General MIDI (GM) is an extension that allows a MIDI sequence to sound
roughly the same on any GM-compatible sound module. It effects....
General MIDI
General MIDI (GM) is an extension that allows a MIDI sequence to sound
roughly the same on any GM-compatible sound module. It effects sound
modules, and does not change the MIDI specification for things like
sequencers or controllers.
GM requires that the sound module have a Polyphony of 32 notes, meaning that
the module can play at least 32 notes at the same time. It also requires
that a sound module be able to use all of the 16 MIDI channels at the same
time, so you can have up to 16 separate tracks (each with its own voice) in
a song.
General MIDI specifies a common Voice Bank of 128 sounds that must be in
every GM compatible module. Each voice is assigned a standard program change
number, so that you will always get a piano sound when you use program
change #0 (for example). However, each synthesizer can generate each sound
in its own way, so the piano sounds on different synthesizers may sound
significantly different.
A GM module defaults to play a drum kit on channel 10. There is also a
standard Drum Sound Map that specifies the note numbers (35-81) of 47
different drum sounds. So you will always find a snare sound at note number
38 and a bass sound at note number 35. It doesn't specify the timbre of the
sound, so you can have different snare sounds (at note number 38) in
different drum kits.
