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<TITLE>The MP4-SA Book: Part III/2: MIDI Instrument Control</TITLE>
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<META name="description" content="MIDI Control of SAOL Instruments. 
Describes how to use a MIDI file or real-time MIDI stream to 
instantiate SAOL instruments. Describes standard names for MIDI.">
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<A HREF="../../../index.html">mp4-sa</A>-><A HREF="../../index.html">
the mp4-sa book</A>-><A HREF="../index.html">
instrument control</A>-><STRONG>with MIDI</STRONG>
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<H3>From <A HREF="../../index.html">The MPEG-4 Structured Audio Book</A>
by <A HREF="http://www.cs.berkeley.edu/~lazzaro/index.html">
John Lazzaro</A> and <A HREF="http://www.cs.berkeley.edu/~johnw">
John Wawrzynek.</A></H3>

<H1>Part III/2: MIDI Instrument Control</H1>


<TABLE WIDTH="100%" CELLPADDING=12 CELLSPACING=0>
<TR>
<TD WIDTH="70%" VALIGN=top BGCOLOR="#CCFFCC">

<H2>Sections</H2>
<UL>
<LI>
<B><A HREF="#intro">Introduction</A>.</B>
<LI>
<B><A HREF="#basic">MIDI Basics</A>.</B> Overview of MIDI commands.
<LI>
<B><A HREF="#saol">MIDI Files and SAOL</A>.</B> Trigger times and channels.
<LI>
<B><A HREF="#instr">SAOL Instruments for MIDI</A>.</B> Specializations.
<LI>
<B><A HREF="#stnames">Standard Names</A>.</B> Access the MIDI data stream.
<LI>
<B><A HREF="#stream">Streaming and MIDI</A>.</B> MIDI commands without trigger times.

</UL>


</TD>
<TD WIDTH="70%" VALIGN=top BGCOLOR="#CCFFCC">
<H2>Standard Names:</H2>

<B>
<P>
<A HREF="#stnames">MIDIctrl</A> 
<A HREF="#stnames">MIDItouch</A> 
<A HREF="#stnames">MIDIbend</A> 
<A HREF="#stnames">channel</A> 
<A HREF="#stnames">preset</A> 
</B>

<H2>Language Elements:</H2>

<B>
<P>
<A HREF="#instr">preset</A> 
</B>

</TD>
</TR>
</TABLE>


<TABLE WIDTH="100%" CELLPADDING=12 CELLSPACING=0>
<TR>

<TD WIDTH="50%" VALIGN=top BGCOLOR="#CCFFCC">
<H2><A NAME="intro">Introduction</A></H2>

<P>
MIDI (Musical Instrument Digital Interface) is the dominant score
language in electronic music.  Most electronic musical instruments
have network ports that communicate MIDI commands, or have USB
ports that may be used for MIDI transport.  

<P>
MIDI ports may be added to most personal computers, using an
inexpensive adaptor (for MIDI sent over a USB cable, an adaptor is not
needed).  Most musical software applications use the MIDI File Format,
a score language based on MIDI.

<P>
MP4-SA supports the MIDI File Format as an alternative score language
to SASL. MP4-SA also supports the inclusion of streaming MIDI commands
in an MP4 bitstream.

<P>
In this chapter, we give a basic introduction to MIDI, and show how
SAOL programs interact with MIDI commands.

</TD>

<TD WIDTH="50%" VALIGN=top BGCOLOR="#FFCCCC">

<pre> </pre>

</TD>

</TR>
</TABLE>


<TABLE WIDTH="100%" CELLPADDING=12 CELLSPACING=0>
<TR>

<TD WIDTH="50%" VALIGN=top BGCOLOR="#CCFFCC">
<H2><A NAME="basic">MIDI Basics</A></H2>

<P>
In this section, we describe MIDI commands and MIDI Files, focusing on
features relevant to MP4-SA. 

<P>
MIDI was originally designed to let musicians use a single electronic
piano keyboard to play notes on several different electronic musical
instruments.

<P>
In a typical architecture, the piano keyboard sends out control
information, in the form of MIDI commands, on a "MIDI Out" network
port (a 5-pin DIN connector). This port is wired to the "MIDI In" port
of one of the instruments. This instrument regenerates the data on a
"MIDI Through" jack, that is connected to another instrument.

<P>
In this way, several instruments are daisy-chained together, each
listening to the same stream of MIDI commands. Most MIDI commands
include a <I>channel number</I> field (an integer between 0 and
15). In a typical installation, each instrument is programmed to only
respond to commands that have a specific MIDI channel number.

<H4>MIDI Commands</H4>

<P>
See the right panel for the syntax of the MIDI commands discussed in
this section. Although these commands are defined as binary objects,
in this chapter we discuss MIDI using a symbolic notation.

<P>
The MIDI commands for starting (<B>NoteOn</B>) and ending
(<B>NoteOff</B>) sounds are defined using the vocabulary of the piano
keyboard. These commands specify a key number (an integer between 0
and 127, with 60 being Middle C), the velocity that the note was
pressed or released, and a channel number. 

<P>
Electronic keyboards often have pressure sensors underneath the
keyboard that generate an additional control signal while a note is
depressed. Some keyboards have a single sensor for the entire
keyboard, while others have a dedicated sensor for each note. 

<P>
The MIDI commands <B>Touch</B> and <B>CTouch</B> send information
about the current pressure under a single key or the entire keyboard,
respectively.

<P>
Many electronic keyboards also have a wheel on the left side of
the keyboard, with a center detent. Moving the wheel off the
center detent acts to smoothly bend the pitch of all depressed
notes. The <B>PWheel</B> command sends the current value
of the pitch wheel.

<P>
Electronic musical instruments typically have the ability to 
play many different types of sounds. MIDI refers to these 
sound types as presets, numbered between 0 and 127. The
MIDI <B>PChange</B> command instructs an instrument on 
a particular channel to switch to a particular preset.

<P>
In addition to pitch wheels, electronic piano keyboards often have
other attached controllers, such as pedals, secondary wheels, etc.
The <B>CChange</B> command lets a keyboard send the value of a
controller on a specific MIDI channel.

<P>
The controller in the CChange command is specified as a number
between 0-127, with many numbers linked to specific devices (for
example, the piano sustain pedal is controller 64). Other controller 
numbers are used to extend other MIDI commands. For example, controller
32 extends the PChange command, by specifying the bank of 
128 presets that the PChange command accesses.

<H4>MIDI Files</H4>

<P>
As MIDI ports became available for personal computers, sequencer
software became available for recording MIDI data from
electronic piano keyboards and assembling the data fragments
into a complete performance.

<P>
The MIDI File Format became the standard way to transfer performances
between different sequencer packages. The MIDI File Format adds
trigger times to the MIDI commands described in the last section.
MIDI Files support trigger times with units of beats, with tempo
commands to map between beats and seconds.

<P>
The simplest MIDI File type, Format 0, stores all note data in a
single track, which consists of a list of MIDI commands with time
triggers. This format limits the performance to use 16 MIDI channels.

<P>
Format 1 MIDI files store note data on multiple tracks, with each
track having a distinct 16 MIDI channels available. This format
supports an arbitrary number of channels.


</TD>

<TD WIDTH="50%" VALIGN=top BGCOLOR="#FFCCCC">

<H2>MIDI Command Syntax</H2>

<TT>
<pre>

<B>NoteOn</B> Ch Note Velocity


Ch: 0-15. The channel that should
play the note.

Note: 0-127. The piano keyboard
note to play. 60 is middle C.

Velocity: 0-127. How hard the 
the piano keyboard note was struct.



<B>NoteOff</B> Ch Note Velocity


Ch: 0-15. The channel that should
terminate the note.

Note: 0-127. The piano keyboard
note to terminate.

Velocity: 0-127. How quickly the
piano keyboard note was lifted.



<B>Touch</B> Ch Note Value


Ch: 0-15. The channel sent
the pressure information. 

Note: 0-127. The piano keyboard
note that receives the pressure.

Value: 0-127. The pressure value.



<B>CTouch</B> Ch Value


Ch: 0-15. The channel sent
the pressure information.

Value: 0-127. The pressure value.



<B>PWheel</B> Ch Value


Ch: 0-15. The channel sent
the pitch wheel information. 

Value: 0-16383. Pitch wheel
value. Center detent is 8192.



<B>PChange</B> Ch Preset


Ch: 0-15. The channel sent
the preset change.

Preset: 0-127. The new preset
number to use.



<B>CChange</B> Ch Ctrl Value


Ch: 0-15. The channel sent
the controller change.

Ctrl: 0-127. The controller
to change.

Value: 0-127. The new value
for the controller.

</pre>
</TT>

<H2>MIDI File Commands</H2>

<TT>
<pre>

<B>tempo</B> value

Translate trigger time values
(in units of beats) to absolute
time (in units of seconds).

</pre>
</TT>

</TD>

</TR>
</TABLE>


<TABLE WIDTH="100%" CELLPADDING=12 CELLSPACING=0>
<TR>

<TD WIDTH="50%" VALIGN=top BGCOLOR="#CCFFCC">
<H2><A NAME="saol">MIDI Files and SAOL</A></H2>

<P>
In this section, we describe the MP4-SA semantics of MIDI File scores.
MP4-SA supports MIDI File Format 0 and 1.

<H4>Triggering Commands</H4>

<P>
MP4-SA supports MIDI File scores with trigger times in units of
beats. Absolute trigger times (units of seconds) are not supported.

<P>
A MIDI File command executes when the trigger time is less than or
equal to the current clock time of the SAOL simulation.  The trigger
time is converted from beats to seconds, using the current value of
SAOL global tempo.

<P>
As described in the last section, a MIDI File may include <B>tempo</B>
commands.  When a MIDI <B>tempo</B> commands executes, it changes the
value of the SAOL global tempo. If a MIDI File does not include a
tempo command at time zero, the SAOL global tempo takes on an initial
value of 120 beats per minute (the MIDI File default).

<P>
In Part III/3, we present a <A
HREF="../saolc/index.html#order">table</A> that shows the place that
MIDI commands trigger in the execution cycle.

<H4>Channel Numbers</H4>

<P>
As shown in the last section, most MIDI commands include a channel
number. For Format 1 MIDI files, these commands may appear on 
different tracks, each of which has a separate "channel space".

<P>
SAOL considers a MIDI command with channel number <TT>N</TT> that
appears on track <TT>M</TT> of a MIDI Format 1 File to have
the <I>extended channel number</I>  <TT>16*M + N</TT>. Tracks
in a MIDI File are numbered in order of appearance in the file,
starting with 0.

<P>
For a Format 0 MIDI file, the channel number of a MIDI command is
also the extended channel number of the command.

</TD>

<TD WIDTH="50%" VALIGN=top BGCOLOR="#FFCCCC">
<pre> </pre>
</TD>

</TR>
</TABLE>


<TABLE WIDTH="100%" CELLPADDING=12 CELLSPACING=0>
<TR>

<TD WIDTH="50%" VALIGN=top BGCOLOR="#CCFFCC">
<H2><A NAME="instr">SAOL Instruments for MIDI</A></H2>

<P>
A MIDI <B>NoteOn</B> command creates a new instance of SAOL
instrument.  SAOL instruments that are accessible by MIDI commands use
a special declaration header, as shown on the right panel.

<P>
MIDI-capable SAOL instruments have two instrument parameters. The
first parameter is initialized with the note number specified by the
instantiating NoteOn command. The second parameter is
initialized with the velocity value of the NoteOn command.

<P>
MIDI-capable SAOL instruments have the keyword <B>preset</B> following
the parameter list, followed by a list of one or more MIDI preset
numbers (separated by spaces). MIDI preset numbers are integers
starting from zero. A particular present number may only be used by
one instrument.

<P>
A NoteOn command creates an instance of the instrument that has
the same preset number as the extended channel of the command.  

<P>
Before the first NoteOn command executes on a MIDI channel, a
<B>PChange</B> command should execute to set the preset number for the
channel.

<P>
If the MIDI channel requires a preset number greater than 127, the
PChange command should be preceded by a <B>CChange</B> command
for controller 32, to select a preset bank number.

<P>
An instance created on a specific channel to play a specific note
executes until a <B>NoteOff</B> executes with that that channel/note
combination. At that time, the instrument is scheduled for termination
at the end of the current execution cycle. Termination may be delayed
in the following ways:

<OL>
<LI>
<B>Sustain Pedal.</B> If the sustain pedal on the extended channel is
depressed (i.e. MIDI controller 64 has a non-zero value) the
termination for the instance is delayed until the sustain pedal is
released (i.e. MIDI controller 64 is zero).  Note that MIDI controller
64 is initialized to zero at the start of the simulation, and is
changed by a CChange command.
<LI><B>SAOL Intervention.</B> As described in Part III/3, the SAOL
<A HREF="../saolc/index.html#extend">extend</A> statement
may be used to delay the termination of an instrument instance. 
Instruments may use this technique to implement
the release phase of the amplitude envelope of a note.
</OL>


</TD>

<TD WIDTH="50%" VALIGN=top BGCOLOR="#FFCCCC">

<H2>Example MIDI Headers</H2>

<TT>
<pre>

instr piano(note, vel) preset 13 2 {}
instr sax(num, v) preset 300 {}

</pre>
</TT>

<H2>Example MIDI Instrument</H2>

<TT>
<pre>

// tutorial sine wave
// for MIDI 

instr mtone (num, vel) preset 0 { 

  ivar a;     // freq const
  ivar scale; //  amp const
  asig x, y;  //  osc state
  asig init;  //  init flag

  // **********************
  // computed during i-pass
  // **********************

  // turns MIDI number into 
  // oscillator constant 

  a = 2*sin(3.1415927*
	    cpsmidi(num)/s_rate);

  // volume for tone

  scale = min(vel/127, 1);

  // **********************
  // computed during a-pass
  // **********************

  if (init == 0)
    {
      x = 0.25;
      init = 1;
    }

  x = x - a*y;
  y = y + a*x;
  
  output(y*scale);

}
</pre>
</TT>
</TD>

</TR>
</TABLE>


<TABLE WIDTH="100%" CELLPADDING=12 CELLSPACING=0>
<TR>

<TD WIDTH="50%" VALIGN=top BGCOLOR="#CCFFCC">
<H2><A NAME="stnames">Standard Names</A></H2>

<P>
Five standard names contain information about MIDI: 
<B>channel</B>, <B>preset</B>, <B>MIDIbend</B>, 
<B>MIDItouch</B>, and <B>MIDIctrl</B>.

<P>
The i-rate <B>channel</B> holds the extended channel number of the
NoteOn command that created the instance, while the i-rate
<B>preset</B> standard name holds the preset value of this extended
channel.

<P>
The k-rate <B>MIDIbend</B> standard name holds the value of the last
PWheel command targeted to the extended channel of the
instrument. If no PWheel commands have targeted this channel,
<B>MIDIbend</B> has the value 8192 (associated with the center detent
of the pitch wheel).

<P>
The value of the k-rate <B>MIDItouch</B> standard name is updated
whenever a CTouch command executes that targets the extended
channel associated with the instance, or a Touch command
executes that targets the note number <I>and</I> the extended channel
number of the instance. 

<P>
The <B>MIDIctrl</B> array standard name holds the latest values of the
128 MIDI controllers. The array index chooses the controller number.  A
CChange command targeting the extended channel associated with
the instance updates these controller values. 

<P>
Most MIDIctrl values are initialized to zero at the start of
program execution; see the right panel for exceptions. Also,
the <B>MIDIctrl</B> standard name may be used as an <I>lval</I> in
a SAOL <A HREF="../../saol/exstat/index.html#assign">assignment</A>
statement. 

<H4>Non-MIDI Instances</H4>

<P>
A SAOL program under MIDI control may have instrument instances that
are not created by MIDI commands. These instances may be be created by
SASL <A HREF="../sasl/index.html#instr">instr</A> lines, or may be <A
HREF="../../saol/bus/index.html#effects">effects</A>
instruments created by global <B>send</B> statements.

<P>
If a SASL or effects instance uses a MIDI standard name, the returned
values reflect the status of the <I>MIDI master channel</I>. The right
panel describes how MP4-SA determines the MIDI master channel.

<P>
In addition, as we learn in the following chapter, instruments may be
dynamically created in a SAOL program, using the <A
HREF="../saolc/index.html#instr">instr</A> statement.  Accesses to 
MIDI standard names in a dynamic instrument reflect the MIDI channel of
its parent instrument.

</TD>

<TD WIDTH="50%" VALIGN=top BGCOLOR="#FFCCCC">

<H2>MIDI Standard Names</H2>

<TT>
<PRE>
ivar channel;
ivar preset;
ksig MIDIbend;
ksig MIDItouch;
ksig MIDIctrl[128];


The <A HREF="../../special/slib/index.html">Slib</A> library provides <A HREF="../../special/slib/index.html#ssm">access</A>
to normalized and smoothed 
versions of the MIDI standard
names.

Slib also includes constants for 
scaling <A HREF="../../special/slib/index.html#midic">MIDI data</A>, and preset maps
for <A HREF="../../special/slib/index.html#gmidi">General MIDI</A>. 

</PRE>
</TT>

<H2>MIDIctrl Default Values</H2>

<TT>
<PRE>
(only non-zero values shown)

Number      Function      Value
7           Volume         100
10          Pan             64
11          Expression     127

</PRE>
</TT>

<H2>The MIDI Master Channel</H2>

<TT>
<PRE>
[1] If a real-time control
source is present, extended
channel 0 is the MIDI master
channel. Else,

[2] If streaming MIDI is
encoded in the MP4-SA file,
the first channel is the MIDI
master channel. Else,

[3] If a MIDI File is present
in the MP4-SA file, the first
track with MIDI commands is the
MIDI Master Channel.

</PRE>
</TT>

</TD>
</TR>
</TABLE>


<TABLE WIDTH="100%" CELLPADDING=12 CELLSPACING=0>
<TR>

<TD WIDTH="50%" VALIGN=top BGCOLOR="#CCFFCC">
<H2><A NAME="stream">Streaming and MIDI</A></H2>

<P>
In the previous sections, we describe how a MIDI File may control a
SAOL program. An MP4-SA binary encoding of this system would include
the binary MIDI File data at the start of the MP4-SA file.

<P>
The MP4-SA file format also supports distributing individual MIDI
commands throughout the file, that do not have individual trigger
times.  These commands execute at the next opportunity for executing
MIDI commands in the <A HREF="../saolc/index.html#order">execution
order</A>, using the MIDI command semantics described in the
previous sections of this chapter.

<P>
Note that this distributed MIDI encoding is identical to to the data
encoding on a MIDI port of an electronic keyboard. As a result, SAOL
decoders may support real-time interactions with a MIDI keyboard using
the framework described in this chapter. The <TT>sfront</TT> decoder
includes an interface of this nature.

<P>
<B>Next:</B>
<A HREF="../saolc/index.html">Part III/3: SAOL Instrument Control</A></H2>

</TD>

<TD WIDTH="50%" VALIGN=top BGCOLOR="#FFCCCC">

<pre> </pre>

</TD>

</TR>
</TABLE>



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<A HREF="../../../copyright/index.html">Copyright 1999 John Lazzaro and John
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