"General MIDI" is not the same as MIDI. Where MIDI is a language, a file format, and a connector specification, the "General MIDI System Level 1" specification -- also known as "GM" and later renamed General MIDI 1 or "GM1") defines specific features of a MIDI instrument. Without General MIDI, playback of MIDI files created on one MIDI instrument might sound totally different on a different MIDI instrument, because the only sound definition in MIDI is the sound number (Program Number), not the actual characteristics of the sound. GM helped establish a consistent level of performance compatibility among MIDI instruments by establishing that specific sounds should be selected by certain Program Numbers, paving the way for MIDI data to be used in computer games and cell phones.

Note: The General MIDI (GM1) specification was superceded in 1999 by General MIDI 2 which supports additional features and capabilities commonly available. However, GM1 remains a popular format for lower-cost synthesizers and is commonly used for music distributed as Standard MIDI Files. General MIDI Lite is an even lower-cost version of GM developed specifically for use in low-power portable devices such as cell phones.

GM1 Features

To be GM1 compatible, a GM1 sound generating device (keyboard, sound module, sound card, IC, software program or other product) must meet the General MIDI System Level 1 performance requirements outlined below, instantaneously upon demand, and without additional modification 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 GM1 Instrument Patch Map and 47 percussion sounds which conform to the GM1 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.

• Other Messages: Respond to the data entry controller and the RPNs for fine and course tuning and pitch bend range, as well as all General MIDI Level 1 System Messages.

The MMA's GM Developer Guidelines document describes additional recommendations and clarifications of the GM Specification for content producers and device makers, to insure improved compatibility among GM products.

The GM1 Logo was created to insure consumer recognition for products that meet the General MIDI Level 1 Specification. The GM Logo is the property of the MMA and AMEI and must be used in accordance with guidelines established to insure the value of the GM Logo for our members and for the consumer.

The General MIDI Lite Specification describes one of two platforms for mobile MIDI communication that have been approved and adopted as a standard by the MIDI industry. This document has three primary components:

• A specification called General MIDI Lite (GM Lite), which defines a new level of tone generation (sound module) device
• Authoring guidelines for music data in SMF (Standard MIDI File) format that is intended for playback on GM Lite devices
• Implementation guidelines for GM Lite file players .

GM Lite vs. SP-MIDI

The General MIDI Lite specification defines a fixed-polyphony MIDI device, intended to meet a particular set of current and future market needs. The Scalable Polyphony MIDI (SP-MIDI) Specification compliments GML by defining flexible polyphony MIDI devices and content. Developers of GM Lite players are strongly advised to keep as much flexibility as possible in how their players handle channel priorities, drum channels and other System messages. This will make it far easier for their products to be compatible with song data authored for the Scalable Polyphony MIDI specification.

GM Lite vs. GM 1

The General MIDI Lite device specification is intended for equipment that does not have the capability to support the full feature set defined in General MIDI 1.0, on the assumption that the reduced performance may be acceptable (and even required) in some mobile applications. GM Lite represents just one standardized set of performance capabilities for portable applications - other performance levels are likely to be standardized in the future.

GM Lite Features

• Requirements
  Number of Notes: 16 simultaneous notes
  MIDI Channels: 16
  - Simultaneous Melodic Instruments = up to 15
  - Simultaneous Percussion Kits = 1 (Channel 10)
  
• Control Change Messages
  - Modulation Depth (cc#1)
  - Channel Volume (cc#7)
  - Pan (cc#10)
  - Expression (cc#11)
  - Data Entry (cc#6/38)
  - Hold1 (Damper) (cc#64)
  - RPN LSB/MSB (cc#100/101)
  - Pitch Bend
  - All Sound Off, All Notes Off, Reset All Controllers
  
• Registered Parameter Numbers
  - Pitch Bend Sensitivity
  
• Universal System Exclusive Messages
  - GM1 System On
  
• GM Lite Instrument Sound Set
• GM Lite Percussion Sound Set

For complete details on GML features and MIDI message syntax, please consult the General MIDI Lite Specification (see below to order).

GM Lite Developer Information

Recommended guidelines for Using GM Lite in Mobile Applications are included in the GM Lite Specification document. Developers are also urged to consult the GM1 Developer Guidelines (included in the Complete MIDI 1.0 Specification).

The GML Logo was created to insure consumer recognition for products that meet the General MIDI Lite Specification. The GM Logos are the property of the MMA and AMEI and must be used in accordance with guidelines established to insure the value of the GM Logos for our members and for the consumer.