A 1991 patch list made MIDI files sound the same everywhere

The system

MIDI 1.0, the protocol letting musical instruments and software exchange digital performance data, was first published in 1983, according to the MIDI Manufacturers Association's own specifications page, which describes it as 'the outcome of collaboration between various manufacturers.' That original protocol defined how messages such as note-on and note-off travel between devices, but it left the mapping between a MIDI 'program number' and an actual instrument sound entirely up to each manufacturer. General MIDI (GM) is a separate, later specification that closed that gap: a standardized sound-and-percussion map layered on top of the 1983 protocol.

What the documents establish

The General MIDI System Level 1 specification itself, published by the MIDI Manufacturers Association and carrying the copyright date 1991, states its purpose directly: without it, 'the sound that plays on MIDI note messages sent over channel one, program number one, is determined by the individual synthesizer manufacturer,' making shared MIDI files unreliable across devices. The specification fixes this with a minimum of 128 instrument presets, the GM Sound Set, mapped to standard program numbers, plus a Percussion Map assigning drum sounds to note numbers on MIDI channel 10, reserved permanently for key-based percussion. It also sets minimum polyphony (24 voices, or 16 melodic plus 8 percussion), a default pitch-bend range, and standard controller assignments, and notes it was developed jointly with Japan's MIDI Standards Committee. This 1991 sound-mapping standard is distinct from, and layered on top of, the 1983 MIDI 1.0 protocol defining the underlying messages.

Craft and rights

For anyone working with symbolic music, including MIDI files generated by an AI composition tool, General MIDI is what makes portability possible: a file built against the GM Sound Set will call up something recognizable as a piano or a snare drum on any compliant device, human-made or AI-generated alike, because the mapping lives in the playback hardware or software, not in the file's origin. That portability is purely technical; General MIDI's specification says nothing about authorship, licensing or the copyright status of a composition, and a GM-compliant file carries no information about whether it was composed by a person, generated by a model, or some mixture of both. Treating GM compliance as evidence of anything beyond playback compatibility would be a category error.

Outcomes and open questions

General MIDI Level 1 was superseded for expanded use cases by General MIDI 2 in 1999, per the MIDI Manufacturers Association's own page, though GM1 remains, in the association's words, 'a popular format' for distributed Standard MIDI Files, so tooling built around AI-generated symbolic music still has to account for which GM level a given output or import target assumes.

• Does a symbolic-music tool's output target General MIDI 1, General MIDI 2, or neither, and does the receiving software match?
• Is GM-standard playback compatibility being confused with any claim about a file's authorship or licensing?
• Where a file's percussion sounds wrong on playback, is the cause a non-GM-compliant device rather than the file itself?

A patch-numbering standard from 1991 still quietly decides whether a generated MIDI file sounds like a piano or noise on the device it lands on.