Doom WAD MUS music

The music of the Doom engine games is in MUS, the DMX sound library’s own format: a compact form of MIDI with one stream of events for all channels. Doom’s songs are the lumps named D_ and the map, such as D_E1M1; Heretic’s start MUS_. Numbers are little-endian.

Header

Offset	Size	Type	Name	Description
0	4	ASCII	id	`MUS` and the byte `1A`.
4	2	u16	score length	The bytes of the score.
6	2	u16	score start	Where the score starts, from the start of the lump.
8	2	u16	primary channels	The number of channels the song uses, not counting percussion.
10	2	u16	secondary channels	Channels beyond those; usually 0.
12	2	u16	instrument count	The number of instrument numbers that follow.
14	2	u16	reserved	0.
16	2 each	u16	instruments	The instruments the song uses, for the game to load before it plays: General MIDI programs 0 to 127, and 135 to 181 for percussion notes 35 to 81.

The score usually starts straight after the instrument list, at 16 + 2 × the instrument count.

Events

Each event starts with a descriptor byte, then its data, then, when bit 7 of the descriptor is set, a delay before the next event.

Bits of the descriptor	Meaning
0 to 3	The channel, 0 to 15; 15 is percussion
4 to 6	The event, below
7	Last: a delay follows

Event	Name	Data
0	Release note	The note, 0 to 127.
1	Play note	The note in bits 0 to 6; bit 7 set when a second byte follows with the volume, 0 to 127. Without it, the channel’s last volume is used.
2	Pitch bend	One byte, 0 to 255; 128 is no bend.
3	System event	One byte, a controller from 10 to 14, below.
4	Change controller	Two bytes: the controller, below, and its value.
5	End of measure	None.
6	End of score	None. The song loops back to its start if the game says so.
7	Not used

The delay is a count of ticks of 1/140 of a second, written 7 bits a byte, highest bits first, with bit 7 set on every byte but the last.

Controller	Meaning	MIDI
0	Instrument	Program change
1	Bank select	Controller 0
2	Modulation	1
3	Volume	7
4	Pan	10
5	Expression	11
6	Reverb depth	91
7	Chorus depth	93
8	Sustain pedal	64
9	Soft pedal	67
10	All sounds off	120
11	All notes off	123
12	Mono	126
13	Poly	127
14	Reset all controllers	121

0Change controller 40 00 1E: channel 0, instrument 303 bytes
3Play note 90 BC 64 46: channel 0, note 60 at volume 100, then wait 70 ticks4 bytes
7Release note 00 3C: channel 0, note 602 bytes
9End of score 601 byte

An invented score: half a second of middle C

As a MIDI file

A MUS score maps closely onto a standard MIDI file of one track. The explorer converts it the way Chocolate Doom’s converter does: 70 ticks to a quarter note at 120 beats a minute, which is 140 ticks a second; MUS channel 15 becomes MIDI channel 10, and the other channels take MIDI channels in the order they are first used, passing over channel 10; the pitch bend is multiplied by 64; and the controllers become the MIDI controllers in the table. The MIDI file opens as a file of its own, and the explorer shows the song’s notes and plays them.

.WAD File Format – MUS music

Header

Events

As a MIDI file