GSS
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GSS, short for General Sound Set, is the name of DMX's support for using MIDI sound effects. Instead of using the standard MIDI format, GSS use DMX formats 1 and 2 (format 0 is used for PC speaker sound effects, format 3 is used for digitized sounds).
The Roland GS standard, a superset of General MIDI introduces the concept of instrument banks, which is used in these GSS sound formats; thanks to them there can be separate sound effect banks and melodic banks, so MIDI sound effects could be used without affecting the instruments used by MIDI music.
Format 1[edit]
This format allows to have simple sequences of notes played by a single instrument.
| Offset | Type | Description |
|---|---|---|
| 0x00 | Unsigned 16-bit LE int | Format number (must be 1) |
| 0x02 | Unsigned 16-bit LE int | Number of samples |
| 0x04 | Unsigned 16-bit LE int | MIDI bank |
| 0x06 | Unsigned 16-bit LE int | MIDI instrument |
| 0x08 | Unsigned 8-bit array | Samples |
The sample rate is 140 Hz. A sample with value zero is a note off, otherwise each sample value determines both the note and the pitch bend. The note and pitch bend portions are bitpacked into a single byte:
- note is equal to 28 plus the top 7 bits of the byte.
- pitch bend depends on the lowest bit of the byte: a value of 0 maps to a MIDI pitch bend of 159, while a value of 1 maps to a pitch bend of 127.
Format 2[edit]
This format only defines a single note.
| Offset | Type | Description |
|---|---|---|
| 0x00 | Unsigned 16-bit LE int | Format number (must be 2) |
| 0x02 | Unsigned 16-bit LE int | MIDI bank |
| 0x04 | Unsigned 16-bit LE int | MIDI instrument |
| 0x06 | Unsigned 16-bit LE int | Note |
| 0x08 | Unsigned 16-bit LE int | Note length |
