SMUS — the music score format

SMUS — Simple Musical Score

War in Middle Earth’s music is 22 .smus files in EA IFF 85 “SMUS IFF Simple Musical Score” (Jerry Morrison, Electronic Arts, February 1987) — a published standard, not a bespoke format. Each score references its instruments by name; those are SampledSound .instr files.

Divisions shorter than a 16th note are silently played as rests. That is not a decoder bug and not a data bug — the Sonix player’s own duration table maps 32nd, 64th and 128th notes to $FF, which takes the silence path. A faithful playback engine has to reproduce it.

Container

FORM <size> SMUS
  SHDR  <8 bytes>     score header (required)
  NAME  <variable>    score name (optional)
  INS1  <12+>         instrument reference (zero or more)
  TRAK  <variable>    track event stream (one or more)

SHDR — score header (8 bytes)

+0  u16  tempo     128ths of a quarter note per minute
+2  u8   volume    master volume, 0–127
+3  u8   ctTrack   number of tracks

Divide tempo by 128 for BPM: Aragorn.smus stores 0x397C (14,716) = 115 BPM; Title.smus stores 0x2FA0 (12,192) = 95.25 BPM.

INS1 — instrument reference

+0  u8       register   instrument register index (0, 1, 2 …)
+1  u8       type       instrument type code
+2  u8       data1
+3  u8       data2
+4  varies   name       null-terminated filename stem, e.g. "Piano"

The register field is what TRAK’s instrument-select events refer to; the name field matches a .instr file on disk.

Names can be truncated, and that’s normal. The name field uses chunkSize − 4 bytes; a name longer than the space available is simply cut short — "Bass1Shorter" appears as "Bass1Shor" in Aragorn.smus. Bytes after a null terminator are garbage padding. This is standard SMUS behaviour, not corruption.

TRAK — track event stream

A flat sequence of 2-byte events: a type code, then a data byte.

sID	Event	Data byte means
0–127	Note	The sID itself is the MIDI pitch; data is the duration field below
128	Rest	Duration field below
129	Instrument	Select instrument register
130	Time signature	Bits 7–3 = numerator − 1, bits 2–0 = log2 denominator
131	Key signature	Key signature code
132	Dynamic	Volume / velocity, 0–127
133	MIDI channel	Channel assignment
134	MIDI preset	Program change
135	Clef	Clef type
136	Tempo	Tempo change, quarter notes per minute

The note/rest data byte

 7      6      5-4     3      2-0
+------+------+------+------+------+
| rest | tie  | grp  | dot  | div  |
+------+------+------+------+------+

• rest (bit 7) — silence for the given duration
• tie (bit 6) — the note sustains into the next event
• grp (bits 5–4) — voice group select; when non-zero, Sonix skips the event
• dot (bit 3) — dotted
• div (bits 2–0) — 0 whole, 1 half, 2 quarter, 3 eighth, 4 16th, 5 32nd, 6 64th, 7 128th

Duration in quarter-note units:

base = 4 / (1 << division)
if dot:         base *= 1.5
if triplet:     base *= 2/3
if quintuplet:  base *= 4/5
if septuplet:   base *= 4/7

The Sonix duration table

Confirmed by reading the player’s own lookup table (LAB_01B0 in Sonix.code). Each entry is a CIA tick count at 8 ticks per quarter note — exactly 8× the quarter-note units above:

Index (div)	Division	Value	Quarter notes
0	whole	$20 (32)	4.0
1	half	$10 (16)	2.0
2	quarter	$08 (8)	1.0
3	eighth	$04 (4)	0.5
4	16th	$02 (2)	0.25
5–7	32nd–128th	$FF	rest — unsupported

That last row is the hardware limitation in the callout above: three of the eight encodable divisions have no playable duration on this player at all.

Playback

The reimplementation interprets SMUS directly through a Web Audio renderer rather than pre-converting the scores to another tracker format — the build step now emits only a manifest, and no audio files are generated ahead of time.

Where the full evidence lives

docs/formats/smus.md in the main repository (not part of this site), with WIME’s own playback notes in docs/wime/amiga/music-playback.md and the known decoder issues in docs/wime/amiga/smus-decoder-issues.md.