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For more information on this article, visit the GENMIDI page on the Doom Wiki.

The GENMIDI lump is used in Doom and other Doom-engine games to initialize the registers for the MIDI instruments in an OPL chip. ZDoom has an OPL emulation feature and can make use of this lump.

Lump format


The lump has an 8-byte ASCII header, containing the text "#OPL_II#".

Instrument data

The header is followed by 175 36-byte records of instrument data. Records are little-endian.

Each record has a 4 byte header of the following form, followed by two 16-byte records of OPL voice data. If the double voice bit is set in the header, both voices will be played simultaneously; otherwise, only the first set of voice data is played.

Offset Size (bytes) Description
0-1 2 Flags: a bitfield that control the record.
Bit Hex Description
0 0x01 Fixed pitch - Instrument always plays the same note. Most MIDI instruments play a note that is specified in the MIDI "key on" event, but some (most notably percussion instruments) always play the same fixed note.
1 0x02 Unknown - used in instrument #65 of the Doom GENMIDI lump.
2 0x04 Double voice - Play two voices simultaneously. This is used even on an OPL2 chip. If this is not set, only the first voice is played. If it is set, the fine tuning field (see below) can be used to adjust the pitch of the second voice relative to the first.
2 1 Fine tuning - This normally has a value of 128, but can be adjusted to adjust the tuning of the instrument. This field only applies to the second voice of double-voice instruments; for single voice instruments it has no effect. The offset values are similar to MIDI pitch bends; for example, a value of 82 (hex) in this field is equivalent to a MIDI pitch bend of +256.
3 1 Note number used for fixed pitch instruments (see below)
4 1 Modulator Tremolo / vibrato / sustain / KSR / multi
5 1 Modulator Attack rate / decay rate
6 1 Modulator Sustain level / release rate
7 1 Modulator Waveform select
8 1 Modulator Key scale level
9 1 Modulator Output level
10 1 Feedback
11 1 Carrier Tremolo / vibrato / sustain / KSR / multi
12 1 Carrier Attack rate / decay rate
13 1 Carrier Sustain level / release rate
14 1 Carrier Waveform select
15 1 Carrier Key scale level
16 1 Carrier Output level
17 1 Unused
18-19 2 Base note offset. This is used to offset the MIDI note values. Several of the GENMIDI instruments have a base note offset of -12, causing all notes to be offset down by one octave.
20-35 16 Second voice, same layout as 4-19.

External links

  • OPL3 Bank Editor - a utility that allows the editing and creation of own GENMIDI banks.