GM / GM2 / GS Reference

1. Overview

General MIDI (GM) is a standardized set of 128 instrument sounds and a percussion map that ensures any GM-compatible device plays back a MIDI file with roughly the right timbres. Three levels of the standard exist in the wild:

• GM1 (1991) — 128 melodic programs, 47 percussion sounds on channel 10, 24-voice polyphony minimum.
• GM2 (1999) — adds bank-select variations, 9 drum kits, effects control, 32-voice polyphony, and a second drum channel (ch 11).
• Roland GS (1991+) — Roland’s superset of GM1 that predates GM2. Uses CC#0 for variation tones and CC#32 for sound-map generation (SC-55, SC-88, SC-88Pro, SC-8820/8850).

All three are backward-compatible: a plain GM1 sequence plays correctly on GM2 and GS devices because unrecognized bank-select values fall back to the base GM sound.

2. GM Program List (0–127)

Program Change values are 0-indexed (the value on the wire). Some manuals show 1–128 — subtract 1 to get the PC number used by LJam’s patch field.

3. GM Drum Map (Channel 10)

These 47 percussion sounds are defined by GM1 and must be present on any compliant device. All are triggered on MIDI channel 10.

GM2 Drum Kits

GM2 defines 9 drum kits selectable via Program Change on the drum channel. The note mapping within each kit follows the same layout above but with different timbres:

4. GM2 Additions

General MIDI Level 2 (1999) is a strict superset of GM1. Any GM1 sequence plays correctly on a GM2 device.

Key Improvements

• 32-voice polyphony minimum (GM1 required 24).
• 16-part multitimbral — every channel active simultaneously.
• Second drum channel on channel 11 (GM1 only defined channel 10).
• 256+ melodic sounds via Bank Select variations of the 128 base programs.
• 9 drum kits selectable by Program Change on the drum channel.
• Reverb and chorus controllable via CCs and SysEx.

Useful Control Changes

5. Roland GS Bank Select

Roland’s GS standard (introduced with the SC-55 in 1991) extends GM with hundreds of additional sounds accessed via Bank Select. The two bank-select CCs have specific roles in the GS world:

CC#0 — Bank Select MSB (Variation Number)

• 0 = Capital Tone — the base GM sound for that program.
• 1–127 = Variation tones — alternate timbres in the same family. For example, PC 0 (Acoustic Grand Piano) with MSB 1 = Wide Piano, MSB 2 = Dark Piano.

On a plain GM device, CC#0 is ignored, so the base sound plays — GS files degrade gracefully.

CC#32 — Bank Select LSB (Sound Map)

On multi-generation devices like the SC-8820, the LSB selects which “era” of sounds to draw from:

Higher-numbered maps include everything from lower maps plus additional sounds. For GM-only devices (like FluidSynth), the LSB is irrelevant and safely ignored.

Message Sequence

A full GS patch selection requires three messages in order, all on the same channel:

1. CC#0 (MSB) — variation number
2. CC#32 (LSB) — sound map
3. Program Change — instrument number

All three must arrive before the next note plays.

GS vs GM2 vs XG

6. Using in LJam

LJam’s patch field on each track sends the full CC#0 + CC#32 + Program Change sequence. Three formats are supported:

Use ↑ / ↓ while the field is focused to nudge whichever number the cursor is on. See the Patch / Program Change section in the main docs for full details.