MDX File Format

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MDX is a binary MML format, compiled from plaintext MXDRV MML. It is specific to MXDRV for the X68000.

MDX files consist of a header, a list of instrument voices, and the MML commands.

Header format

  • Title in Shift_JIS encoding, followed by 0x0d 0x0a 0x1a
  • PDX file name, followed by 0x00 (just 0x00 if there is no PDX file)
  • Word: Voice data offset
  • 9 or 16 Words: MML data offset

The voice and MML offsets are relative to the voice data offset value's position (right after the title and PDX file name). To implement this in code, just use a ftell() after you've read the PDX file name. The MML data offset array points to each of the channels. Some files use 9 channels, others use 16. To detect which one it is, two methods exist:

  • subtract the file position of the first MML data offset word from its value, then divide by 2. See MDX.h for the implementation.
  • as in mxd2063.lzh / SRC/MDX2MUS.ASM (search for `#EX-PCM`), take the first byte of the first MML channel, and set channels to 16 if it is E8h.

The FM channels are labeled A through H. The PCM channel is labeled P. The extra channels, when the Mercury expansion card is present, are labeled Q through W.

Voice format

This corresponds to the registers in the YM2151 sound chip. Each field is 1 byte. The x4 fields are 4 bytes corresponding to M1, M2, C1, C2. Total is 27 bytes per voice.

  • Voice ID
  • FL & CON
  • Slot Mask
  • DT1 & MUL x 4
  • TL x 4
  • KS & AR x 4
  • AME & D1R x 4
  • DT2 & D2R x 4
  • D1R & RR x 4

MDX Commands

Each command consists of one byte, followed by specific parameters.

  • 0x00-0x7f • Rest +1 clock cycles
  • 0x80-0xdf n • Note data, followed by duration n + 1. Corresponds to MML command n#,#. 0x80 corresponds to MML o0d+, which means octave 0, note D♯. 0xdf corresponds to o8d, octave 8, D. To calculate the MIDI equivalent note, subtract 0x80 and add 3. For the PCM channels, P through W, this represents data number (???).
  • 0xff n • Set tempo to n. Equivalent to mml command @t#. Tempo applies to all tracks at the same time, not just current track.
  • 0xfe n m • Set OPM register n to value m.
  • 0xfd n • Set current voice.
  • 0xfc n • Pan.
  • 0xfb n • Set volume.
  • 0xfa • Decrease volume. Corresponds to MML command (.
  • 0xf9 • Increase volume. Corresponds to MML command ).
  • 0xf8 n • Sound length
  • 0xf7 • Disable key off for next note. Corresponds to MML command &, except it precedes the note instead of following it.
  • 0xf6 n 0x00 • Repeat n times until a Repeat end command.
  • 0xf5 nn • Repeat end. Loop back nn (signed word) bytes.
  • 0xf4 nn • Repeat escape. In the last repetition, skip nn bytes, thus shortening it.
  • 0xf3 nn • Detune nn/64 semitones. Corresponds to MML command D#.
  • 0xf2 nn • Portamento. Change pitch nn/16384 semitones per clock. This is issued before the starting note.
  • 0xf1 0x00 • Performance end.
  • 0xf1 nn • Performance end, but loop from nn bytes (nn is a negative int16).
  • 0xf0 n • Delay key-on n ticks. Corresponds to MML command k#.
  • 0xef n • Sync send on channel n. If channel n is in Sync Wait, resume playback on that channel. MML command S#
  • 0xee • Sync Wait on current channel. Pause playback on this channel until resumed by a Sync Send signal (see above). MML Command W.
  • 0xed n • ADPCM / noise frequency set to n. For FM channels (A-H), 0 means disable noise, 128+ means set noise frequency (without bit 7). For ADPCM channels (P-W), sets sampling frequency, corresponding to MML command F#.
  • 0xec 0x80 • Pitch LFO disable (MPOF).
  • 0xec 0x81 • Pitch LFO enable (MPON).
  • 0xec m nn aa • LFO Pitch control. m controls the waveform (0=sawtooth, 1=square, 2=triangle), nn is the frequency, expressed in clock cycles / 4, and aa is the amplitude.
  • 0xeb 0x80 • LFO Volume MAOF.
  • 0xeb 0x81 • LFO Volume MAON.
  • 0xeb m nn aa • LFO Volume control. Same as LFO Pitch.
  • 0xea 0x80 • LFO OPM MHOF.
  • 0xea 0x81 • LFO OPM MHON.
  • 0xea m n o p q • OPM LFO m=sync/wave, n=lfrq, o=pmd, p=amd, q=pms/ams (???)
  • 0xe9 n • Set LFO key-on delay. Corresponds to MML command MD#.
  • 0xe8 • PCM8 expansion/ mode shift. (???)
  • 0xe7 0x01 n • Fade-out at speed n.

External Links

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