MIDI Manufacturers Association


General MIDI System Level 1

In September of 1991 the MIDI Manufacturers Association and the Japan MIDI
Standards Committee created the beginning of a new era in MIDI technology,
by adopting the "General MIDI System - Level 1" specification (GM). The
specification is designed to provide a minimum level of performance
compatibility among MIDI instruments, and help pave the way for MIDI to
become a part of the growing consumer and multimedia markets.

Detailed information on General MIDI and MIDI is available in the official
MMA Complete MIDI 1.0 Detailed Specification document published by the
MMA. Developers may also want to obtain the GM Survey and Developer
Guidelines document to assist with GM compatibility issues.


Overview of General MIDI

GM Hardware Features:

To be GM compatible, a sound generator (keyboard, sound module, sound card
or similar products) must meet the General MIDI System - Level 1
performance requirements outlined below, and without additional
modification, accessories or adjustment/configuration by the user.


Voices: 
	A minimum of either 24 fully dynamically allocated voices are
	available simultaneously for both melodic and percussive sounds, or 
	16 dynamically allocated voices are available for melody plus 8 for
	percussion. All voices respond to velocity.

Channels: 
	All 16 MIDI Channels are supported. Each Channel can play a
	variable number of voices (polyphony). Each Channel can play a 
	different instrument (sound/patch/timbre).  Key-based percussion 
	is always on MIDI Channel 10.

Instruments: 
	A minimum of 16 simultaneous and different timbres playing
	various instruments. A minimum of 128 preset instruments 
	(MIDI program numbers) conforming to the GM Instrument Patch Map 
	and 47 percussion sounds which conform to the GM Percussion Key Map.

Channel Messages: 
	Support for continuous controllers 1, 7, 10, 11, 64, 121 and 123;
	RPN #s 0, 1, 2; Channel Pressure, Pitch Bend.



GM Sound Set Compatiblity:

General MIDI's most recognized feature is the defined list of sounds or
"patches". However, General MIDI does not actually define the way the
sound will be reproduced, only the name of that sound. 

Though this can obviously result in wide variations in performance from
the same song data on different GM sound sources, the authors of General
MIDI felt it important to allow each manufacturer to have their own ideas
and express their personal aesthetics when it comes to picking the exact
timbres for each sound.

Each manufacturer must insure that their sounds provide an acceptable
representation of song data written for General MIDI. Guidelines for
developing GM compatible sound sets and song data are available through
the MMA.

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