Amiga Developer CD 2.1/Amiga Developer CD v2.1.iso/Extras/IFF/Old_IFF_Packages/March_1986/iff.text/smus

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"SMUS" IFF Simple Musical Score

Date:    February 5, 1986
From:    Jerry Morrison, Electronic Arts
Status:    Adopted

1. Introduction

This is a reference manual for the data interchange format "SMUS",
which stands for Simple MUsical Score. "EA IFF 85" is Electronic Arts'
standard for interchange format files. A FORM (or "data section")
such as FORM SMUS can be an IFF file or a part of one. [See "EA IFF
85" Electronic Arts Interchange File Format.]

SMUS is a practical data format for uses like moving limited scores
between programs and storing theme songs for game programs. The format
should be geared for easy read-in and playback. So FORM SMUS uses
the compact time encoding of Common Music Notation (half notes, dotted
quarter rests, etc.). The SMUS format should also be structurally
simple. So it has no provisions for fancy notational information needed
by graphical score editors or the more general timing (overlapping
notes, etc.) and continuous data (pitch bends, etc.) needed by
performance-oriented MIDI recorders and sequencers.

A SMUS score can say which "instruments" are supposed play which notes.
But the score is independent of whatever output device and driver
software is used to perform the notes. The score can contain device-
and driver-dependent instrument data, but this is just a cache. As
long as a SMUS file stays in one environment, the embedded instrument
data is very convenient. When you move a SMUS file between programs
or hardware configurations, the contents of this cache usually become
useless.

Like all IFF formats, SMUS is a filed or "archive" format. It is completely
independent of score representations in working memory, editing operations,
user interface, display graphics, computation hardware, and sound
hardware. Like all IFF formats, SMUS is extensible.

SMUS is not an end-all musical score format. Other formats may be
more appropriate for certain uses. (We'd like to design an general-use
IFF score format "GSCR". FORM GSCR would encode fancy notational data
and performance data. There would be a SMUS to/from GSCR converter.)

Section 2 gives important background information. Section 3 details
the SMUS components by defining the required property score header
"SHDR", the optional text properties name "NAME", copyright "(c) ",
and author "AUTH", optional text annotation "ANNO", the optional instrument
specifier "INS1", and the track data chunk "TRAK". Section 4 defines
some chunks for particular programs to store private information.
These are "standard" chunks; specialized chunks for future needs can
be added later. Appendix A is a quick-reference summary. Appendix
B is an example box diagram. Appendix C names the committee responsible
for this standard.

Update: This standard has been revised since the draft versions. The
"INST" chunk type was revised to form the "INS1" chunk type. Also,
several SEvent types and a few text chunk types have been added.

Note: This is a MacWrite[tm] 4.5 document. If you strip it down to a
text file, you'll lose pictures, significant formatting information
like superscripts, and characters like ")". Don't do it.


  ----------------------------------------------------------------
  |(Sorry, EA. We had to strip it down for ease of distribution, |
  |  but we did convert pictures to text-form and where we could |
  |  not do that, we provided ILBM illustrations that people     |
  |  could actually show using the standard "showilbm" program)  |
  ----------------------------------------------------------------


References:

"EA IFF 85" Standard for Interchange Format Files describes the underlying
conventions for all IFF files.

"8SVX" IFF 8-Bit Sampled Voice documents a data format for sampled
instruments.

Electronic Arts[tm] is a trademark of Electronic Arts.

MIDI: Musical Instrument Digital Interface Specification 1.0, International
MIDI Association, 1983.

MacWrite[tm] is a trademark of Apple Computer, Inc.

SSSP: See various articles on Structured Sound Synthesis Project in
Foundations of Computer Music.




2. Background

Here's some background information on score representation in general
and design choices for SMUS.

First, we'll borrow some terminology from the Structured Sound Synthesis
Project. [See the SSSP reference.] A "musical note" is one kind of
scheduled event. It's properties include an event duration, an event
delay, and a timbre object. Theevent duration tells the scheduler
how long the note should last. The event delay tells how long after
starting this note to wait before starting the next event. The timbre
object selects sound driver data for the note; an "instrument" or
"timbre". A "rest" is a sort of a null event. Its only property is
an event delay.

Classical Event Durations

SMUS is geared for "classical" scores, not free-form performances.
So its event durations are classical (whole note, dotted quarter rest,
etc.). It can tie notes together to build a "note event" with an unusual
event duration.

The set of useful classical durations is very small. So SMUS needs
only a handful of bits to encode an event duration. This is very compact.
It's also very easy to display in Common Music Notation (CMN).

Tracks

The events in a SMUS score are grouped into parallel "tracks". Each
track is a linear stream of events.

Why use tracks? Tracks serve 4 functions:

1.    Tracks make it possible to encode event delays very compactly.
A "classical" score has chorded notes and sequential notes; no overlapping
notes. That is, each event begins either simultaneous with or immediately
following the previous event in that track. So each event delay is
either 0 or the same as the event's duration. This binary distinction
requires only one bit of storage.

2.    Tracks represent the "voice tracks" in Common Music Notation.
CMN organizes a score in parallel staves, with one or two "voice tracks"
per staff. So one or two SMUS tracks represents a CMN staff.

3.    Tracks are a good match to available sound hardware. We can
use "instrument settings" in a track to store the timbre assignments
for that track's notes. The instrument setting may change over the
track.

    Furthermore, tracks can help to allocate notes among available
output channels or performance devices or tape recorder "tracks".
Tracks can also help to adapt polyphonic data to monophonic output
channels.

4.    Tracks are a good match to simple sound software. Each track
is a place to hold state settings like "dynamic mark pp ", "time signature
3/4", "mute this track", etc., just as it's a context for instrument
settings. This is a lot like a text stream with running "font" and
"face" properties (attributes). Running state is usually more compact
than, say, storing an instrument setting in every note event. It's
also a useful way to organize "attributes" of notes. With "running
track state" we can define new note attributes in an upward- and
backward-compatible way.

    Running track state can be expanded (run decoded) while loading
a track into memory or while playing the track. The runtime track
state must be reinitialized every time the score is played.

Separated vs. interleaved tracks. Multi-track data could be stored
either as separate event streams or interleaved into one stream. To
interleave the streams, each event has to carry a "track number" attribute.

If we were designing an editable score format, we might interleave
the streams so that nearby events are stored nearby. This helps when
searching the data, especially if you can't fit the entire score into
memory at once. But it takes extra storage for the track numbers and
may take extra work to manipulate the interleaved tracks.

The musical score format FORM SMUS is intended for simple loading
and playback of small scores that fit entirely in main memory. So
we chose to store its tracks separately.

There can be up to 255 tracks in a FORM SMUS. Each track is stored
as a TRAK chunk. The count of tracks (the number of TRAK chunks) is
recorded in the SHDR chunk at the beginning of the FORM SMUS. The
TRAK chunks appear in numerical order 1, 2, 3, .... This is also priority
order, most important track first. A player program that can handle
up to N parallel tracks should read the first N tracks and ignore
any others.

The different tracks in a score may have different lengths. This is
true both of storage length and of playback duration.

Instrument Registers

Instrument reference. In SSSP, each note event points to a "timbre
object" which supplies the "instrument" (the sound driver data) for
that note. FORM SMUS stores these pointers as a "current instrument
setting" for each track. It's just a run encoded version of the same
information. SSSP uses a symbol table to hold all the pointers to
"timbre object". SMUS uses INS1 chunks for the same purpose. They
name the score's instruments.

The actual instrument data to use depends on the playback environment,
but we want the score to be independent of environment. Different
playback environments have different audio output hardware and different
sound driver software. And there are channel allocation issues like
how many output channels there are, which ones are polyphonic, and
which I/O ports they're connected to. If you use MIDI to control the
instruments, you get into issues of what kind of device is listening
to each MIDI channel and what each of its preset sounds like. If you
use computer-based instruments, you need driver-specific data like
waveform tables and oscillator parameters.

We just want to put some orchestration in the score. If the score
wants a "piano", we let the playback program to find a "piano".

Instrument reference by name. A reference from a SMUS score to actual
instrument data is normally by name. The score simply names the instrument,
for instance "tubular bells". It's up to the player program to find
suitable instrument data for its output devices. (More on locating
instruments below.)

Instrument reference by MIDI channel and preset. A SMUS score can
also ask for a specific MIDI channel number and preset number. MIDI
programs may honor these specific requests. But these channel allocations
can become obsolete or the score may be played without MIDI hardware.
In such cases, the player program should fall back to instrument reference
by name.

Instrument reference via instrument register. Each reference from
a SMUS track to an instrument is via an "instrument register". Each
track selects an instrument register which in turn points to the specific
instrument data.

Each score has an array of instrument registers. Each track has a
"current instrument setting", which is simply an index number into
this array. This is like setting a raster image's pixel to a specific
color number (a reference to a color value through a "color register")
or setting a text character to a specific font number (a reference
to a font through a "font register"). This is diagrammed below.


 Track 1  |Set Inst 2| Note | Note | Set Inst 1 | Note | Note | Note |...
        |              |
  +-------------+              |
  |  +------------------------------------+
  |  |           +--------------------------------------------------------+
  |  +-------->|"piano"  ---------------> (internal piano data)         |
  +----------->|"guitar" ---------------> (internal guitar data)    |
           |"Spanish guitar" -------> (internal Spanish guitar data)|
     +-------->|"bass drum" ------------> (internal bass drum data)    |
     |           +--------------------------------------------------------+
     |
     +---------+
           |
 Track 2  |Set Inst 4| Note | Note | Note | Note | Note | Note | Note |...



Locating instrument data by name. "INS1" chunks in a SMUS score name
the instruments to use for that score. The player program uses these
names to locate instrument data.

To locate instrument data, the player performs these steps:

For each instrument register, check for a suitable instrument with
the right name.  "Suitable" means usable with an available output
device and driver.  {Use case independent name comparisons.}

1.    Initialize the instrument register to point to a built-in default
    instrument.  {Every player program must have default instruments.
    Simple programs stop here. For fancier programs, the default
    instruments are a backstop in case the search fails.}

2.    Check any instrument FORMs embedded in the FORM SMUS. (This
    is an "instrument cache".)

3.    Else check the default instruments.

4.    Else search the local "instrument library". (The library might
    simply be a disk directory.)

5.    If all else fails, display the desired instrument name and
    ask the user to pick an available one.

This algorithm can be implemented to varying degrees of fanciness.
It's ok to stop searching after step 1, 2, 3, or 4. If exact instrument
name matches fail, it's ok to try approximate matches. E.g. search
for any kind of "guitar" if you can't find a "Spanish guitar". In
any case, a player only has to search for instruments while loading
a score.

When the embedded instruments are suitable, they save the program
from asking the user to insert the "right" disk in a drive and searching
that disk for the "right" instrument. But it's just a cache. In practice,
we rarely move scores between environments so the cache often works.
When the score is moved, embedded instruments must be discarded (a
cache miss) and other instrument data used.

Be careful to distinguish an instrument's name from its filenameQthe
contents name vs. container name. A musical instrument FORM should
contain a NAME chunk that says what instrument it really is. Its filename,
on the other hand, is a handle used to locate the FORM. Filenames
are affected by external factors like drives, directories, and filename
character and length limits. Instrument names are not.

Issue: Consider instrument naming conventions for consistency. Consider
a naming convention that aids approximate matches. E.g. we could accept
"guitar, bass1" if we didn't find "guitar, bass". Failing that, we
could accept "guitar" or any name starting with "guitar".

Set instrument events. If the player implements the set-instrument
score event, each track can change instrument numbers while playing.
That is, it can switch between the loaded instruments.

Initial instrument settings. Each time a score is played, every tracks'
running state information must be initialized. Specifically, each
track's instrument number should be initialized to its track number.
Track 1 to instrument 1, etc. It's as if each track began with a
set-instrument event.

In this way, programs that don't implement the set-instrument event
still assign an instrument to each track. The INS1 chunks imply these
initial instrument settings.

MIDI Instruments

As mentioned above, A SMUS score can also ask for MIDI instruments.
This is done by putting the MIDI channel and preset numbers in an
INS1 chunk with the instrument name. Some programs will honor these
requests while others will just find instruments by name.

MIDI Recorder and sequencer programs may simply transcribe the MIDI
channel and preset commands in a recording session. For this purpose,
set-MIDI-channel and set-MIDI-preset events can be embedded in a SMUS
score's tracks. Most programs should ignore these events. An editor
program that wants to exchange scores with such programs should recognize
these events. It should let the user change them to the more general
set-instrument events.



3. Standard Data and Property Chunks

A FORM SMUS contains a required property "SHDR" followed by any number
of parallel "track" data chunks "TRAK". Optional property chunks such
as "NAME", copyright "(c) ", and instrument reference "INS1" may also
appear. Any of the properties may be shared over a LIST of FORMs SMUS
by putting them in a PROP SMUS. [See the IFF reference.]

Required Property SHDR

The required property "SHDR" holds an SScoreHeader as defined in these
C declarations and following documentation. An SHDR specifies global
information for the score. It must appear before the TRAKs in a FORM
SMUS.

#define ID_SMUS MakeID('S', 'M', 'U', 'S')
#define ID_SHDR MakeID('S', 'H', 'D', 'R')

typedef struct {
    UWORD tempo;    /* tempo, 128ths quarter note/minute    */
    UBYTE volume;    /* overall playback volume 0 through 127    */
    UBYTE ctTrack;    /* count of tracks in the score    */
    } SScoreHeader;

[Implementation details. In the C struct definitions in this memo,
fields are filed in the order shown. A UBYTE field is packed into
an 8-bit byte. Programs should set all "pad" fields to 0. MakeID is
a C macro defined in the main IFF document and in the source file
IFF.h.]

The field tempo gives the nominal tempo for all tracks in the score.
It is expressed in 128ths of a quarter note per minute, i.e. 1 represents
1 quarter note per 128 minutes while 12800 represents 100 quarter
notes per minute. You may think of this as a fixed point fraction
with a 9-bit integer part and a 7-bit fractional part (to the right
of the point). A course-tempoed program may simply shift tempo right
by 7 bits to get a whole number of quarter notes per minute. The tempo
field can store tempi in the range 0 up to 512. The playback program
may adjust this tempo, perhaps under user control.

Actually, this global tempo could actually be just an initial tempo
if there are any "set tempo" SEvents inside the score (see TRAK, below).
Or the global tempo could be scaled by "scale tempo" SEvents inside
the score. These are potential extensions that can safely be ignored
by current programs. [See More SEvents To Be Defined, below.]

The field volume gives an overall nominal playback volume for all
tracks in the score. The range of volume values 0 through 127 is like
a MIDI key velocity value. The playback program may adjust this volume,
perhaps under direction of a user "volume control".

Actually, this global volume level could be scaled by dynamic-mark
SEvents inside the score (see TRAK, below).

The field ctTrack holds the count of tracks, i.e. the number of TRAK
chunks in the FORM SMUS (see below). This information helps the reader
prepare for the following data.

A playback program will typically load the score and call a driver
routine PlayScore(tracks, tempo, volume), supplying the tempo and
volume from the SHDR chunk.

Optional Text Chunks NAME, (c), AUTH, ANNO

Several text chunks may be included in a FORM SMUS to keep ancillary
information.

The optional property "NAME" names the musical score, for instance
"Fugue in C".

The optional property "(c)J" holds a copyright notice for the score.
The chunk ID "(c)J" serves the function of the copyright characters
")J". E.g. a "(c)J" chunk containing "1986 Electronic Arts" means
") 1986 Electronic Arts".

The optional property "AUTH" holds the name of the score's author.

The chunk types "NAME", "(c) ", and "AUTH" are property chunks. Putting
more than one NAME (or other) property in a FORM is redundant. Just
the last NAME counts. A property should be shorter than 256 characters.
Properties can appear in a PROP SMUS to share them over a LIST of
FORMs SMUS.

The optional data chunk "ANNO" holds any text annotations typed in
by the author.

An ANNO chunk is not a property chunk, so you can put more than one
in a FORM SMUS. You can make ANNO chunks any length up to 231 - 1
characters, but 32767 is a practical limit. Since they're not properties,
ANNO chunks don't belong in a PROP SMUS. That means they can't be
shared over a LIST of FORMs SMUS.

Syntactically, each of these chunks contains an array of 8-bit ASCII
characters in the range R S (SP, hex 20) through R~S (tilde, hex 7F),
just like a standard "TEXT" chunk. [See "Strings, String Chunks, and
String Properties" in "EA IFF 85" Electronic Arts Interchange File
Format.] The chunk's ckSize field holds the count of characters.

#define ID_NAME MakeID('N', 'A', 'M', 'E')
/* NAME chunk contains a CHAR[], the musical score's name.    */

#define ID_Copyright MakeID('(', 'c', ')', ' ')
/* "(c) " chunk contains a CHAR[], the FORM's copyright notice.    */

#define ID_AUTH MakeID('A', 'U', 'T', 'H')
/* AUTH chunk contains a CHAR[], the name of the score's author.    */

#define ID_ANNO MakeID('A', 'N', 'N', 'O')
/* ANNO chunk contains a CHAR[], author's text annotations.    */

Remember to store a 0 pad byte after any odd-length chunk.

Optional Property INS1

The "INS1" chunks in a FORM SMUS identify the instruments to use for
this score. A program can ignore INS1 chunks and stick with its built-in
default instrument assignments. Or it can use them to locate instrument
data. [See "Instrument Registers" in section 2, above.]

#define ID_INS1 MakeID('I', 'N', 'S', '1')

/* Values for the RefInstrument field "type".    */
#define INS1_Name  0    /* just use the name; ignore data1, data2    */
#define INS1_MIDI  1    /* <<data1, data2> = MIDI <<channel, preset>    */

typedef struct {
    UBYTE register;    /* set this instrument register number    */
    UBYTE type;    /* instrument reference type    */
    UBYTE data1, data2;    /* depends on the "type" field    */
    CHAR  name[];    /* instrument name    */
    } RefInstrument;

An INS1 chunk names the instrument for instrument register number
register. The register field can range from 0 through 255. In practice,
most scores will need only a few instrument registers.

The name field gives a text name for the instrument. The string length
can be determined from the ckSize of the INS1 chunk. The string is
simply an array of 8-bit ASCII characters in the range R S (SP, hex
20) through R~S (tilde, hex 7F).

Besides the instrument name, an INS1 chunk has two data numbers to
help locate an instrument. The use of these data numbers is controlled
by the type field. A value type = INS1_Name means just find an instrument
by name. In this case, data1 and data2 should just be set to 0. A
value type = INS1_MIDI means look for an instrument on MIDI channel
# data1, preset # data2. Programs and computers without MIDI outputs
will just ignore the MIDI data. They'll always look for the named
instrument. Other values of the type field are reserved for future
standardization.

See section 2, above, for the algorithm for locating instrument data
by name.

Obsolete Property INST

The chunk type "INST" is obsolete in SMUS. It was revised to form
the "INS1" chunk.

Data Chunk TRAK

The main contents of a score is stored in one or more TRAK chunks
representing parallel "tracks". One TRAK chunk per track.

The contents of a TRAK chunk is an array of 16-bit "events" such as
"note", "rest", and "set instrument". Events are really commands to
a simple scheduler, stored in time order. The tracks can be polyphonic,
that is, they can contain chorded "note" events.

Each event is stored as an "SEvent" record. ("SEvent" means "simple
musical event".) Each SEvent has an 8-bit type field called an "sID"
and 8 bits of type-dependent data. This is like a machine language
instruction with an 8-bit opcode and an 8-bit operand.

This format is extensible since new event types can be defined in
the future. The "note" and "rest" events are the only ones that every
program must understand. We will carefully design any new event types
so that programs can safely skip over unrecognized events in a score.

Caution: SID codes must be allocated by a central clearinghouse to
avoid conflicts.

Here are the C type definitions for TRAK and SEvent and the currently
defined sID values. Afterward are details on each SEvent.

#define ID_TRAK MakeID('T', 'R', 'A', 'K')

/* TRAK chunk contains an SEvent[].    */

/* SEvent: Simple musical event.    */
typedef struct {
    UBYTE sID;    /* SEvent type code    */
    UBYTE data;    /* sID-dependent data    */
    } SEvent;

/* SEvent type codes "sID".        */
#define SID_FirstNote     0
#define SID_LastNote    127    /* sIDs in the range SID_FirstNote through
                  * SID_LastNote (sign bit = 0) are notes. The
                  * sID is the MIDI tone number (pitch).    */
#define SID_Rest        128    /* a rest (same data format as a note).    */

#define SID_Instrument  129    /* set instrument number for this
track.    */
#define SID_TimeSig     130    /* set time signature for this track.    */
#define SID_KeySig      131    /* set key signature for this track.    */
#define SID_Dynamic     132    /* set volume for this track.    */
#define SID_MIDI_Chnl   133    /* set MIDI channel number (sequencers)    */
#define SID_MIDI_Preset 134    /* set MIDI preset number (sequencers)    */

/* SID values 144 through 159: reserved for Instant Music SEvents.    */

/* Remaining sID values up through 254: reserved for future
 * standardization.        */

#define SID_Mark        255    /* sID reserved for an end-mark in RAM.    */

Note and Rest SEvents

The note and rest SEvents SID_FirstNote through SID_Rest have the
following structure overlaid onto the SEvent structure:

typedef struct {
    UBYTE    tone;    /* MIDI tone number 0 to 127; 128 = rest    */
    unsigned chord    :1,    /* 1 = a chorded note    */
        tieOut   :1,    /* 1 = tied to the next note or chord    */
        nTuplet  :2,    /* 0 = none, 1 = triplet, 2 = quintuplet,
    * 3 = septuplet    */
        dot      :1,    /* dotted note; multiply duration by 3/2    */
        division :3;    /* basic note duration is 2-division: 0 = whole
              * note, 1 = half note, 2 = quarter note, I
             * 7 = 128th note    */
    } SNote;

[Implementation details. Unsigned ":n" fields are packed into n bits
in the order shown, most significant bit to least significant bit.
An SNote fits into 16 bits like any other SEvent. Warning: Some compilers
don't implement bit-packed fields properly. E.g. Lattice 68000 C pads
a group of bit fields out to a LONG, which would make SNote take 5-bytes!
In that situation, use the bit-field constants defined below.]

The SNote structure describes one "note" or "rest" in a track. The
field SNote.tone, which is overlaid with the SEvent.sID field, indicates
the MIDI tone number (pitch) in the range 0 through 127. A value of
128 indicates a rest.

The fields nTuplet, dot, and division together give the duration of
the note or rest. The division gives the basic duration: whole note,
half note, etc. The dot indicates if the note or rest is dotted. A
dotted note is 3/2 as long as an undotted note. The value nTuplet
(0 through 3) tells if this note or rest is part of an N-tuplet of
order 1 (normal), 3, 5, or 7; an N-tuplet of order (2J*JnTupletJ+J1).
A triplet note is 2/3 as long as a normal note, while a quintuplet
is 4/5 as long and a septuplet is 6/7 as long.

Putting these three fields together, the duration of the note or rest
is 2-division * {1, 3/2} * {1, 2/3, 4/5, 6/7}

These three fields are contiguous so you can easily convert to your
local duration encoding by using the combined 6 bits as an index into
a mapping table.

The field chord indicates if the note is chorded with the following
note (which is supposed to have the same duration). A group of notes
may be chorded together by setting the chord bit of all but the last
one. (In the terminology of SSSP and GSCR, setting the chord bit to
1 makes the "entry delay" 0.) A monophonic-track player can simply
ignore any SNote event whose chord bit is set, either by discarding
it when reading the track or by skipping it when playing the track.

Programs that create polyphonic tracks are expected to store the most
important note of each chord last, which is the note with the 0 chord
bit. This way, monophonic programs will play the most important note
of the chord. The most important note might be the chord's root note
or its melody note.

If the field tieOut is set, the note is tied to the following note
in the track if the following note has the same pitch. A group of
tied notes is played as a single note whose duration is the sum of
the component durations. Actually, the tie mechanism ties a group
of one or more chorded notes to another group of one or more chorded
notes. Every note in a tied chord should have its tieOut bit set.

Of course, the chord and tieOut fields don't apply to SID_Rest SEvents.

Programs should be robust enough to ignore an unresolved tie, i.e.
a note whose tieOut bit is set but isn't followed by a note of the
same pitch. If that's true, monophonic-track programs can simply ignore
chorded notes even in the presense of ties. That is, tied chords pose
no extra problems.

The following diagram shows some combinations of notes and chords
tied to notes and chords. The text below the staff has a column for
each SNote SEvent to show the pitch, chord bit, and tieOut bit.



        (figure)




If you read the above track into a monophonic-track program, it'll
strip out the chorded notes and ignore unresolved ties. You'll end
up with:



        (figure)




A rest event (sID = SID_Rest) has the same SEvent.data field as a
note. It tells the duration of the rest. The chord and tieOut fields
of rest events are ignored.

Within a TRAK chunk, note and rest events appear in time order.

Instead of the bit-packed structure SNote, it might be easier to assemble
data values by or-ing constants and to disassemble them by masking
and shifting. In that case, use the following definitions.

#define noteChord  (1<<<<7)    /* note is chorded to next note    */

#define noteTieOut (1<<<<6)    /* tied to next note/chord    */

#define noteNShift 4    /* shift count for nTuplet field    */
#define noteN3     (1<<<<noteNShift)    /* note is a triplet    */
#define noteN5     (2<<<<noteNShift)    /* note is a quintuplet    */
#define noteN7     (3<<<<noteNShift)    /* note is a septuplet    */
#define noteNMask  noteN7    /* bit mask for the nTuplet field    */

#define noteDot    (1<<<<3)    /* note is dotted    */

#define noteD1     0    /* whole note division    */
#define noteD2     1    /* half note division    */
#define noteD4     2    /* quarter note division    */
#define noteD8     3     /* eighth note division    */
#define noteD16    4     /* sixteenth note division    */
#define noteD32    5     /* thirty-secondth note division    */
#define noteD64    6     /* sixty-fourth note division    */
#define noteD128   7     /* 1/128 note division    */
#define noteDMask  noteD128    /* bit mask for the division field    */

#define noteDurMask 0x3F    /* mask for combined duration fields    */

Note: The remaining SEvent types are optional. A writer program doesn't
have to generate them. A reader program can safely ignore them.

Set Instrument SEvent

One of the running state variables of every track is an instrument
number. An instrument number is the array index of an "instrument
register", which in turn points to an instrument. (See "Instrument
Registers", in section 2.) This is like a color number in a bitmap;
a reference to a color through a "color register".

The initial setting for each track's instrument number is the track
number. Track 1 is set to instrument 1, etc. Each time the score is
played, every track's instrument number should be reset to the track
number.

The SEvent SID_Instrument changes the instrument number for a track,
that is, which instrument plays the following notes. Its SEvent.data
field is an instrument register number in the range 0 through 255.
If a program doesn't implement the SID_Instrument event, each track
is fixed to one instrument.

Set Time Signature SEvent

The SEvent SID_TimeSig sets the time signature for the track. A "time
signature" SEvent has the following structure overlaid on the SEvent
structure:

typedef struct {
    UBYTE    type;    /* = SID_TimeSig    */
    unsigned timeNSig :5,    /* time sig. "numerator" is timeNSig + 1 */
    timeDSig :3;    /* time sig. "denominator" is 2timeDSig:
             * 0 = whole note, 1 = half note, 2 = quarter
             * note, I 7 = 128th note    */
    } STimeSig;

[Implementation details. Unsigned ":n" fields are packed into n bits
in the order shown, most significant bit to least significant bit.
An STimeSig fits into 16 bits like any other SEvent. Warning: Some
compilers don't implement bit-packed fields properly. E.g. Lattice
C pads a group of bit fields out to a LONG, which would make an STimeSig
take 5-bytes! In that situation, use the bit-field constants defined
below.]

The field type contains the value SID_TimeSig, indicating that this
SEvent is a "time signature" event. The field timeNSig indicates the
time signature "numerator" is timeNSig + 1, that is, 1 through 32
beats per measure. The field timeDSig indicates the time signature
"denominator" is 2timeDSig, that is each "beat" is a 2-timeDSig note
(see SNote division, above). So 4/4 time is expressed as timeNSig
= 3, timeDSig = 2.

The default time signature is 4/4 time.

Beware that the time signature has no effect on the score's playback.
Tempo is uniformly expressed in quarter notes per minute, independent
of time signature. (Quarter notes per minute equals beats per minute
only if timeDSig = 2, n/4 time). Nonetheless, any program that has
time signatures should put them at the beginning of each TRAK when
creating a FORM SMUS because music editors need them.

Instead of the bit-packed structure STimeSig, it might be easier to
assemble data values by or-ing constants and to disassemble them by
masking and shifting. In that case, use the following definitions.

#define timeNMask  0xF8    /* bit mask for the timeNSig field    */
#define timeNShift 3    /* shift count for  timeNSig field    */

#define timeDMask  0x07    /* bit mask for the timeDSig field    */

Key Signature SEvent

An SEvent SID_KeySig sets the key signature for the track. Its data
field is a UBYTE number encoding a major key:

data    key    music notation    data    key    music notation
J0    C maj
J1    G    #    J8    F    b
J2    D    ##    J9    Bb    bb
J3    A    ###    10    Eb    bbb
J4    E    ####    11    Ab    bbbb
J5    B    #####    12    Db    bbbbb
J6    F#    ######    13    Gb    bbbbbb
J7    C#    #######    14    Cb    bbbbbbb

A SID_KeySig SEvent changes the key for the following notes in that
track. C major is the default key in every track before the first
SID_KeySig SEvent.

Dynamic Mark SEvent

An SEvent SID_Dynamic represents a dynamic mark like ppp and fff in
Common Music Notation. Its data field is a MIDI key velocity number
0 through 127. This sets a "volume control" for following notes in
the track. This "track volume control" is scaled by the overall score
volume in the SHDR chunk.

The default dynamic level is 127 (full volume).

Set MIDI Channel SEvent

The SEvent SID_MIDI_Chnl is for recorder programs to record the set-MIDI-channe
l low level event. The data byte contains a MIDI channel number. Other
programs should use instrument registers instead.

Set MIDI Preset SEvent

The SEvent SID_MIDI_Preset is for recorder programs to record the
set-MIDI-preset low level event. The data byte contains a MIDI preset
number. Other programs should use instrument registers instead.

Instant Music Private SEvents

Sixteen SEvents are used for private data for the Instant Music program.
SID values 144 through 159 are reserved for this purpose. Other programs
should skip over these SEvents.

End-Mark SEvent

The SEvent type SID_Mark is reserved for an end marker in working
memory. This event is never stored in a file. It may be useful if
you decide to use the filed TRAK format intact in working memory.

More SEvents To Be Defined

More SEvents can be defined in the future. The sID codes 133 through
143 and 160 through 254 are reserved for future needs. Caution: sID
codes must be allocated by a central "clearinghouse" to avoid conflicts.
When this SMUS standard passes the "draft" state, Commodore-Amiga
will be in charge of this activity.

The following SEvent types are under consideration and should not
yet be used.

Issue: A "change tempo" SEvent changes tempo during a score. Changing
the tempo affects all tracks, not just the track containing the change
tempo event.

One possibility is a "scale tempo" SEvent SID_ScaleTempo that rescales
the global tempo:
currentTempo := globalTempo * (data + 1) / 128

This can scale the global tempo (in the SHDR) anywhere from x1/128
to x2 in roughly 1% increments.

An alternative is two events SID_SetHTempo and SID_SetLTempo. SID_SetHTempo
gives the high byte and SID_SetLTempo gives the low byte of a new
tempo setting, in 128ths quarter note/minute. SetHTempo automatically
sets the low byte to 0, so the SetLTempo event isn't needed for course
settings. In this scheme, the SHDR's tempo is simply a starting tempo.

An advantage of SID_ScaleTempo is that the playback program can just
alter the global tempo to adjust the overall performance time and
still easily implement tempo variations during the score. But the
"set tempo" SEvent may be simpler to generate.

Issue: The events SID_BeginRepeat and SID_EndRepeat define a repeat
span for one track. The span of events between a BeginRepeat and an
EndRepeat is played twice. The SEvent.data field in the BeginRepeat
event could give an iteration count,1 through 255 times or 0 for "repeat
forever".

Repeat spans can be nested. All repeat spans automatically end at
the end of the track.

An event SID_Ending begins a section like "first ending" or "second
ending". The SEvent.data field gives the ending number. This SID_Ending
event only applies to the innermost repeat group. (Consider generalizing
it.)

A more general alternative is a "subtrack" or "subscore" event. A
"subtrack" event is essentially a "subroutine call" to another series
of SEvents. This is a nice way to encode all the possible variations
of repeats, first endings, codas, and such.

To define a subtrack, we must demark its start and end. One possibility
is to define a relative brach-to-subtrack event SID_BSR and a return-from-subtr
ack event SID_RTS. The 8-bit data field in the SID_BSR event can reach
as far as 512 SEvents. A second possibility is to call a subtrack
by index number, with an IFF chunk outside the TRAK defining the start
and end of all subtracks. This is very general since a portion of
one subtrack can be used as another subtrack. It also models the tape
recording practice of first "laying down a track" and then selecting
portions of it to play and repeat. To embody the music theory idea
of playing a sequence like "ABBA", just compose the "main" track entirely
of subtrack events. A third possibility is to use a numbered subtrack
chunk "STRK" for each subroutine.




4. Private Chunks

As in any IFF FORM, there can be private chunks in a FORM SMUS that
are designed for one particular program to store its private information.
All IFF reader programs skip over unrecognized chunks, so the presense
of private chunks can't hurt.

Instant Music stores some global score information in a chunk of ID
"IRev".



Appendix A. Quick Reference

Type Definitions

Here's a collection of the C type definitions in this memo. In the
"struct" type definitions, fields are filed in the order shown. A
UBYTE field is packed into an 8-bit byte. Programs should set all
"pad" fields to 0.

#define ID_SMUS MakeID('S', 'M', 'U', 'S')
#define ID_SHDR MakeID('S', 'H', 'D', 'R')

typedef struct {
    UWORD tempo;    /* tempo, 128ths quarter note/minute    */
    UBYTE volume;    /* overall playback volume 0 through 127    */
    UBYTE ctTrack;    /* count of tracks in the score    */
    } SScoreHeader;

#define ID_NAME MakeID('N', 'A', 'M', 'E')
/* NAME chunk contains a CHAR[], the musical score's name.    */

#define ID_Copyright MakeID('(', 'c', ')', ' ')
/* "(c) " chunk contains a CHAR[], the FORM's copyright notice.    */

#define ID_AUTH MakeID('A', 'U', 'T', 'H')
/* AUTH chunk contains a CHAR[], the name of the score's author.    */

#define ID_ANNO MakeID('A', 'N', 'N', 'O')
/* ANNO chunk contains a CHAR[], author's text annotations.    */

#define ID_INS1 MakeID('I', 'N', 'S', '1')

/* Values for the RefInstrument field "type".    */
#define INS1_Name 0    /* just use the name; ignore data1, data2    */
#define INS1_MIDI 1    /* <<data1, data2> = MIDI <<channel, preset>    */

typedef struct {
    UBYTE register;    /* set this instrument register number    */
    UBYTE type;    /* instrument reference type    */
    UBYTE data1, data2;    /* depends on the "type" field    */
    CHAR  name[];    /* instrument name    */
    } RefInstrument;

#define ID_TRAK MakeID('T', 'R', 'A', 'K')
/* TRAK chunk contains an SEvent[].    */

/* SEvent: Simple musical event.    */
typedef struct {
    UBYTE sID;    /* SEvent type code    */
    UBYTE data;    /* sID-dependent data    */
    } SEvent;

/* SEvent type codes "sID".        */
#define SID_FirstNote     0
#define SID_LastNote    127    /* sIDs in the range SID_FirstNote through
                  * SID_LastNote (sign bit = 0) are notes. The
                 * sID is the MIDI tone number (pitch).    */
#define SID_Rest        128    /* a rest (same data format as a note).    */

#define SID_Instrument  129    /* set instrument number for this
track.    */
#define SID_TimeSig     130    /* set time signature for this track.    */
#define SID_KeySig      131    /* set key signature for this track.    */
#define SID_Dynamic     132    /* set volume for this track.    */
#define SID_MIDI_Chnl   133    /* set MIDI channel number (sequencers)    */
#define SID_MIDI_Preset 134    /* set MIDI preset number (sequencers)    */

/* SID values 144 through 159: reserved for Instant Music SEvents.    */

/* Remaining sID values up through 254: reserved for future
 * standardization.        */

#define SID_Mark        255    /* sID reserved for an end-mark in RAM.    */

/* SID_FirstNote..SID_LastNote, SID_Rest SEvents    */
typedef struct {
    UBYTE    tone;    /* MIDI tone number 0 to 127; 128 = rest    */
    unsigned chord    :1,    /* 1 = a chorded note    */
        tieOut   :1,    /* 1 = tied to the next note or chord    */
        nTuplet  :2,    /* 0 = none, 1 = triplet, 2 = quintuplet,
             * 3 = septuplet    */
        dot      :1,    /* dotted note; multiply duration by 3/2    */
        division :3;    /* basic note duration is 2-division: 0 = whole
                * note, 1 = half note, 2 = quarter note, I
             * 7 = 128th note    */
    } SNote;

#define noteChord  (1<<<<7)    /* note is chorded to next note    */

#define noteTieOut (1<<<<6)    /* tied to next note/chord    */

#define noteNShift 4    /* shift count for nTuplet field    */
#define noteN3     (1<<<<noteNShift)    /* note is a triplet    */
#define noteN5     (2<<<<noteNShift)    /* note is a quintuplet    */
#define noteN7     (3<<<<noteNShift)    /* note is a septuplet    */
#define noteNMask  noteN7    /* bit mask for the nTuplet field    */

#define noteDot    (1<<<<3)    /* note is dotted    */

#define noteD1     0    /* whole note division    */
#define noteD2     1    /* half note division    */
#define noteD4     2    /* quarter note division    */
#define noteD8     3     /* eighth note division    */
#define noteD16    4     /* sixteenth note division    */
#define noteD32    5     /* thirty-secondth note division    */
#define noteD64    6     /* sixty-fourth note division    */
#define noteD128   7     /* 1/128 note division    */
#define noteDMask  noteD128    /* bit mask for the division field    */

#define noteDurMask 0x3F    /* mask for combined duration fields    */

/* SID_Instrument SEvent        */
/* "data" value is an instrument register number 0 through 255.    */

/* SID_TimeSig SEvent        */
typedef struct {
    UBYTE    type;    /* = SID_TimeSig    */
    unsigned timeNSig :5,    /* time sig. "numerator" is timeNSig + 1 */
        timeDSig :3;    /* time sig. "denominator" is 2timeDSig:
               * 0 = whole note, 1 = half note, 2 = quarter
             * note, I 7 = 128th note    */
    } STimeSig;

#define timeNMask  0xF8    /* bit mask for the timeNSig field    */
#define timeNShift 3    /* shift count for  timeNSig field    */

#define timeDMask  0x07    /* bit mask for the timeDSig field    */

/* SID_KeySig SEvent        */
/* "data" value 0 = Cmaj; 1 through 7 = G,D,A,E,B,F#,C#;
 * 8 through 14 = F,Bb,Eb,Ab,Db,Gb,Cb.    */

/* SID_Dynamic SEvent        */
/* "data" value is a MIDI key velocity 0..127.    */

SMUS Regular Expression

Here's a regular expression summary of the FORM SMUS syntax. This
could be an IFF file or part of one.

SMUS    ::= "FORM" #{    "SMUS" SHDR [NAME] [Copyright] [AUTH] [IRev]
        ANNO* INS1*  TRAK*  InstrForm* }

SHDR    ::= "SHDR" #{    SScoreHeader    }
NAME    ::= "NAME" #{    CHAR*    } [0]
Copyright    ::= "(c) " #{    CHAR*    } [0]
AUTH    ::= "AUTH" #{    CHAR*    } [0]
IRev    ::= "IRev" #{    ...    }

ANNO    ::= "ANNO" #{    CHAR*    } [0]
INS1    ::= "INS1" #{    RefInstrument    } [0]

TRAK    ::= "TRAK" #{    SEvent*    }

InstrForm    ::= "FORM" #{    ...    }

The token "#" represents a ckSize LONG count of the following {braced}
data bytes. Literal items are shown in "quotes", [square bracket items]
are optional, and "*" means 0 or more replications. A sometimes-needed
pad byte is shown as "[0]".

Actually, the order of chunks in a FORM SMUS is not as strict as this
regular expression indicates. The SHDR, NAME, Copyright, AUTH, IRev,
ANNO, and INS1 chunks may appear in any order, as long as they precede
the TRAK chunks.

The chunk RInstrFormS represents any kind of instrument data FORM
embedded in the FORM SMUS. For example, see the document "8SVX" IFF
8-Bit Sampled Voice. Of course, a recipient program will ignore an
instrument FORM if it doesn't recognize that FORM type.



Appendix B. SMUS Example

Here's a box diagram for a simple example, a SMUS with two instruments
and two tracks. Each track contains 1 note event and 1 rest event.



     +-----------------------------------------+    ------
     |'FORM'        94               |        ^
     |    +-----------------------------------+  |      |
     |  |'SMUS'                    |  |        |
     |  +-----------------------------------+  |      |
     |    | +-------------------------------+ |  |      |
     |    | | 'SHDR'    4          | |  |        |
     |    | | 12800, 127, 2          | |  |      |
     |    | +-------------------------------+ |  |      |
     |    | +-------------------------------+ |  |      |
     |    | | 'NAME'    10              | |  |        |
     |    | | 'Fugue in C'          | |  |      |
     |    | +-------------------------------+ |  |      |
     |    | +-------------------------------+ |  |
     |    | | 'INS1'    9              | |  |      (94 bytes)
     |    | | 1,0,0,0,'piano'          | |  |
     |    | +-------------------------------+ |  |      |
     |    | 0                    |  |      |
     |    | +-------------------------------+ |  |      |
     |    | | 'INS1'    10              | |  |        |
     |    | | 2,0,0,0,'guitar'          | |  |      |
     |    | +-------------------------------+ |  |      |
     |    | +-------------------------------+ |  |      |
     |    | | 'TRAK'    4              | |  |        |
     |    | | 60, 16, 128, 16          | |  |      |
     |    | +-------------------------------+ |  |      |
     |    | +-------------------------------+ |  |      |
     |    | | 'TRAK'    4              | |  |       |
     |    | | 128, 16, 60, 16          | |  |      |
     |    | +-------------------------------+ |  |      |
     |    +-----------------------------------+  |      V
     +-----------------------------------------+    -----



Appendix B. Standards Committee

The following people contributed to the design of this IFF standard:

Bob "Kodiak" Burns, Commodore-Amiga
R. J. Mical, Commodore-Amiga
Jerry Morrison, Electronic Arts
Greg Riker, Electronic Arts
Steve Shaw, Electronic Arts
Barry Walsh, Commodore-Amiga




















The "0" after the first INS1 chunk is a pad byte.



Appendix C. Standards Committee

The following people contributed to the design of this SMUS standard:

Ralph Bellafatto, Cherry Lane Technologies
Geoff Brown, Uhuru Sound Software
Steve Hayes, Electronic Arts
Jerry Morrison, Electronic Arts