From The MPEG-4 Structured Audio Book by John Lazzaro and John Wawrzynek.

Part V/3: The Slib Library

Sections

Library Opcodes

tan   sinh   cosh   tanh   asinh   acosh   atanh  

Commonly-Used Constants

PI   CPS_MIDDLEC   NONE   MIDI_SCALE  

Introduction

Good libraries make the process of writing software easier. It also makes the job of maintaining completed programs easier, especially when the maintainer is not the original author.

Slib is a SAOL library, distributed with sfront, that provides low-level support utilities to the SAOL programmer. The primary goal of Slib is to replace hard-coded constants and repetitive code fragments with easy-to-understand symbols and opcodes.

 

Using Slib

The remaining sections of this chapter describe Slib features. The right panel of each section begins with the include statement that should be placed at the top of a SAOL file that uses the feature.

For example, to use Slib's trigonometric functions in a program, add:

#include <Slib/trig.hs>

to the top of the program file. For this method to work, sfront needs to be properly configured to see its library directory, as described on the right panel.

Sfront Library Paths

Sfront currently pre-processes SAOL 
and SASL source files before parsing
them, if the platform has gcc 
available. To do so, use the:

sfront -gcc -cpp

options. In addition sfront needs to 
know the absolute path of the 
sfront/lib directory. This can be 
done via the command line using 
the -Is option; for example, for
my own setup:

sfront -gcc -cpp -Is /opt/sfront/lib

Alternatively, you can set the 
environment variable 
SFRONT_INCLUDE_PATH to the string
/opt/sfront/lib. 

By default, sfront searches the
/usr/lib/sfront directory, which
is where the Debian and Redhat
package distributions put Slib.

See this part of the sfront reference
manual for more information about
using the pre-processor.

Trigonometric Opcodes

The SAOL core opcode library includes these trigonometric functions:

opcode sin(xsig x)
opcode cos(xsig x)
opcode acos(xsig x)
opcode asin(xsig x)
opcode atan(xsig x)

Slib provides additional user-defined opcodes for trigonometry using the same calling conventions, as shown on the right panel.

#include <Slib/trig.hs>

opcode tan(xsig x)    

   Tangent of x.

opcode sinh(xsig x)

   Hyperbolic sine of x.

opcode cosh(xsig x)

   Hyperbolic cosine of x.

opcode tanh(xsig x)   

   Hyperbolic tangent of x.

opcode asinh(xsig x)

   Inverse hyperbolic sine of x.

opcode acosh(xsig x)

   Inverse hyperbolic cosine of x.

opcode atanh(xsig x)

   Inverse hyperbolic tangent of x.

Numeric Constants

A typical SAOL program has many literal constants. Some of these constants are from classical mathematics, like pi and e, while others are musical constants. Manually entering these constants introduces inaccuracy and error into computations.

Slib contains symbol definitions for many constants of this type, which we describe in this section. These symbols may be used just like SAOL variable names in expressions. We show these symbols in related groups on the right panel.

 

Symbols for Euler's constant and for Pi are shown on the right panel.

Math Constants
--------------

#include <Slib/std.hs>

M_PI and PI

  Pi (3.141...)

M_E

  e (Euler's constant, 2.71 ...)

SAOL tempo computations are often done relative to the default tempo value of 60 beats per second. The right panel shows constants related to this value.

Use these constants in conjunction with the tempo core opcodes.

Tempo constants
---------------

#include <Slib/std.hs>

INIT_TEMPO

  Initial tempo for MP4-SA 
  (60 beats/second).

INIT_INVTEMPO     

  1/INIT_TEMPO (1/60 seconds/beat)


The s_rate and k_rate standard names are constants that describe the audio and control sampling rates of the SAOL program. Since these values are set by global parmeters, the standard names are constants.

Programs often derive a set of secondary execution cycle constants from s_rate and k_rate. The right panel shows symbol definitions for common derived quantities.

Next section.

Temporal Constants
------------------

#include <Slib/std.hs>

ACYCLE      

   Number of a-passes in an execution
   cycle [int(s_rate/k_rate)].

ARATE       

   Audio sample rate [s_rate Hz].

ATIME       

   Audio sampling period 
   [1/s_rate seconds].

KRATE       

   Control sampling rate [k_rate Hz].

KTIME

   Control sampling period 
   [1/k_rate seconds].

SRATE       

   Audio sample rate [s_rate Hz].

STIME

   Audio sample period 
   [1/s_rate seconds].

SAOL supports four pitch representations via a set of 12 conversion opcodes.

Slib provides Middle C and Concert A constants for these representations, and macros for creating arbitrary constant values in these formats. Macros use the same syntax as opcode calls in expressions, but have no rate semantics issues. This example shows a legal uses of the pitch macro in SAOL code:

instr ptest () {

ksig k;
asig a;

k = kphasor(CPS_SEMITONES(7));
a = aphasor(CPS_SEMITONES(0));

}
Pitch Constants and Macros
--------------------------

#include <Slib/std.hs>

CPS_MIDDLEC      
CPS_CONCERTA 

  Middle C (261.6256 Hz) and
  Concert A (440 Hz) in
  cps notation. 
     
MIDI_MIDDLEC
MIDI_CONCERTA 

  Middle C (note number 60) 
  and Concert A (note number
  69) in MIDI notation.

PCH_MIDDLEC      
PCH_CONCERTA 

  Middle C (8) and Concert A 
  (8.9) in pch notation.

OCT_MIDDLEC      
OCT_CONCERTA 

  Middle C (8) and Concert A 
  (8.75) in oct notation.

CPS_SEMITONES(x)
MIDI_SEMITONES(x)
PCH_SEMITONES(x)
OCT_SEMITONES(x)

  These macros take a parameter, 
  the number of semitones away 
  from Middle C, and compute the
  cps, MIDI, pch, or oct value.
  Semitones may be a positive or
  negative integral value. The
  constant OCTAVESTEPS, the 
  number of semitones per octave
  (12), is provided for use with
  these macros.

Coding Constants

Many core opcodes, core wavetables, and SAOL and SASL language elements use special integer constants to specify special behaviors.

The most common constant value of this sort is -1, used to code indefinite duration in SAOL and SASL instr statements, indefinite size in wavetable generators, and in many other contexts.

This convention can make SAOL programs difficult to read -- in each case, the programmer needs to remember that the constant isn't playing a numeric role in the program, but rather a symbolic one.


The right panel shows a set of symbol definitions to use instead of integers in these situation. The NONE symbol is defined to replace -1 in programs, to improve readability, much like the NULL constant improves readability in C programs.

The NONE Constant
-----------------

#include <Slib/std.hs>

NONE as a value of -1, and should
be used in the following contexts:


* For the size parameter in
  wavetable generators, to indicate
  that the generator should compute 
  the size of the table.

* For the duration parameter in SAOL
  and SASL instr statements, to 
  indicate indefinite duration.

* The loops parameter in the oscil and
  koscil core opcodes.

* The nharm parameter in the buzz core
  opcode and core wavetable generator.

The fracdelay core opcode has a method parameter, which takes on integral values to code different delay line modes. The right panel shows a set of symbolic constants to use for the method parameter.

Next section.

fracdelay() Constants
---------------------

#include <Slib/std.hs>

aopcode fracdelay(ksig method, 
                  xsig p1, xsig p2) 

This core opcode, which is 
usually used via a sequence
of oparray calls, has different
semantics based on the value
of the method parameter. Use
these symbols for the method
parameter:


 FRAC_INIT (1)

   Initializes delay line 
   structure. p1 is the length
   of the delay, in seconds.
   Returns 0.

 FRAC_TAP (2)

   Returns data from the 
   delay line. p1 is the
   position to read, in seconds.
   If p1 does not correspond
   to an integral delay line
   position, return value is
   interpolated.

 FRAC_SET (3)

   Sets the delay line position 
   p1 to value p2. p1 is 
   truncated to an integral delay
   line position. Returns 0.

 FRAC_SUM (4)

   Sums the value p2 into 
   delay line position p1. p1
   is truncated to an integral 
   delay line position. Returns 
   new value of delay line 
   position that is updated.

 FRAC_SHIFT (5)

   Shifts delay line by 1. Shifts
   a zero into the delay line,
   returns value shifted off the
   end of the delay line.


The random core wavetable generator has a dist parameter, which takes on integral values to code different random number distributions. The right panel shows a set of symbolic constants to use for the method parameter.

Next section.

random wavetable generator
--------------------------

#include <Slib/std.hs>

table t(random, size, 
        dist, p1 [,p2])

This core wavetable generator 
creates a table of length size
filled with random numbers. 
The distribution of the random
numbers depends on the integral
value of the dist parameter. 
Use these symbols for the dist
parameter:

 RANDOM_UNIFORM (1)

  Uniform distribution over
  [p1, p2].

 RANDOM_LINEAR (2)

  Linearly ramped distribution
  from p1 to p2.

 RANDOM_EXPON (3)

  Poisson distribution, 
  p(x) =  p1*exp(-p1*x).

 RANDOM_GAUSSIAN (4)

  Gaussian distribution,
  mean p1 and variance p2

 RANDOM_PROCESS (5)

  Table holds a binary 
  sequence (0.0 and 1.0) that
  is generated by a Poisson
  process specified by the 
  formula  p(x) =  p1*exp(-p1*x)

The window core wavetable generator has a type parameter, which takes on integral values to code different window shapes. The right panel shows a set of symbolic constants to use for the type parameter.

Next section.

window wavetable generator
--------------------------

#include <Slib/std.hs>

table t(window, size, type [,p])

This core wavetable generator 
creates a table of length size
holding a windowing function. 
The type of window function 
created depends on the integral
value of the type parameter. The
constants in this section are
the supported windows.


 WINDOW_HAMMING (1)

   Hamming.

 WINDOW_HANNING (2)

   Hanning (raise cosine)

 WINDOW_BARTLETT (3) 

   Bartlett (triangular)

 WINDOW_GAUSSIAN (4)

   Gaussian

 WINDOW_KAISER (5)

   Kaiser, with parameter p

 WINDOW_BOXCAR (6)

   Boxcar

The SSM Library

The MIDI standard names MIDIctrl[128], MIDIbend, and MIDItouch provide raw access to controller, pitch bend, and aftertouch values in MIDI contexts.

The SSM library provides access to these standard names at a higher level of abstraction. As shown on the right panel, this library is loaded by including the Slib/ssm.hs file.

The SSM library is a set of symbols, such as SSMmodwheel, that use the functional name of MIDI controller channels. These k-rate symbols can be used like MIDI standard names in expressions.

Each SSM name has several features:

  1. The value of the name is scaled to be in the range [0,1], [-1,1], or a binary 0/1 value, depending on the type of controller.
  2. By default, only the most-significant byte of two-byte controllers are used. If the symbol SSM_HIGHRES is defined before including Slib/ssm.hs, both the LSB and MSB bytes are used.
  3. Non-binary controllers as smoothed at the k-rate, using the port command. By default, the half-time of this smoothing is 4/k_rate. To use a different smoothing rate, define the symbol SSM_SMOOTHRATE to the smoothing time, in seconds, before including Slib/ssm.hs.
  4. Each smoothed scaled symbol name, such as SSMmodwheel, has a companion unsmoothed scaled symbol name starting with SM (i.e. SMmodwheel).

Next section.

The SSM Library
---------------

See left panel for optional
symbols SSM_SMOOTHRATE
and SSM_HIGHRES.

#include <Slib/ssm.hs>


SSMattack

 Range: [0,1]
 Name: Sound Attack
 Uses: MIDIctrl[73]

SSMbalance

 Range: [-1,+1]
 Name: Stereo Balance
 Uses: MIDIctrl[8,40]

SSMbend

 Range: [-1,+1]
 Name: Pitch Bend Wheel
 Uses: MIDIbend

SSMbreath

 Range: [0,1]
 Name: Breath Controller
 Uses: MIDIctrl[2,34]

SSMbright

 Range: [0,1]
 Name: Sound Brightness
 Uses: MIDIctrl[74]

SSMbutton1 

 Range: 0/1
 Name: G.P Button 1
 Uses: MIDIctrl[80]

SSMbutton2

 Range: 0/1
 Name: G.P Button 2
 Uses: MIDIctrl[81]

SSMbutton3

 Range: 0/1
 Name: G.P Button 3
 Uses: MIDIctrl[82]

SSMbutton4

 Range: 0/1
 Name: G.P Button 4
 Uses: MIDIctrl[83]

SSMchorus

 Range: [0,1]
 Name: Chorus Level
 Uses: MIDIctrl[93]

SSMdataslider

 Range: [0,1]
 Name: Data Entry Slider
 Uses: MIDIctrl[6, 38]

SSMdetune

 Range: [0,1]
 Name: Detuning Amount
 Uses: MIDIctrl[94]

SSMeffect

 Range: [0,1]
 Name: Effects Level
 Uses: MIDIctrl[91]

SSMeffect1

 Range: [0,1]
 Name: Effect Control 1
 Uses: MIDIctrl[12,44]

SSMeffect2

 Range: [0,1]
 Name: Effect Control 2
 Uses: MIDIctrl[13,45]

SSMexpress

 Range: [0,1]
 Name: Expression
 Uses: MIDIctrl[11,43]

SSMfoot

 Range: [0,1]
 Name: Foot Controller
 Uses: MIDIctrl[2, 34]

SSMhold

 Range: 0/1
 Name: Hold Pedal
 Uses: MIDIctrl[64]

SSMhold2

 Range: 0/1
 Name: Hold 2 Pedal
 Uses: MIDIctrl[69]

SSMlegato 

 Range: 0/1
 Name: Legato Pedal
 Uses: MIDIctrl[68]


SSMlocal          

  Range: 0/1
  Name: Local Kbd Off/On
  Uses: MIDIctrl[122]

SSMmodwheel

  Range: [0,1]
  Name: Modulation Wheel
  Uses: MIDIctrl[1, 33]   

SSMpan

  Range: [-1,+1]
  Name: Stereo Panning
  Uses: MIDIctrl[10,42]

SSMphasor

  Range: [0,1]
  Name: Phasor Level
  Uses: MIDIctrl[95]

SSMporta

  Range: 0/1
  Name: Portamento On/Off
  Uses: MIDIctrl[65]

SSMportatime

  Range: [0,1]
  Name: Portamento Time
  Uses: MIDIctrl[5, 36]

SSMrelease

  Range: [0,1]
  Name: Sound Release
  Uses: MIDIctrl[72]

SSMslider1

  Range: [0,1]
  Name: G. P. Slider 1
  Uses: MIDIctrl[16]

SSMslider2

  Range: [0,1]
  Name: G. P. Slider 2
  Uses: MIDIctrl[17]

SSMslider3

  Range: [0,1]
  Name: G. P. Slider 3
  Uses: MIDIctrl[18]

SSMslider4

  Range: [0,1]
  Name: G. P. Slider 4
  Uses: MIDIctrl[19]

SSMsoft

  Range: 0/1
  Name: Soft Pedal
  Uses: MIDIctrl[67]

SSMsound6

  Range: [0,1]
  Name: Sound Control 6
  Uses: MIDIctrl[75]

SSMsound7

  Range: [0,1]
  Name: Sound Control 7
  Uses: MIDIctrl[76]

SSMsound8

  Range: [0,1]
  Name: Sound Control 8
  Uses: MIDIctrl[77]

SSMsound9

  Range: [0,1]
  Name: Sound Control 9
  Uses: MIDIctrl[78]

SSMsound10

  Range: [0,1]
  Name: Sound Control 10
  Uses: MIDIctrl[79]

SSMsust

  Range: 0/1
  Name: Sustenuto Pedal
  Uses: MIDIctrl[66]

SSMtimbre

  Range: [0,1]
  Name: Sound Timbre
  Uses: MIDIctrl[71]

SSMtouch

  Range: [0,1]
  Name: Aftertouch
  Uses: MIDItouch

SSMtremelo

  Range: [0,1]
  Name: Tremelo Level
  Uses: MIDIctrl[92]

SSMvar

  Range: [0,1]
  Name: Sound Variation
  Uses: MIDIctrl[70]

SSMvolume

  Range: [0,1]
  Name: Channel Volume
  Uses: MIDIctrl[7, 39]

Note that decoder support
is needed to handle Registered
and Non-Registered Parameters,
since these are event-based.
So, no definitions for Data
Entry Button +/- and Parameter
Number controllers appear above.
Data Entry Slider is included,
since its possible to use these
values in a non-event-based way.

MIDI Constants

The SSM library may not be appropriate for all MIDI applications. The right panel shows a set of constants for scaling MIDI data at a lower level of abstraction.

Next section.

MIDI number scaling
-------------------

#include <Slib/std.hs>

The constants in this section
are for computing on the (7-bit)
velocity and note-number values,
and for creating alternatives 
to the SSM library.


MIDI_MAX      

  Largest value for 7-bit
  MIDI numbers. (127) 

MIDI_SCALE    

  To scale 7-bit MIDI
  into [0, 1]. (1/127)

MIDI_NULL        

  The zero value for
  bipolar 7-bit MIDI.
  (64)

MIDI_SSCALE

  Use with MIDI_NULL
  for [-1, 1] scaling.
  (1/64)

MIDI_BIGMAX   

  Largest value for
  14-bit MIDI numbers,      
  used by MIDIbend, and
  coded by two MIDIctrl[]
  entries by some 
  controllers. (16383)

MIDI_BIGSCALE  

  To scale 14-bit MIDI
  into [0, 1] (1/16383).

MIDI_BIGNULL   

  The zero value for 
  bipolar 14-bit MIDI.
  (8192)

MIDI_BIGSSCALE 

  Use with MIDI_BIGNULL 
  for [-1, 1] scaling. 
  (1/8192)

MIDI_MSBSHIFT  

  Multiply MSB's of
  MIDIctrl[] by this
  value, and add to LSB
  to get 14-bit MIDI.
  (128).

MIDI_OFF 

  For binary 7-bit 
  MIDIctrl[] entries.
  Values greater than
  MIDI_OFF are 1, else 0.
  (63)

General MIDI Presets

The General MIDI specification assigns preset numbers to particular types of instrument timbres. It also defines a percussion map.

The gmidi.hs library contains symbolic definitions for these presets. Several sample definitions are shown on the right panel; see the library file for the complete list.

General MIDI presets
--------------------

#include <Slib/gmidi.hs>


Sample presets:

Defined name        #   Description

GM_ACOUSTICGRAND    0   Acoustic Grand
GM_BRIGHTACOUSTIC   1   Brite Acoustic
GM_ELECTRICGRAND    2   Electr. Grand

                  [...]

GM_APPLAUSE       126   Applause
GM_GUNSHOT        127   Gunshot



Sample note numbers:

Definition            #   Description

GMD_ACOUSTICBASSDRUM  35  Ac Bass Drum
GMD_BASSDRUM1         36  Bass Drum 1
GMD_SIDESTICK         37  Side Stick
                    
                     [...]

GMD_MUTETRIANGLE      80  Mute Triangle
GMD_OPENTRIANGLE      81  Open Triangle

Summary

Part V/2 completes the main text of the MPEG 4 Structured Audio Book. We conclude the text with the Appendix, that includes a keyword index.

Appendix A: Aspects of MP4-SA Not Covered In this Book

 


Copyright 2000 John Lazzaro and John Wawrzynek.