GM, GS & XG: A Little History
Many sound cards and synthesizers, as well as most audio software, are compatible with one of the three midi norms (GM, GS, XG). Though MIDI has long since proven its utility, the existence of different standards can be confusing, so this article has been put together in order to clarify a few points.
For someone who just wants to listen to music, or for a multimedia developer looking to add background music or sounds to their program, the Midifile format has proven to be a real asset. It allows a user to play a sequence that was written by another person, whatever gear or software they were using. But in the past, only the notes and rhythm of the musician were encoded, which didn’t necessarily guarantee a similar sound. In fact, the sounds coming from each sound card, each synthesizer, were different (different in their sound and in their organization). Patch number 15 could be a piano on synthesizer X, and a trumpet on synthesizer Y. It was sometimes necessary to be an expert in MIDI and/or have a lot of patience to get the right settings in order to listen to a piece written by another musician working on a different synth or platform.
The MMA (Midi Manufacturers Association) fixed this problem in 1991 by creating the GM (General Midi) standard. The goal of this standard has been to unify the behavior of sound generators when playing back a Midifile sequence. In order to be labeled GM, an instrument must be multi-timbral and polyphonic up to at least 24 voices, and include at least 16 families of sounds (pianos, guitars, strings…), each containing 8 variations (for example, for strings: violin cello, double bass, etc…
The main advantage of this standardization is that each patch number now corresponds to a certain instrument no matter what the machine. So, instrument number 71 will always be a bassoon and number 12 a vibraphone. The sound generator must also contain a drum kit, whose mapping (placement of the separate elements on a keyboard) is also standardized. Finally, MIDI controllers must be recognized also.
To read the full detailed article including the GM reference guide see: MIDI The GM Standard and its Extensions.