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

# Part V/3: The Slib Library

## Sections

- Introduction.
- Using Slib. Accessing a library feature in a program.
- Trigonometric Opcodes. Additions to the core opcode library.
- Numeric Constants. Useful constants for audio programming.
- Coding Constants. Mnenomics for opcode/wavetable codes.
- The SSM Library. High-level access to MIDI standard names.
- MIDI Constants. Useful constants for MIDI programming.
- General MIDI Presets. General MIDI preset and drum-map constants.

## 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.