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General MIDI

Who? What? Why? When?


More and more modules and keyboards are now General MIDI compatible. GM is supposed to make your life easier - but what the hell is it all about? Paul White explains.

Somewhere between the big bang and the death of the universe, man invented MIDI. Unlike many other of man's inventions, such as nuclear weapons, genetically engineered diseases and fast food (the last two may be considered interchangeable), MIDI was, on the whole, a good thing. Over the years we've come to terms with MIDI's little foibles and eccentricities, and every time we seem in danger of outgrowing it, another chunk gets added to the protocol to further extend its power and usefulness.

General MIDI-compatible equipment has been with us for two years now, but I get the feeling that most 'serious' MIDI users consider it to be some form of distracting and largely irrelevant 'consumer' addition. I confess that I tended to lean towards that way of thinking until clients started to arrive at my studio clutching GM MIDI song files which they wanted turned into usable backing tapes for their solo club gigs. Assigning appropriate sounds from a variety of non-GM modules takes time, and though a little judicious mapping can help here, a dedicated GM module makes life a lot easier. So, for the benefit of the uninitiated, what is General MIDI, or GM, as it is known to its friends?

GENERAL MIDI



Without getting in too deep, General MIDI is another stage of standardisation which has been added to the existing MIDI protocol to enable manufacturers to build synthesizers and synth modules that exhibit a specified degree of compatibility in certain areas. Specifically, General MIDI sets out strict rules for patch mapping, drum note mapping, multitimbrality and polyphony. In a nutshell, the aim is to allow a MIDI sequence recorded using one GM module to be played back on any other GM module without the need to remap patches, move drum note allocations or worry about running out of parts or polyphony. This doesn't mean that all GM synths have to sound exactly the same, but it does mean that, for example, a piano preset on one machine must be in the same patch location as a similar piano preset on any other GM machine.

MIDI COMPATIBILITY



Normally, whenever you record a piece of music using a sequencer, you insert patch change commands at the start of the piece, and at any subsequent locations in the piece where a sound is required to change. That way, whenever you play back the sequence through the same instruments and modules, the correct sounds will automatically be called up with no intervention on your behalf. However, if you play the sequence back on a friend's MIDI system, you may well find that all the sounds are completely wrong because the patches are not only completely different in sound, but any that are suitable are also stored in different patch locations. In the case of programmable instruments, this kind of chaos is difficult to avoid because most users have their own system for storing their edited sounds. Furthermore, the factory presets that come with most MIDI instruments were not stored in any particular order prior to the introduction of GM.

Another potential stumbling block is the drum and percussion part. Is your friend's system set up with the drum part on the same MIDI channel and, if so, are the drum sounds mapped to the same notes? Roland have had their own more or less standard drum mapping system for some time now, but some other manufacturers have not been so well organised. Furthermore, you may have written the piece using drum sounds that don't have any close equivalent on your friend's drum machine.

Let's say you're lucky and you get all the sounds mapped out. There's still a good chance you'll come unstuck when it comes to controller information; perhaps one of the modules doesn't respond to Controller 7 (Master Volume), or perhaps the pitch bend ranges are set differently to those on your own system.

The problem was that, although MIDI was a wonderful system, for many applications there was too much that was still optional. General MIDI was devised to provide a solution for use in situations where a high degree of compatibility was essential, for example when replaying prerecorded MIDI song files. Now, with the introduction of general MIDI, musicians can play each other's GM song files and be confident that they will sound more or less the way they should, even though there are subtle subjective differences between one manufacturer's GM machine and another. This has opened up the market for commercially available MIDI song files, and though these hold little attraction for the serious composer, they are very effective as live backings and may also be used to gain recording, mixing and effects processing experience.

POLYPHONY AND MULTITIMBRALITY



The problem with polyphony and multitimbrality is that you can never have enough of it! GM MIDI instruments provide the ability to play back 16 parts on 16 MIDI channels, but is a total polyphony of 24 notes sufficient to go round? If not, note robbing takes place and previously played notes start to drop out. The answer has to be that more would be nice, but we'll have to be grateful for what we get. What's more, where a synth uses two voices to make up a sound, the actual polyphony is further reduced. In theory, that means that a GM song file written for one GM machine could still come unstuck if played back using a different GM module claiming that number of voices and polyphony mean the same thing.

ROLAND'S ENHANCED GS FORMAT



Much of the present GM format owes its existence to Roland's own protocols, so it's hardly surprising that Roland have gone one step further and devised an enhanced version of General MIDI which they call GS. Realising that many users wouldn't be satisfied with 128 preset sounds, Roland have designed their GS machines to offer several alternative banks of sounds, the basic GM set (Capital Tones) being the first bank (Bank 0). There are up to seven 'Variation Tones' based on each of the Capital Tones and these are arranged so as to have the same program change numbers as the tones from which they are derived. In other words, all the variation tones of a Piano Capital Tone will still be pianos, though they will all be subtly different. Further banks are provided for sounds known as Sub-Capital Tones, which are less obviously related to the Capital Tones.

A Bank Change (in Roland's case based on Controller 0) allows the user to switch between the various banks. Conventional program change commands are then used to select the sounds within each bank — a neat way to get around MIDI's limitation of being able to directly address only 128 patches.

EDITING



Because General MIDI is based on the concept of the same sounds always being in the same place, it stands to reason that any attempt at editing the sounds will risk negating any advantages the system has. Some modules allow editing, though the patch name remains unchanged, while others retain the GM sounds as presets.

COMMERCIAL MIDI SONG FILES



Over the past couple of years, companies have sprung up marketing GM song files covering all musical styles from pop to classical. These have many applications, from general interest to song analysis, but the area that has attracted the most interest is as an alternative to backing tapes for cabaret performers. Providing the originators of the disk pay MCPS (Mechanical Copyright Protection Society) royalties and the performer plays in a venue registered with PRS (Performing Rights Society), nobody loses out. A huge advantage of MIDI song files over pre-recorded backing tapes is that the key can be changed at the touch of a button, making life rather less difficult for the solo entertainer. The overall sound quality is generally better too; with pre-recorded tapes, you either have to play the original night after night and risk wearing it out, or copy it onto another cassette with the consequent loss of quality.

GENERAL MIDI REQUIREMENTS

In 1991, General MIDI was ratified with the aim of defining a minimum set of MIDI capabilities to which all GM MIDI devices must adhere. The main points are as follows:

A GM instrument must support all 16 MIDI channels simultaneously to provide 16-part multitimbrality.

Percussion parts must be on MIDI channel 10, a minimum set of 47 standard sound types, including the most common drum and latin percussion sounds, must be provided and these must all be mapped in accordance with the GM standard. This mapping owes a lot to Roland's original mapping system.

GM instruments must be capable of 24-note polyphony and notes must be allocated dynamically. However, the specification allows eight notes to be reserved for percussion, leaving 16 for the other instruments.

All 128 preset sounds are defined as to their type and patch location. Though there is some variation in sound between one module and another, the instrument type (and even playing style in the case of basses, for example) for each patch location is quite rigidly defined, right down to the dog barks and gun shots in the special effects section. Some of the sounds, such as pads, are a little more flexible but they must still be of a roughly similar tone and style.

All GM instruments must respond to the same set of MIDI Controllers. The MIDI Controller implementation includes the ability to change the master tuning and Pitch Bend wheel range via MIDI, Reset All Controllers, (which resets all MIDI Controllers to their default values), and All Notes Off. All GM machines must also respond to Pitch Bend and Aftertouch.


GM SOUND SET

1: Piano 1 2: Piano 2
3: Piano 3 4: Honky-tonk Pno.
5: E. Piano 1 6: E. Piano 2
7: Harpsichord 8: Clav
9: Celesta 10: Glockenspiel
11: Music Box 12: Vibraphone
13: Marimba 14: Xylophone
15: Tubular-Bell 16: Santur
17: Organ 1 18: Organ 2
19: Organ 3 20: Church Org 1
21: Reed Organ 22: Accordion Fr
23: Harmonica 24: Bandneon
25: Nylon-Str Guitar 26: Steel-Str Guitar
27: Jazz Guitar 28: Clean Guitar
29: Muted Guitar 30: Overdr. Guitar
31: Distortion Guitar 32: Guit. Harmonics
33: Acoustic Bass 34: Fingered Bass
35: Picked Bass 36: Fretless Bass
37: Slap Bass 1 38: Slap Bass 2
39: Synth Bass 1 40: Synth Bass 2
41: Violin 42: Viola
43: Cello 44: Contrabass
45: Tremelo Str. 46: Pizzicato Str.
47: Harp 48: Timpani
49: Strings 50: Slow Strings
51: Syn Strings 1 52: Syn Strings 2
53: Choir Aahs 54: Voice Oohs
55: Syn Vox 56: Orch. Hit
57: Trumpet 58: Trombone
59: Tuba 60: Muted Trumpet
61: French Horn 62: Brass 1
63: Synth Brass 1 64: Synth Brass 2
65: Soprano Sax 66: Alto Sax
67: Tenor Sax 68: Baritone Sax
69: Oboe 70: English Horn
71: Bassoon 72: Clarinet
73: Piccolo 74: Flute
75: Recorder 76: Pan Flute
77: Bottle Blow 78: Shakuhachi
79: Whistle 80: Ocarina
81: Square Wave 82: Saw Wave
83: Syn Calliope 84: Chiffer Lead
85: Charang 86: Solo Vox
87: 5th Saw Wave 88: Bass & Lead
89: Fantasia 90: Warm Pad
91: Polysynth 92: Space Voice
93: Bowed Glass 94: Metal Pad
95: Halo Pad 96: Sweep Pad
97: Ice Rain 98: Soundtrack
99: Crystal 100: Atmosphere
101: Brightness 102: Goblin
103: Echo Drops 104: Star Theme
105: Sitar 106: Banjo
107: Shamisen 108: Koto
109: Kalimba 110: Bagpipe
111: Fiddle 112: Shannai
113: Tinkle Bell 114: Agogo
115: Steel Drums 116: Wood Block
117: Taiko 118: Melo.Tom 1
119: Synth Drum 120: Reverse Cym
121: Gt. Fret Noise 122: Breath Noise
123: Sea Shore 124: Bird
125: Telephone 1 126: Helicopter
127: Applause 128: Gunshot


SOME CURRENT GM SYNTHS

Roland SC55, SC155, SC7 and JW50
Boss DS660 Dr Synth
Dream GMX1
Kawai GMega
Korg 03R/W
Yamaha TG100


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Shape Of Things To Come

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Space... The Final Frontier


Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.

 

Sound On Sound - Aug 1993

Topic:

MIDI


Feature by Paul White

Previous article in this issue:

> Shape Of Things To Come

Next article in this issue:

> Space... The Final Frontier


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