CDFM Format

Format type	Music
Notation type	Custom
Instruments	OPL, PCM
Max channel count	13
Max track count	1
Max pattern count	128
Max order count	256
Tags?	None
Games	Zone 66

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CDFM Format (alternatively: 670 Format) was developed by the demogroup Renaissance for their Amnesia demo, and was later used in their game Zone 66. It consists of either nine Adlib channels (for Adlib hardware), nine OPL and four PCM channels (for Sound Blaster hardware) or patches to be played as MIDI instruments (for GUS hardware.)

In Zone 66, most songs have hardware-specific versions, even where the SB song could drop the PCM channels and be played on Adlib. In these cases the PCM drum channels have been replaced with OPL instruments.

File format

The file begins with a header. Those fields marked [GUS only] are missing entirely in SoundBlaster/AdLib songs, and those fields marked [AdLib/SB only] are missing entirely in the GUS variant of the song format.

Data type	Name	Description
UINT32LE	sampleOffset	[GUS only] Offset of instrument samples from start of file
BYTE	tempo	[Adlib/SB only] Playback speed, larger is slower [GUS only] Unknown, always 0x66, changing has no effect
BYTE	patternListSize	Size of pattern list
BYTE	numPatterns	Number of patterns in song
BYTE	numDigInst	Number of PCM or GUS instruments in song
BYTE	numOPLInst	[Adlib/SB only] Number of OPL instruments in song
BYTE	loopDest	Index into `patternOrder` for next pattern to play after the final one when looping the song
UINT32LE	sampleOffset	[Adlib/SB only] Offset of instrument samples from start of file
UINT8[patternListSize]	patternOrder	Order of patterns in the song, `patternListSize` bytes in length
UINT32LE[numPatterns]	patternOffset	Offset of each pattern's data, relative to the start of the pattern data
PCM_INST[numDigInst]	pcmInst	[Adlib/SB only] 16 bytes of info for each digital (PCM) instrument
OPL_INST[numOPLInst]	oplInst	[Adlib/SB only] 11-byte instrument patch for each FM (OPL) instrument
GUS_INST[numDigInst]	gusInst	[GUS only] 11 bytes of info for each GUS patch

The pattern data immediately follows. The patternOffset values are relative to this position, so a value of 0x00000000 corresponds to the first byte here.

PCM_INST is:

Data type	Name	Description
UINT32LE	address_ptr	Used to place address of sample start in memory - ignore when reading, write as 0x00000000
UINT32LE	length	Length of sample, in bytes
UINT32LE	loopStart	Offset of loop return, in bytes, relative to start of sample
UINT32LE	loopEnd	Offset of loop trigger, in bytes, relative to start of sample. Use 0x00FFFFFF for no loop.

The PCM instruments begin at sampleOffset and are raw (no header) 8-bit unsigned PCM data. If the sample loops, as soon as playback reaches loopEnd (which could be before the end of the sample), playback will immediately jump to loopStart. The middle-C frequency for all PCM instruments is fixed at 8287 Hz (ProTracker standard).

OPL_INST is:

Data type	Name	OPL base register	Description
UINT8	iFeedback	0xC0	Feedback/connection
UINT8	iModChar	0x20	Modulator characteristic (Mult, KSR, EG, VIB and AM flags)
UINT8	iModScale	0x40	Modulator key scaling/output level
UINT8	iModAttack	0x60	Modulator attack/decay level
UINT8	iModSustain	0x80	Modulator sustain/release level
UINT8	iModWaveSel	0xE0	Modulator wave select
UINT8	iCarChar	0x23	Carrier characteristic (Mult, KSR, EG, VIB and AM flags)
UINT8	iCarScale	0x43	Carrier key scaling/output level
UINT8	iCarAttack	0x63	Carrier attack/decay level
UINT8	iCarSustain	0x83	Carrier sustain/release level
UINT8	iCarWaveSel	0xE3	Carrier wave select

The OPL base registers in this list are for the two operators controlling the first OPL channel. Adjust them accordingly for the relevant OPL channel.

GUS_INST is:

Data type	Name	Description
UINT8	flags	Bitfield: 1=! Makes pitch higher, 2=loop, 16=! unknown - mutes instrument
UINT16LE	rate	Playback sampling rate for pitch to be middle-C
UINT32LE	loopStart	Sample offset, in bytes, of loop start
UINT32LE	length	Length of sample, in bytes

All sample data is 8-bit signed. If the loop bit is set (i.e. flags & 2) then when the end of the sample is reached playback jumps immediately to the byte offset indicated by loopStart.

Tempo

All songs use the standard module speed/tempo system. The tempo is fixed at 144, and the speed can be changed per song. For SB/AdLib songs, the speed is set once with the value obtained from the file header, while GUS songs include a 'set speed' command at the start of each pattern.

Pattern data (SB/AdLib)

The musical score data for SoundBlaster/AdLib files consists of a sequence of variable-length commands, in the following format:

0x00-0x0C: Play note

Command	Byte 2	Byte 3
0x00	`jfffnnnn`	`iiiivvvv`

Play a note on the given channel.

The command byte is 0x00 through 0x0C. The value controls the channel used for the note:
- 0x00: digital 1
- 0x03: digital 4
- 0x04: FM 1
- 0x0C: FM 9
- 0x0D-0x0F: Invalid
j: High (fifth) bit of instrument number.
fff: The octave of the note to play. Middle-C is within octave 2 for digital channels (they have 4 octaves). FM channels have 7 octaves, and the middle-C is in octave 4.
nnnn: The number of the note to play within the octave (0-11).
iiii: The lower four bits of the instrument to use. A value of zero uses the first instrument. This is the first PCM instrument on a digital channel, and the first OPL instrument on an FM channel.
vvvv: Note volume/velocity. 0x0 is almost silent, 0xF is full volume. Notes can be played with zero velocity and then faded in with subsequent volume change commands. Volume is linear for both digital and FM channels, which needs to be translated for FM channels (the OPL chip has a logarithmic volume curve).

Note that for FM channels, the channel number modulo 4 is added to the resulting FNUM OPL parameter. This causes the note to be slightly detuned, which is used in the Zone 66 soundtrack to fatten some sounds by playing them on two neighbouring FM channels.

0x20-0x2C: Set volume

Command	Byte 2
0x20	`0000vvvv`

Set the volume of the playing note on the given channel.

The command byte is 0x20 through 0x2C, with the lower four bits representing the channel number as with playing a note.
vvvv: Note volume/velocity. 0x0 is silent, 0xF is full volume.

0x40: Delay

Command	Byte 2
0x40	`tttttttt`

Delay for the given number of ticks before continuing with the next event.

tttttttt: Number of ticks to wait

0x60: End of pattern

Command
0x60

This must be the last command in each pattern. Playback will jump to the next pattern in the sequence specified in the song header.

0x80: Unknown

This command is not used in any known files and crashes Zone 66. Its purpose, or perhaps incomplete intended purpose, is unknown.

Pattern data (GUS)

The musical score data for GUS files also consists of a sequence of variable-length commands, however the commands are different from the ones used in SB/AdLib files. The commands are in the following format:

0x00: Delay

Command	Byte 2
0x01	`tttttttt`

Delay for the given number of ticks before continuing with the next event.

tttttttt: Number of ticks to wait

0x01: Set speed

Command	Byte 2
0x01	`ssssssss`

Adjust the song playback speed.

ssssssss: New speed. This is the same as the 'speed' in standard .mod files (i.e. the number of frames per row), with the module tempo fixed at 144.

0x02: End of pattern

Command
0x02

This must be the last command in each pattern. Playback will jump to the next pattern in the sequence specified in the song header.

0x40-0x4F: Play note

Command	Byte 2	Byte 3	Byte 4
0x00	`ffffffff`	`ppppvvvv`	`iiiiiiii`

Play a note on the given channel.

The command byte is always 0x40 through 0x4F. The value controls the channel used for the note:
- 0x00: GUS channel 1
- 0x01: GUS channel 2
- 0x0F: GUS channel 16 ! Assumed, please confirm
ffffffff: Note. Add 25 to this value (i.e. transpose up by two octaves and one note) to obtain standard MIDI note numbers.
pppp: Panning, 0=centre, 1=full right, 15=full left
vvvv: Velocity, logarithmic, 0=silent, 1=1%, 2=4%, 3=7% ... 12=49.8%, 13=60%, 14=74.9%, 15=100%
iiiiiiii: Instrument, 0=first, 1=second, etc.

0x80-0x8F: Set volume

Command	Byte 2
0x80	`ppppvvvv`