returns M nil

(type-of expr) M returns the type of the expression
     expr M the expression to return the type of
     returns M nil if the value is nil otherwise one of the symbols:
          SYMBOL M for symbols
          OBJECT M for objects
          CONS M for conses
          SUBR M for built-in functions
          FSUBR M for special forms
          CLOSURE M for defined functions
          STRING M for strings
          FIXNUM M for integers
          FLONUM M for floating point numbers
          CHARACTER M for characters
          FILE-STREAM M for file pointers
          UNNAMED-STREAM M for unnamed streams
          ARRAY M for arrays

(peek addrs) M peek at a location in memory
     addrs M the address to peek at (integer)
     returns M the value at the specified address (integer)

(poke addrs value) M poke a value into memory
     addrs M the address to poke (integer)
     value M the value to poke into the address (integer)
     returns M the value

(bigendiap) M is this a big-endian machine?
     returns M T if this a big-endian architecture, storing the high-order byte
          of  an  integer at the lowest byte address of the integer; otherwise,
          NIL.  (This is not a standard XLISP 2.0 function.)

(address-of expr) M get the address of an xlisp node
     expr M the node
     returns M the address of the node (integer)

(exit) M exit xlisp
     returns M never returns

(setup-console) M set default console attributes
     returns M NIL
     Note: Under Windows, Nyquist normally starts up in a medium-sized  console
          window with black text and a white background, with a window title of
          ``Nyquist.'' This is normally accomplished by  calling  setup-console
          in  system.lsp.  In  Nyquist,  you can avoid this behavior by setting
          *setup-console* to NIL in your init.lsp file. If setup-console is not
          called,  Nyquist  uses  standard input and output as is. This is what
          you want if you are running Nyquist inside of emacs, for example.

(echoenabled flag) M turn console input echoing on or off
     flag M T to enable echo, NIL to disable
     returns M NIL
     Note: This function is only implemented under  Linux  and  Mac  OS  X.  If
          Nyquist I/O is redirected through pipes, the Windows version does not
          echo the input, but the Linux and Mac versions do. You can  turn  off
          echoing  with  this  function.  Under  windows  it  is  defined to do
          nothing.

IV.36. File I/O Functions



IV.36.1. Input from a File
  To open a file for input, use the open function  with  the  keyword  argument
:direction  set  to  :input.   To open a file for output, use the open function
with the keyword argument :direction set to :output.  The open function takes a
single required argument which is the name of the file to be opened.  This name
can be in the form of a string or a symbol.    The  open  function  returns  an
object  of  type  FILE-STREAM if it succeeds in opening the specified file.  It
returns the value nil if it fails.  In order to  manipulate  the  file,  it  is
necessary  to  save  the  value returned by the open function.  This is usually
done by assigning it to a variable with the setq special form or by binding  it
using let or let*.  Here is an example:

    (setq fp (open "init.lsp" :direction :input))

Evaluating  this expression will result in the file init.lsp being opened.  The
file object that will be returned by the open function will be assigned to  the
variable fp.

  It is now possible to use the file for input.  To read an expression from the
file, just supply the value of the fp variable as the optional stream  argument
to read.

    (read fp)

Evaluating this expression will result in reading the first expression from the
file init.lsp.  The expression will be returned  as  the  result  of  the  read
function.    More  expressions can be read from the file using further calls to
the read function.  When there are  no  more  expressions  to  read,  the  read
function will return nil (or whatever value was supplied as the second argument
to read).

  Once you are done reading from the file, you should close it.  To  close  the
file, use the following expression:

    (close fp)

Evaluating this expression will cause the file to be closed.



IV.36.2. Output to a File
  Writing  to  a file is pretty much the same as reading from one.  You need to
open the file first.  This time you should use the open  function  to  indicate
that you will do output to the file.  For example:

    (setq fp (open "test.dat" :direction :output))

Evaluating this expression will open the file test.dat for output.  If the file
already exists, its current contents will be discarded.  If it doesn't  already
exist,  it will be created.  In any case, a FILE-STREAM object will be returned
by the OPEN function.  This file object will be assigned to the fp variable.

  It is now possible to write to this file by supplying the  value  of  the  fp
variable as the optional stream parameter in the print function.
    (print "Hello there" fp)

Evaluating  this  expression  will  result  in the string ``Hello there'' being
written to the file test.dat.  More data can be written to the file  using  the
same technique.

  Once  you  are  done  writing  to  the file, you should close it.  Closing an
output file is just like closing an input file.

    (close fp)

Evaluating this expression will close the output file and make it permanent.



IV.36.3. A Slightly More Complicated File Example
  This example shows how to open a file, read each  Lisp  expression  from  the
file  and  print  it.    It  demonstrates  the  use of files and the use of the
optional stream argument to the read function.

    (do* ((fp (open "test.dat" :direction :input))
          (ex (read fp) (read fp)))
         ((null ex) nil)
      (print ex))
                                  REFERENCES

[Dannenberg 89]
               Dannenberg, R. B. and C. L. Fraley.  Fugue: Composition and
Sound Synthesis With Lazy Evaluation and Behavioral Abstraction.  In T. Wells
and D. Butler (editor), Proceedings of the 1989 International Computer Music
Conference, pages 76-79.  International Computer Music Association, San
Francisco, 1989.

[Touretzky 84] Touretzky, David S.  LISP: a gentle introduction to symbolic
computation.  Harper & Row, New York, 1984.
Index


                          Buzz   15                 Environment   4
!   27                                              Eq   57
!Call   31                Call command   31         Eq-band   17
!Clock   30               Car   56                  Eq-highshelf   17
!csec   29                Case   27, 57             Eq-lowshelf   17
!Def   30                 Catch   58                Eql   57
!End   31                 Cauchy distribution   36  Equal   57
!msec   29                Cdr   56                  Equalization   17, 42
!Ramp   30                Cerror   58               Error   58
!Rate   28                Change directory   60     Error Handling   58
!Seti   31                Char   59                 Errors   iii
!Setv   31                Char-code   59            Errset   58
!Tempo   28               Char-downcase   60        Estimate frequency   18
                          Char-equalp   60          Eval   55
#  (Adagio   articulation)Char-greaterp   60        Eval pattern   35
        28                Char-int   60             Evalhook   58
#define'd macros   50     Char-lessp   60           Evaluation functions   55
                          Char-not-equalp   60      Evaluator   53
%   (Adagio   thirtysecondChar-not-greaterp   60    Evenp   57
        note)   27        Char-not-lessp   60       Event-dur   39
                          Char-upcase   60          Event-end   39
*   58                    Char/=   60               Event-expression   39
*A4-Hertz*   12, 25       Char<   60                Event-get-attr   39
*applyhook*   55          Char<=   60               Event-has-attr   39
*autonorm*   25           Char=   60                Event-set-attr   39
*autonorm-max-samples*    Char>   60                Event-set-dur   39
        25                Char>=   60               Event-set-expression   39
*autonorm-previous-peak*  Character Functions   59  Event-set-time   39
        25                Characterp   57           Event-time   39
*autonorm-target*   25    Chorus   21, 42           Exclamation point   27
*autonorm-type*   25      Clarinet   13             Exit   61
*autonormflag*   25       Clarinet sound   3        Exp   59
*breakenable*   25, 53, 55Clarinet-all   13         Exp-dec   13
*control-srate*    4,  18,Clarinet-freq   13        Expand   61
        25                Class   55                Exponent   33
*debug-io*   55           Class class   55          Exponential   17
*default-control-srate*   Clean-up   58             Exponential   distribution
        25                Clip   8, 17, 21                  36
*default-plot-file*   20  Clipping repair   42      Exponential envelope   13
*default-sf-dir*   19, 25 Clock   30                Expr-get-attr   39
*default-sf-format*   25  Clock command   30        Expr-has-attr   39
*default-sf-srate*     19,Close   60                Expr-set-attr   39
        25                Co-termination   20       Expression pattern   35
*default-sound-srate*   25Code-char   60            Expt   59
*error-output*   55       Comb filter   16          Extending Xlisp   50
*evalhook*   55           Combination   18          Extract   18
*file-separator*   25     Command Loop   53
*float-format*   55       Commas   29               F (Adagio dynamic)   28
*gc-flag*   55            Comment   27              F (Adagio Flat)   27
*gc-hook*   55            Compose   21              Fast   fourier   transform
*integer-format*   55     Compress   42                     tutorial   26
*loud*   4                Compress-map   42         Fboundp   57
*obarray*   55            Compressor   12           Feedback-delay   16
*plotscript-file*   20    Concatenate strings   59  Feel factor   40
*print-case*   55         Cond   57                 FF (Adagio dynamic)   28
*readtable*   54, 55      Configure nyquist   1     FFF (Adagio dynamic)   28
*rslt*   25, 50           Congen   16               Fft   26
*sound-srate*   4, 18, 25 Cons   56                 Fft tutorial   26
*soundenable*   25        Console, XLISP   61       File  I/O  Functions   60,
*standard-input*   55     Consp   57                        61
*standard-output*   55    Const   13                Filep   57
*start*   4               Constant function   13    Filter example   9
*stop*   4                Continue   58             Find string   59
*sustain*   4             Continuous-control-warp   FIR filter   16
*table*   25                      18                First   56
*trace-output*   55       Continuous-sound-warp   18First derivative   14
*tracelimit*   53, 55     Contour generator   16    Flange effect   42
*tracelist*   55          Control   13              Flat   27
*tracenable*   25, 53, 55 Control change   29       Flatc   60
*transpose*   4           Control characters,  XLISPFlatsize   60
*unbound*   55                    53                Flet   57
*warp*   4, 18            Control Constructs   57   Float   58
                          Control-srate-abs   18    Floatp   57
+   58                    Control-warp   13         Flute sound   3
                          Convert   sound  to  arrayFM synthesis   9
, (Adagio)   29                   12                Fmlfo   13
                          Convolution   16          Fmosc   14
-   58                    Copier pattern   35       Follow   12
                          Cos   59                  Follower   21
. (Adagio)   27           Cue   13                  Force-srate   13
                          Cue-file   13             Format   60
/   58                    Current-path   33         Fourth   56
/=   59                   Cxxr   56                 Frequency analysis   18
                          Cxxxr   56                Frequency Modulation   9
1+   58                   Cxxxxr   56               Full path name   33
1-   58                   Cycle pattern   34        Funcall   55
                                                    Function   55
:answer   55              Data Types   53           Fundamenal       frequency
:class   55               Db-average   42                   estimation   18
:isnew   55               Db-to-linear   12
:new   55                 DB0   3                   Gain   42
:show   55                DB1   3                   Gate   12, 21
                          DB10   3                  Gaussian distribution   37
; (Adagio)   29           Debugging   12, 20, 33, 58Gc   61
                          Decf   33                 Gcd   59
<   59                    Decrement   33            GEN05   16
<=   59                   Default durations   28    Gensym   55
                          Default   28              Geometric     distribution
=   59                    Default sample rate   5           37
                          Default     sound     fileGet   56
>   59                            directory   19    Get char   60
>=   59                   Default time   27         Get-duration   12
                          Defining Behaviors   5    Get-lambda-expression   55
A440   12                 Defmacro   55             Get-loud   12
Abs   59                  Defun   55                Get-output-stream-list
Abs-env   18              Delay   16                        61
Absolute value   17, 21   Delay, variable   21      Get-output-stream-string
Access samples   11       Delete   56                       61
Accidentals   27          Delete-if   57            Get-slider-value   21
Accumulate pattern   35   Delete-if-not   57        Get-sustain   12
Adagio   27               Demos, bell sound   3     Get-temp-path   60
Add offset to sound   21  Demos, distortion   16    Get-transpose   12
Add to file samples   20  Demos, drum sound   3     Get-warp   12
Add-action-to-workspace   Demos, fft   26           Global Variables   25
        40                Demos, FM   9             Go   58
Add-to-workspace   40     Demos, FM synthesis   3   Gong sounds   3
Additive synthesis,  gongsDemos, formants   3       Granular synthesis   43
        3                 Demos, gong sound   3     Graphical equalizer   42
Address-of   61           Demos, lpc   32           Grindef   33
Aftertouch   29           Demos, midi   27
Agc   42                  Demos, piano   42         H (Adagio Half note)   27
Algorithmic    CompositionDemos, pitch change   21  H   3
        34                Demos,   rhythmic  patternHalf note   3, 27
All pass filter   16              3                 Hash   56
Alloc   61                Demos, ring modulation   3Hd   3
Allpass2   17             Demos,    sample-by-sampleHeader file format   50
Allpoles-from-lpc   32            3                 Heap pattern   35
Alpass filter   16        Demos,   scratch  tutorialHigh-pass filter   16
Amosc   14                        9                 Highpass2   16
Analog synthesizer   43   Demos, Shepard tones   16 Highpass4   17
And   57                  Demos,  spectral  analysisHighpass6   17
Append   56                       of a chord   3    Highpass8   17
Apply   55                Demos,   voice   synthesisHp   16
Apply-banded-bass-boost           16                Ht   3
        43                Demos, wind sound   9     Hyperbolic          cosine
Apply-banded-delay   43   Derivative   14                   distribution   36
Apply-banded-treble-boost Describe   40             Hz-to-step   12
        43                Destructive List FunctionsHzosc   14
Approximation   15                56
Arc sine distribution   37Developing code   33      I (Adagio eIght note)   27
Aref   56                 Diff   19                 I   3
Areson   16               Difference   41           Id   3
Args   33                 Difference of sounds   19 If   57
Arguments   to   a    lispDigit-char   60           Ifft   26
        function   33     Digit-char-p   59         Incf   33
Arithmetic Functions   58 Directory listing   60    Increment   33
Array from sound   12     Directory,  default  soundInfo   61
Array Functions   56              file   19         Input from a File   61
Arrayp   57               Distortion tutorial   16  Input/Output     Functions
Articulation   27, 28     Distributions, probability        60
Assoc   56                        36                Installation   1
Asterisk   27             Division   17             Int-char   60
At   18                   Do   58                   Integerp   57
At Transformation   5     Do*   58                  Integrate   14
Atan   59                 Dolby Pro-Logic   43      Intern   55
Atom   57                 Dolby Surround   43       Interpolate   40
Atone   16                Dolist   58               Intersection   40
Attributes   27           Doppler effect   43       Intgen   50
Automatic   gain   controlDot   27                  Inverse   21
        42                Dotimes   58              Inverse fft   26
Autonorm-off   8, 19      Dotted durations   3      It   3
Autonorm-on   8, 19       Dribble   61
Average   21              Drum sound   3            Jitter   40
                          DSP in Lisp   3
Backquote   55            Dtmf   43                 K (Adagio control)   29
Backward   42             Dtmf-tone   43            Karplus-Strong   15
Baktrace   58             Dubugging   21            Karplus-Strong   synthesis
Banded bass boost   43    Duration   27                     3
Banded delay   43         Duration notation   3     Keyword parameters   38
Banded treble boost   43  Duration  of another sound
Bandfx.lsp   42                   20                Labels   57
Bandpass filter   16      DX7   27                  Lambda   55
Bandpass2   17            Dynamic markings   28     Lambda Lists   54
Bartok   29                                         Last   56
Behavioral abstraction   4Echo   16                 Latency   13
Behaviors   13            Echoenabled   61          Legato   18, 28
Bell sound   3            Effect, chorus   42       Length   56
Bernoulli     distributionEffect, flange   42       Length pattern   35
        37                Effect, reverberation   43Let   57
Beta distribution   37    Effect, stereo   43       Let*   57
Big endian   61           Effect, stereo pan   43   Lexical conventions   53
Bigendiap   61            Effect, swap channels   43LF (Adagio dynamic)   28
Bilateral      exponentialEffect, widen   43        Lf   3
        distribution   36 Effects, phaser   42      LFF (Adagio dynamic)   28
Binary files   60         EIghth note   3, 27       Lff   3
Binomial distribution   37Emacs, using Nyquist  withLFFF (Adagio dynamic)   28
Biquad   16                       61                Lfff   3
Biquad-m   16             End command   31          Lfo   13
Bitwise Logical  FunctionsEndian   61               Libraries   42
        59                Endless tones   3         Limit   17
Blank   27                Endp   57                 Limiter   12
Block   58                Env   2, 13               Line pattern   34
Both-case-p   59          Env-note   2              Linear distribution   36
Boundp   2, 57            Envelope   2              Linear interpolation   40
Brass sound   3           Envelope follower   12, 21Linear Prediction   32
Break   53, 58            Envelope generator   16   Linear prediction tutorial
Build-harmonic   2, 13    Envelopes   2                     32
Linear-to-db   12         Pattern, product   35     Score-gen   38
Lisp DSP   3              Pattern, random   34      Score-get-begin   39
Lisp Include Files   51   Pattern, sum   35         Score-get-end   39
List   56                 Patternp   40             Score-indexof   40
List directory   60       Peak amplitude   8        Score-last-indexof   40
List Functions   56       Peak,  maximum   amplitudeScore-merge   39
Listdir   60                      21                Score-must-have-begin-end
Listing of  lisp  functionPeek   61                         39
        33                Peek-char   60            Score-play   40
Listp   57                Period estimation   18    Score-print   40
Little endian   61        Phaser   42               Score-randomize-start   40
LMF (Adagio dynamic)   28 Physical model   3        Score-read-smf   40
Lmf   3                   Piano synthesizer   42    Score-repeat   39
LMP (Adagio dynamic)   28 Piano synthesizer tutorialScore-scale   39
Lmp   3                           42                Score-select   39
Load   61                 Piano-midi   42           Score-set-begin   39
Local-to-global   12      Piano-midi2file   42      Score-set-end   39
Log function   12         Piano-note   42           Score-shift   39
Logand   59               Piano-note-2   42         Score-sort   39
Logical-stop   11         Piece-wise   15           Score-sorted   39
Logior   59               Piece-wise linear   22    Score-stretch   39
Logistic distribution   36Pitch   27                Score-stretch-to-length
Lognot   59               Pitch bend   29                   40
Logorithm   17            Pitch detection   18      Score-sustain   39
Logxor   59               Pitch notation   3        Score-transpose   39
Loop   58                 Pitch shifting   21       Score-voice   39
Looping Constructs   58   Pl-center   43            Score-write-smf   40
Loud   18                 Pl-doppler   43           Scratch sound   9
Loudness   27, 28         Pl-left   43              Sd   3
Low-frequency   oscillatorPl-pan2d   43             Search path   1
        13                Pl-position   43          Second   56
Low-pass filter   16, 23  Pl-right   43             Sections, Adagio   29
Lower-case-p   59         Play   2, 19              Semicolon, Adagio   29
Lowpass2   16             Play in reverse   42      Seq   18
Lowpass4   17             Play-file   8, 19         Seqrep   18
Lowpass6   17             Pluck   15                Sequences   2, 27
Lowpass8   17             Plucked string   15       Sequence_example.htm   2
LP (Adagio dynamic)   28  Plusp   57                Sequential behavior   4
Lp   3, 16                Poisson distribution   37 Set   55
LPC   32                  Poke   61                 Set intersection   40
Lpc tutorial   32         Polyrhythm   30           Set union   40
Lpc-frame-err   32        Pop   33                  Set-control-srate   5, 12
Lpc-frame-filter-coefs    Portamento switch   29    Set-difference   41
        32                Power   33                Set-logical-stop   19
Lpc-frame-rms1   32       PP (Adagio dynamic)   28  Set-pitch-names   12
Lpc-frame-rms2   32       PPP (Adagio dynamic)   28 Set-sound-srate   5, 12
LPP (Adagio dynamic)   28 Pprint   60               Setdir   60
Lpp   3                   Predicate Functions   57  Setf   55
LPPP (Adagio dynamic)   28Preset   28               Seti commnad   31
Lppp   3                  Prin1   60                Setq   55
Lpreson   32              Princ   60                Setup nyquist   1
                          Print   60                Setup-console   61
M (Adagio control)   29   Print midi file   43      Setv command   31
Macroexpand   55          Probability  distributionsSf-info   20
Macroexpand-1   55                36                Shape   16
Macrolet   57             Prod   13                 Sharp   27
Make-accumulate   35      Product pattern   35      Shepard tones   3, 16
Make-array   56           Product   19              Shift-time   14
Make-copier   35          Profile   58              Show midi file   43
Make-cycle   34           Profiling   55            Show-lpc-data   32
Make-eval   35            Prog   58                 Signal  composition    21,
Make-heap   35            Prog*   58                        22
Make-length   35          Prog1   58                Signal multiplication   22
Make-line   34            Prog2   58                Signal-start   11
Make-lpanal-iterator   32 Progn   58                Signal-stop   11
Make-lpc-file-iterator    Program   29              Sim   2, 18
        32                Program change   27       Simrep   18
Make-markov   35          Progv   58                Simultaneous Behavior   4
Make-palindrome   34      Property   List  FunctionsSin   59
Make-product   35                 56                Sine   14
Make-random   34          Psetq   55                Siosc   15
Make-string-input-stream  Pulse oscillator   14     Sixteenth note   3, 27
        61                Pulse-width     modulationSixtyfourth note   27
Make-string-output-stream         14                Slope   14
        61                Push   33                 Smooth   14
Make-sum   35             Putprop   56              Snd-abs   21
Make-symbol   55          Pwe   15                  Snd-add   21
Make-window   35          Pwe-list   15             Snd-allpoles   32
Maketable   13            Pwer   16                 Snd-alpass   22
Manipulation   of   scoresPwer-list   16            Snd-alpasscv   22
        39                Pwev   15                 Snd-alpassvv   22
Mapc   56                 Pwev-list   16            Snd-amosc   23
Mapcar   56               Pwevr   16                Snd-areson   22
Mapl   56                 Pwevr-list   16           Snd-aresoncv   22
Maplist   56              Pwl   15                  Snd-aresonvc   22
Markov analysis   35      Pwl-list   15             Snd-aresonvv   22
Markov pattern   35       Pwlr   15                 Snd-atone   22
Markov-create-rules   35  Pwlr-list   15            Snd-atonev   22
Max   59                  Pwlv   15                 Snd-avg   21
Maximum   17, 59          Pwlv-list   15            Snd-biquad   22
Maximum amplitude   8, 22 Pwlvr   15                Snd-buzz   23
Maximum of two sounds   22Pwlvr-list   15           Snd-chase   23
Member   56                                         Snd-clarinet   23
Memory usage   12         Q  (Adagio  Quarter  note)Snd-clarinet-all   24
MF (Adagio dynamic)   28          27                Snd-clarinet-freq   23
Middle C   27             Q   3                     Snd-clip   21
MIDI   27                 Qd   3                    Snd-compose   21
MIDI Clock   30           Qt   3                    Snd-congen   23
MIDI file   40            Quantize   17             Snd-const   20
MIDI program   28         Quarter note   3, 27      Snd-convolve   23
Midi-show   43            Quote   55                Snd-copy   21
Midi-show-file   43                                 Snd-coterm   20
Mikrokosmos   29          R (Adagio Rest)   27      Snd-delay   23
Min   58                  Ramp   17                 Snd-down   21
Minimoog   43             Random   33, 36, 59       Snd-exp   21
Minimum   17, 58          Random pattern   34       Snd-extent   11
Minusp   57               Rate   27, 28             Snd-fetch   11
Mix   19                  Read   60                 Snd-fetch-array   11
Mix to file   20          Read directory   60       Snd-fft   26
Mkwave   2                Read macros   54          Snd-flatten   11
Modulation wheel   29     Read samples   11         Snd-fmosc   23
Modulo (rem) function   58Read  samples  from   fileSnd-follow   21
Mono to stereo   43               19                Snd-from-array   11
Moog   43                 Read  samples  in  reverseSnd-fromarraystream   11
Moving average   21               42                Snd-fromobject   11
MP (Adagio dynamic)   28  Read-byte   61            Snd-gate   21
Mult   2, 13, 19          Read-char   60            Snd-ifft   26
Multichannel Sounds   11  Read-float   60           Snd-inverse   21
Multiple band effects   42Read-int   60             Snd-length   11
Multiple commands   29    Read-line   60            Snd-log   21
Multiple tempi   30       Readtables   54           Snd-lpanal   32
Multiplication   22       Real-random   33          Snd-lpreson   32
Multiply signals   19     Recip   17                Snd-max   22
                          Reciprocal   17           Snd-maxsamp   11
N (Adagio Next)   27      Registry   1              Snd-maxv   22
Natural   27              Rem   58                  Snd-multiseq   24
Natural log   17          Remainder   58            Snd-normalize   22
Nband   42                Remove   56               Snd-offset   21
Nband-range   42          Remove-if   56            Snd-oneshot   22
Nconc   56                Remove-if-not   56        Snd-osc   23
Nested Transformations   5Remprop   56              Snd-overwrite   20
Next Adagio command   27  Replace file samples   20 Snd-partial   23
Next in pattern   34      Resample   13             Snd-play   11
Next pattern   34         Resampling   13, 21       Snd-pluck   23
Noise   18                Rescaling   8             Snd-print   12
Noise gate   21           Resolution   29           Snd-print-tree   12, 20
Noise-gate   12           Reson   16                Snd-prod   22
Normalization   8         Rest   17, 56             Snd-pwl   22
Not   57                  Restore   61              Snd-quantize   22
Not   enough   memory  forRests   27                Snd-read   20
        normalization   8 Return   58               Snd-recip   22
Notch filter   16         Return-from   58          Snd-resample   22
Notch2   17               Reverb   43               Snd-resamplev   22
Note   2                  Reverse   56              Snd-reson   23
Note list   19            Reverse, sound   42       Snd-resoncv   23
Nstring-downcase   59     Ring modulation   3       Snd-resonvc   23
Nstring-upcase   59       Risset   3                Snd-resonvv   23
Nth   56                  Rms   17, 21              Snd-samples   12
Nthcdr   56               Room   61                 Snd-save   20
Null   57                 Rplaca   56               Snd-sax   24
Numberp   57              Rplacd   56               Snd-sax-all   24
Ny:all   3                Rrandom   59              Snd-sax-freq   24
                                                    Snd-scale   22
O (Adagio control)   29   S (Adagio Sharp)   27     Snd-seq   24
Object   55               S (Adagio Sixteenth  note)Snd-set-latency   13
Object Class   55                 27                Snd-set-logical-stop   12
Objectp   57              S   3                     Snd-shape   22
Objects   54              S-abs   17                Snd-sine   23
Octave specification   27 S-add-to   20             Snd-siosc   23
Oddp   57                 S-exp   17                Snd-slider-snd   21
Offset   40               S-log   17                Snd-sqrt   21
Offset to a sound   21    S-max   8, 17             Snd-srate   12
Omissions   iii           S-min   8, 17             Snd-sref   12
Oneshot   22              S-overwrite   20          Snd-t0   12
Open   60                 S-plot   20               Snd-tapf   21
Open sound control     13,S-read   19               Snd-tapv   21
        49                S-rest   17               Snd-time   12
Or   57                   S-reverse   42            Snd-tone   23
Osc   2, 13, 14           S-save   19               Snd-tonev   23
Osc-note   17             S-sqrt   17               Snd-trigger   24
Osc-pulse   14            Sample interpolation   22 Snd-xform   22
Osc-saw   14              Sample rate, forcing   13 Snd-yin   22
Osc-tri   14              Sample rates   5          Snd-zero   21
Output   samples  to  fileSampler   15              Soften-clipping   42
        19                Samples   11, 12          Sort   57
Output to a File   61     Samples, reading   11     Sound   13
Overlap   18              Sampling rate   12           accessing point   11
Overwrite samples   20    Save   61                    creating   from   array
                          Save samples to file   19         11
P (Adagio dynamic)   28   Save-lpc-file   32        Sound    file    directory
P (Adagio Pitch)   27     Save-workspace   40               default   19
Palindrome pattern   34   Saving Sound Files   8    Sound file i/o   8, 19
Pan   13, 43              Sawtooth oscillator   14  Sound file info   20
Pan, stereo   43          Sawtooth wave   2         Sound from Lisp data   11
Parameters, keyword   38  Sax   13, 14              Sound-off   19
Params-scale   40         Sax-all   14              Sound-on   19
Params-transpose   40     Sax-freq   13             Sound-srate-abs   18
Partial   14              Scale   2, 14             Sound-warp   14
Path, current   33        Scale-db   14             Soundfilename   20
Pattern, eval   35        Scale-srate   14          Soundp   12
Pattern, length   35      Scan directory   60       Sounds   11
Pattern, window   35      Score   19                Sounds vs. Behaviors   4
Pattern, accumulate   35  Score manipulation   39   Spatialization   43
Pattern, copier   35      Score, musical   2        Special command   27
Pattern, cycle   34       Score-adjacent-events   40Spectral     interpolation
Pattern, expression   35  Score-append   39                 15
Pattern, heap   35        Score-apply   40          Speed-dial   43
Pattern, line   34        Score-filter   39         Splines   15
Pattern, markov   35      Score-filter-length   39  Sqrt   59
Pattern, palindrome   34  Score-filter-overlap   40 Square oscillator   14
Square root   17, 21
Srate   11
Sref   11
Sref-inverse   11
St   3
Stacatto   18
Staccato   28
Stack trace   58
Standard MIDI File   40
Stats   12
Step-to-hz   12
Stereo   43
Stereo pan   43
Stereo panning   13
Stereo-chorus   42
Stereoize   43
Stk clarinet   13
Stk sax   13, 14
Stochastic functions   36
Strcat   59
Streamp   57
Stretch   3, 18
Stretching  Sampled Sounds
        8
String   59
String Functions   59
String  Stream   Functions
        61
String synthesis   15
String-downcase   59
String-equalp   59
String-left-trim   59
String-lessp   59
String-not-equalp   59
String-not-greaterp   59
String-not-lessp   59
String-right-trim   59
String-search   59
String-trim   59
String-upcase   59
String/=   59
String<   59
String<=   59
String=   59
String>   59
String>=   59
Stringp   57
Sublis   56
Subseq   59
Subset   41
Subsetp   41
Subst   56
Suggestions   iii
Sum pattern   35
Sum   19
Surround Sound   43
Sustain   18
Sustain-abs   18
Swap channels   43
Symbol Functions   55
Symbol-function   56
Symbol-name   56
Symbol-plist   56
Symbol-value   56
Symbolp   57
Symbols   55
Synchronization   30
System Functions   61
SystemRoot   1

T (Adagio Triplet)   27
T   27
Table   16
Table memory   12
Tagbody   58
Tan   59
Tap   21
Tapped delay   17
Tapv   17
Temp file   60
Tempo   27, 28
Temporary files   60
Temporary    sound   files
        directory   19
Terpri   60
The Format Function   60
The Program Feature   58
Third   56
Thirtysecond note   27
Threshold   22
Throw   58
Time   27, 28
Time Structure   18
Time units   29
Timed-seq   19
Tone   16
Top-level   58
Touch tone   43
Trace   58
Transformation environment
        4
Transformations   4, 18
Transpose   18
Transpose-abs   18
Triangle oscillator   14
Triangle wave   2
Trigger   18
Trill   31
Triplet   27
Triplet durations   3
Truncate   58
Tuba   3
Tuning   12
Tutorial, FM   9
Type-of   61

U   27
Uniform random   33, 59
Union   40
Unless   57
Untrace   58
Unwind-protect   58
Upper-case-p   59

V (Adagio Voice)   28
Variable delay   17, 21
Variable-resample function
        21
Vector   56
Velocity   28
Vinal scratch   9
Vocal sound   3
Voice   27, 28
Voice synthesis   16
Volume   29

W (Adagio Whole note)   27
W   3
Warble   9
Warp   18
Warp-abs   18
Waveforms   2
Waveshaping   16
Wavetables   2
Wd   3
When   33, 57
While   33
Whole note   3, 27
Widen   43
Wind sound   9
Window initialization   61
Window pattern   35
Wind_tutorial.htm   9
Wood drum sound   3
Workspace   40
Write samples to file   19
Write-byte   61
Write-char   60
Write-float   60
Write-int   60
Wt   3

X (Adagio control)   29
XLISP Command Loop   53
XLISP Data Types   53
XLISP evaluator   53
XLISP Lexical  Conventions
        53
XLISPPATH   1
Xmusic   34

Y (Adagio control)   29
Yin   18

Z  (Adagio  program)   28,
        29
Zerop   57

^   (Adagio    sixtyfourth
        note)   27

~ (Adagio)   29
                               Table of Contents

Preface                                                                     iii

1. Introduction and Overview                                                  1

   1.1. Installation                                                          1
       1.1.1. Unix Installation                                               1
       1.1.2. Win32 Installation                                              1
           1.1.2.1. What if Nyquist functions are undefined?                  1
           1.1.2.2. SystemRoot                                                1
       1.1.3. MacOS 9 Installation                                            2
       1.1.4. MacOS X Installation                                            2
   1.2. Helpful Hints                                                         2
   1.3. Examples                                                              2
       1.3.1. Waveforms                                                       2
       1.3.2. Wavetables                                                      2
       1.3.3. Sequences                                                       2
       1.3.4. Envelopes                                                       2
       1.3.5. Piece-wise Linear Functions                                     3
   1.4. Predefined Constants                                                  3
   1.5. More Examples                                                         3

2. Behavioral Abstraction                                                     4

   2.1. The Environment                                                       4
   2.2. Sequential Behavior                                                   4
   2.3. Simultaneous Behavior                                                 4
   2.4. Sounds vs. Behaviors                                                  4
   2.5. The At Transformation                                                 5
   2.6. Nested Transformations                                                5
   2.7. Defining Behaviors                                                    5
   2.8. Sample Rates                                                          5

3. Continuous Transformations and Time Warps                                  6

   3.1. Simple Transformations                                                6
   3.2. Time Warps                                                            6
   3.3. Abstract Time Warps                                                   6
   3.4. Nested Transformations                                                7

4. More Examples                                                              8

   4.1. Stretching Sampled Sounds                                             8
   4.2. Saving Sound Files                                                    8
   4.3. Memory Space and Normalization                                        8
   4.4. Frequency Modulation                                                  9
   4.5. Building a Wavetable                                                  9
   4.6. Filter Examples                                                       9
   4.7. DSP in Lisp                                                           9

5. Nyquist Functions                                                         11

   5.1. Sounds                                                               11
       5.1.1. What is a Sound?                                               11
       5.1.2. Multichannel Sounds                                            11
       5.1.3. Accessing and Creating Sound                                   11
       5.1.4. Miscellaneous Functions                                        12
   5.2. Behaviors                                                            13
       5.2.1. Using Previously Created Sounds                                13
       5.2.2. Sound Synthesis                                                13
           5.2.2.1. Oscillators                                              14
           5.2.2.2. Piece-wise Approximations                                15
           5.2.2.3. Filter Behaviors                                         16
           5.2.2.4. More Behaviors                                           17
   5.3. Transformations                                                      18
   5.4. Combination and Time Structure                                       18
   5.5. Sound File Input and Output                                          19
   5.6. Low-level Functions                                                  20
       5.6.1. Creating Sounds                                                20
       5.6.2. Signal Operations                                              21
       5.6.3. Filters                                                        22
       5.6.4. Table-Lookup Oscillator Functions                              23
       5.6.5. Physical Model Functions                                       23
       5.6.6. Sequence Support Functions                                     24

6. Nyquist Globals                                                           25

7. Time/Frequency Transformation                                             26

8. MIDI, Adagio, and Sequences                                               27

   8.1. Specifying Attributes                                                27
       8.1.1. Time                                                           27
       8.1.2. Pitch                                                          27
       8.1.3. Duration                                                       27
       8.1.4. Next Time                                                      27
       8.1.5. Rest                                                           27
       8.1.6. Articulation                                                   28
       8.1.7. Loudness                                                       28
       8.1.8. Voice                                                          28
       8.1.9. Timbre (MIDI Program)                                          28
       8.1.10. Tempo                                                         28
       8.1.11. Rate                                                          28
   8.2. Default Attributes                                                   28
   8.3. Examples                                                             28
   8.4. Advanced Features                                                    29
       8.4.1. Time Units and Resolution                                      29
       8.4.2. Multiple Notes Per Line                                        29
       8.4.3. Control Change Commands                                        29
       8.4.4. Multiple Tempi                                                 30
       8.4.5. MIDI Synchronization                                           30
       8.4.6. System Exclusive Messages                                      30
       8.4.7. Control Ramps                                                  30
       8.4.8. The !End Command                                               31
       8.4.9. Calling C Routines                                             31
       8.4.10. Setting C Variables                                           31

9. Linear Prediction Analysis and Synthesis                                  32

   9.1. LPC Classes and Functions                                            32
   9.2. Low-level LPC Functions                                              32

10. Developing and Debugging in Nyquist                                      33

   10.1. Debugging                                                           33
   10.2. Useful Functions                                                    33

11. Xmusic and Algorithmic Composition                                       34

   11.1. Xmusic Basics                                                       34
   11.2. Pattern Classes                                                     34
       11.2.1. cycle                                                         34
       11.2.2. line                                                          34
       11.2.3. random                                                        34
       11.2.4. palindrome                                                    34
       11.2.5. heap                                                          35
       11.2.6. copier                                                        35
       11.2.7. accumulate                                                    35
       11.2.8. sum                                                           35
       11.2.9. product                                                       35
       11.2.10. eval                                                         35
       11.2.11. length                                                       35
       11.2.12. window                                                       35
       11.2.13. markov                                                       35
   11.3. Random Number Generators                                            36
   11.4. Score Generation and Manipulation                                   38
       11.4.1. Keyword Parameters                                            38
       11.4.2. Using score-gen                                               38
       11.4.3. Score Manipulation                                            39
       11.4.4. Xmusic and Standard MIDI Files                                40
       11.4.5. Workspaces                                                    40
       11.4.6. Utility Functions                                             40

12. Nyquist Libraries                                                        42

   12.1. Piano Synthesizer                                                   42
   12.2. Dymanics Compression                                                42
   12.3. Clipping Softener                                                   42
   12.4. Graphical Equalizer                                                 42
   12.5. Sound Reversal                                                      42
   12.6. Time Delay Functions                                                42
   12.7. Multiple Band Effects                                               42
   12.8. Granular Synthesis                                                  43
   12.9. MIDI Utilities                                                      43
   12.10. Reverberation                                                      43
   12.11. DTMF Encoding                                                      43
   12.12. Dolby Surround(R), Stereo and Spatialization Effects               43
   12.13. Minimoog-inspired Synthesis                                        43
       12.13.1. Oscillator Parameters                                        44
       12.13.2. Noise Parameters                                             44
       12.13.3. Filter Parameters                                            44
       12.13.4. Amplitude Parameters                                         44
       12.13.5. Other Parameters                                             44
       12.13.6. Input Format                                                 44
       12.13.7. Sample Code/Sounds                                           44

I. Extending Nyquist                                                         46

   I.1. Translating Descriptions to C Code                                   46
   I.2. Rebuilding Nyquist                                                   46
   I.3. Accessing the New Function                                           46
   I.4. Why Translation?                                                     46
   I.5. Writing a .alg File                                                  46
   I.6. Attributes                                                           46
   I.7. Generated Names                                                      48
   I.8. Scalar Arguments                                                     48

II. Open Sound Control and Nyquist                                           49

   II.1. Sending Open Sound Control Messages                                 49
   II.2. The ser-to-osc Program                                              49

III. Intgen                                                                  50

       III.0.1. Extending Xlisp                                              50
   III.1. Header file format                                                 50
   III.2. Using #define'd macros                                             50
   III.3. Lisp Include Files                                                 51
   III.4. Example                                                            51
   III.5. More Details                                                       51

IV. XLISP: An Object-oriented Lisp                                           52

   IV.1. Introduction                                                        53
   IV.2. A Note From The Author                                              53
   IV.3. XLISP Command Loop                                                  53
   IV.4. Special Characters                                                  53
   IV.5. Break Command Loop                                                  53
   IV.6. Data Types                                                          53
   IV.7. The Evaluator                                                       53
   IV.8. Lexical Conventions                                                 53
   IV.9. Readtables                                                          54
   IV.10. Lambda Lists                                                       54
   IV.11. Objects                                                            54
   IV.12. The ``Object'' Class                                               55
   IV.13. The ``Class'' Class                                                55
   IV.14. Profiling                                                          55
   IV.15. Symbols                                                            55
   IV.16. Evaluation Functions                                               55
   IV.17. Symbol Functions                                                   55
   IV.18. Property List Functions                                            56
   IV.19. Array Functions                                                    56
   IV.20. List Functions                                                     56
   IV.21. Destructive List Functions                                         56
   IV.22. Predicate Functions                                                57
   IV.23. Control Constructs                                                 57
   IV.24. Looping Constructs                                                 58
   IV.25. The Program Feature                                                58
   IV.26. Debugging and Error Handling                                       58
   IV.27. Arithmetic Functions                                               58
   IV.28. Bitwise Logical Functions                                          59
   IV.29. String Functions                                                   59
   IV.30. Character Functions                                                59
   IV.31. Input/Output Functions                                             60
   IV.32. The Format Function                                                60
   IV.33. File I/O Functions                                                 60
   IV.34. String Stream Functions                                            61
   IV.35. System Functions                                                   61
   IV.36. File I/O Functions                                                 61
       IV.36.1. Input from a File                                            61
       IV.36.2. Output to a File                                             61
       IV.36.3. A Slightly More Complicated File Example                     62

Index                                                                        64
                                List of Figures
   Figure 1:   An envelope generated by the env function.                     3
   Figure 2:   The result of (warp4), intended to map 4 seconds of score      6
               time into 4 seconds of real time.  The function extends
               beyond 4 seconds (the dashed lines) to make sure the
               function is well-defined at location (4, 4).  Nyquist
               sounds are ordinarily open on the right.
   Figure 3:   When (warp4) is applied to (tone-seq-2), the note onsets       6
               and durations are warped.
   Figure 4:   When (warp4) is applied to (tone-seq-3), the note onsets       7
               are warped, but not the duration, which remains a constant
               0.25 seconds.  In the fast middle section, this causes
               notes to overlap.  Nyquist will sum (mix) them.
   Figure 5:   The shift-time function shifts a sound in time according to   14
               its shift argument.
   Figure 6:   Ramps generated by pwl and ramp functions.  The pwl version   17
               ramps toward the breakpoint (1, 1), but in order to ramp
               back to zero at breakpoint (1, 0), the function never
               reaches an amplitude of 1.  If used at the beginning of a
               seq construct, the next sound will begin at time 1.  The
               ramp version actually reaches breakpoint (1, 1); notice
               that it is one sample longer than the pwl version.  If used
               in a sequence, the next sound after ramp would start at
               time 1 + P, where P is the sample period.
   Figure 7:   The Linear Distribution, g = 1.                               36
   Figure 8:   The Exponential Distribution, delta = 1.                      36
   Figure 9:   The Gamma Distribution, nu = 4.                               36
   Figure 10:   The Bilateral Exponential Distribution.                      36
   Figure 11:   The Cauchy Distribution, tau = 1.                            36
   Figure 12:   The Hyperbolic Cosine Distribution.                          36
   Figure 13:   The Logistic Distribution, alpha = 1, beta = 2.              37
   Figure 14:   The Arc Sine Distribution.                                   37
   Figure 15:   The Gauss-Laplace (Gaussian) Distribution, xmu = 0, sigma    37
                = 1.
   Figure 16:   The Beta Distribution, alpha = .5, beta = .25.               37
   Figure 17:   The Bernoulli Distribution, px1 = .75.                       37
   Figure 18:   The Binomial Distribution, n = 5, p = .5.                    37
   Figure 19:   The Geometric Distribution, p = .4.                          37
   Figure 20:   The Poisson Distribution, delta = 3.                         38
   Figure 21:   System diagram for Minimoog emulator.                        44
