General MIDI

General MIDI or GM is a standardized specification for music synthesizers that respond to MIDI messages. GM was developed by the American MIDI Manufacturers Association (MMA) and the Japan MIDI Standards Committee (JMSC) and first published in 1991. The official specification is available in English from the MMA, bound together with the MIDI 1.0 specification, and in Japanese from the Association of Musical Electronic Industry (AMEI).

GM imposes several requirements beyond the more abstract MIDI 1.0 specification. While MIDI 1.0 by itself provides a communications protocol which ensures that different instruments can interoperate at a fundamental level (e.g., that pressing keys on a MIDI keyboard will cause an attached MIDI sound module to play musical notes), GM goes further in two ways: it requires that all GM-compatible synthesizers meet a certain minimal set of features, such as being able to play at least 24 notes simultaneously (polyphony), and it attaches specific interpretations to many parameters and control messages which were left under-specified in the MIDI 1.0 spec, such as defining instrument sounds for each of the 128 possible program numbers.

GM synthesizers are required to be able to:

Allow 24 voices to be active simultaneously (including at least 16 melodic and 8 percussive voices)
Respond to note velocity
Support all 16 channels simultaneously (with channel 10 reserved for percussion)
Support polyphony (multiple simultaneous notes) on each channel

Parameter interpretations

GM Instruments must also obey the following conventions for program and controller events:

Program change events

In MIDI, the instrument sound or "program" for each of the 16 possible MIDI channels is selected with the Program Change message, which has a Program Number parameter. The following table shows which instrument sound corresponds to each of the 128 possible Program Numbers for GM only. There are 128 program numbers. The numbers can be displayed as values 1 to 128, or, alternatively, as 0 to 127. The 0 to 127 numbering is usually only used internally by the synthesizer; the vast majority of MIDI devices display these Program Numbers as shown in the table (1-128).^{[citation needed]}

Piano

Chromatic Percussion

Organ

Guitar

Bass

33 Acoustic Bass
34 Electric Bass (finger)
35 Electric Bass (pick)
36 Fretless Bass
37 Slap Bass 1
38 Slap Bass 2
39 Synth Bass 1
40 Synth Bass 2

Strings

41 Violin
42 Viola
43 Cello
44 Contrabass
45 Tremolo Strings
46 Pizzicato Strings
47 Orchestral Harp
48 Timpani

Ensemble

49 String Ensemble 1
50 String Ensemble 2
51 Synth Strings 1
52 Synth Strings 2
53 Choir Aahs
54 Voice Oohs
55 Synth Choir
56 Orchestra Hit

Brass

57 Trumpet
58 Trombone
59 Tuba
60 Muted Trumpet
61 French Horn
62 Brass Section
63 Synth Brass 1
64 Synth Brass 2

Reed

Pipe

Synth Lead

81 Lead 1 (square)
82 Lead 2 (sawtooth)
83 Lead 3 (calliope)
84 Lead 4 chiff
85 Lead 5 (charang)
86 Lead 6 (voice)
87 Lead 7 (fifths)
88 Lead 8 (bass + lead)

Synth Pad

89 Pad 1 (new age)
90 Pad 2 (warm)
91 Pad 3 (polysynth)
92 Pad 4 (choir)
93 Pad 5 (bowed)
94 Pad 6 (metallic)
95 Pad 7 (halo)
96 Pad 8 (sweep)

Synth Effects

97 FX 1 (rain)
98 FX 2 (soundtrack)
99 FX 3 (crystal)
100 FX 4 (atmosphere)
101 FX 5 (brightness)
102 FX 6 (goblins)
103 FX 7 (echoes)
104 FX 8 (sci-fi)

Ethnic

105 Sitar
106 Banjo
107 Shamisen
108 Koto
109 Kalimba
110 Bagpipe
111 Fiddle
112 Shanai

Percussive

113 Tinkle Bell
114 Agogo
115 Steel Drums
116 Woodblock
117 Taiko Drum
118 Melodic Tom
119 Synth Drum
120 Reverse Cymbal

Sound effects

121 Guitar Fret Noise
122 Breath Noise
123 Seashore
124 Bird Tweet
125 Telephone Ring
126 Helicopter
127 Applause
128 Gunshot

Percussion

GM Standard Drum Map

In GM standard MIDI files, channel 10 is reserved for percussion instruments only. Notes recorded on channel 10 always produce percussion sounds when transmitted to a keyboard or synth module which uses the GM standard. Each of the 128 different possible note numbers correlate to a unique percussive instrument, but the sound's pitch is not relative to the note number.

If a MIDI file is programmed to the General MIDI protocol, then the results are predictable, but the sound fidelity may vary depending on the quality of the GM synthesizer:

35 Bass Drum 2
36 Bass Drum 1
37 Side Stick/Rimshot
38 Snare Drum 1
39 Hand Clap
40 Snare Drum 2
41 Low Tom 2
42 Closed Hi-hat
43 Low Tom 1
44 Pedal Hi-hat
45 Mid Tom 2
46 Open Hi-hat
47 Mid Tom 1
48 High Tom 2
49 Crash Cymbal 1
50 High Tom 1
51 Ride Cymbal 1
52 Chinese Cymbal
53 Ride Bell
54 Tambourine
55 Splash Cymbal
56 Cowbell
57 Crash Cymbal 2
58 Vibra Slap
59 Ride Cymbal 2
60 High Bongo
61 Low Bongo
62 Mute High Conga
63 Open High Conga
64 Low Conga
65 High Timbale
66 Low Timbale
67 High Agogô
68 Low Agogô
69 Cabasa
70 Maracas
71 Short Whistle
72 Long Whistle
73 Short Güiro
74 Long Güiro
75 Claves
76 High Wood Block
77 Low Wood Block
78 Mute Cuíca
79 Open Cuíca
80 Mute Triangle
81 Open Triangle

Controller events

In MIDI, adjustable parameters for each of the 16 possible MIDI channels may be set with the Control Change message, which has a Control Number parameter and a Control Value parameter. GM also specifies which operations should be performed by multiple Control Numbers:^[1]

1 Modulation wheel 7 Volume 10 Pan 11 Expression 64 Sustain pedal 100 Registered Parameter Number LSB 101 Registered Parameter Number MSB 121 All controllers off 123 All notes off

RPN

GM defines several Registered Parameters, which act like Controllers but are addressed in a different way. In MIDI, every Registered Parameter is assigned a Registered Parameter Number or RPN. Registered Parameters are usually called RPNs for short.

Setting Registered Parameters requires sending (numbers are decimal):

two Control Change messages using Control Numbers 101 and 100 to select the parameter, followed by
any number of Data Entry messages of one or two bytes (MSB = Controller #6, LSB = Controller #38), and finally
an "End of RPN" message

The following global Registered Parameter Numbers (RPNs) are standardised ^[2] (the parameter is specified by RPN LSB/MSB pair and the value is set by Data Entry LSB/MSB pair):

0,0 Pitch bend range 1,0 Channel Fine tuning 2,0 Channel Coarse tuning

For example: RPN control sequence to set coarse tuning to A440 (parm 2, value 64):
101:0, 100:2, 6:64, 101:127, 100:127

System Exclusive messages

Two GM System Exclusive ("SysEx") messages are defined: one to enable and disable General MIDI compatibility mode (for synthesizers that also have non-GM modes); and the other to set the synthesizer's master volume.

GS extensions

A superset of the General MIDI standard which added several proprietary extensions. The most notable addition was the ability to address multiple banks of programs (instrument sounds) by using an additional pair of Bank Select controllers to specify up to 16384 "variation" sounds (cc#0 is Bank Select MSB, and cc#32 is Bank Select LSB). Other most notable features were 9 Drum kits with 14 additional drum sounds each, simultaneous Percussion Kits - up to 2 (Channels 10/11), Control Change messages for controlling the send level of sound effect blocks (cc#91-94), entering additional parameters (cc#98-101), portamento, sostenuto, soft pedal (cc#65-67), and model-specific SysEx messages for setting various parameters of the synth engine.

GS was introduced in 1991 with the Roland Sound Canvas line, which was also Roland's first General MIDI synth module.

General MIDI Level 2

In 1999, the official GM standard was updated to include more controllers, patches, RPNs and SysEx messages, in an attempt to reconcile the conflicting and proprietary Roland GS and Yamaha XG additions. Here's a quick overview of the GM2 changes in comparison to GM/GS:

Number of Notes - minimum 32 simultaneous notes
Simultaneous Percussion Kits - up to 2 (Channels 10/11)
Up to 16384 variation banks are allowed, each containing a version of the 128 Melodic Sounds (the exact use of these banks is up to the individual manufacturer.)
9 GS Drum kits are included
Additional Control Change messages
- Filter Resonance (Timbre/Harmonic Intensity) (cc#71)
- Release Time (cc#72)
- Attack time (cc#73)
- Brightness/Cutoff Frequency (cc#74)
- Decay Time (cc#75)
- Vibrato Rate (cc#76)
- Vibrato Depth (cc#77)
- Vibrato Delay (cc#78)
Registered Parameter Numbers (RPNs)
- Modulation Depth Range (Vibrato Depth Range)
Universal SysEx messages
- Master Volume, Fine Tuning, Coarse Tuning
- Reverb Type, Time
- Chorus Type, Mod Rate, Mod Depth, Feedback, Send to Reverb
- Controller Destination Setting
- Scale/Octave Tuning Adjust
- Key-Based Instrument Controllers
- GM2 System On SysEx message

Additional melodic instruments can be accessed by setting CC#0 to 121 and then using CC#32 to select the bank before a Program Change.

References

↑ MIDI Messages technical specification Table 3 - Control Change Messages (Data Bytes)
↑ General MIDI 1, 2 and Lite Specifications

Official MIDI Standards Organizations

MIDI Manufacturers Association (MMA) - Source for English-language MIDI specs
Association of Musical Electronics Industry (AMEI) -Source for Japanese-language MIDI specs

External links

[1] MIDI Messages technical specification Table 3 - Control Change Messages (Data Bytes)

[2] General MIDI 1, 2 and Lite Specifications

[1]

[2]