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General MIDI - Why You Need It
by Michael Tyler
Computer Music Products

If you are just getting started with MIDI/music applications, the biggest favor you could do for yourself is to make certain you purchase a "General MIDI" compatible instrument. Although particularly handy for beginners, those of us who have been around the block a few times with MIDI greatly appreciate how much simpler owning at least one General MIDI instrument has made our "MIDI lives"! General MIDI is not something that applies to just any MIDI instrument (as many newcomers mistakenly believe), so it's important to understand what General MIDI actually is.
First, I'll give you the short definition...

GENERAL MIDI: A recommended specification for consumer electronic MIDI instruments that includes a uniform numbering of instrumental and drum sounds.

General MIDI - Where Did It Come From?

One of the main problems that had caused headaches for MIDI users, was the inconsistent way that various instrument sounds were numerically arranged between different brands of MIDI synthesizers. On one synthesizer, instrument sound #1 might be piano, while on another it could be some weird sound like "aeroglide." You never knew. It was a salad toss- the instrument and drum sounds were numbered and arranged in completely different orders, from one brand to the next! Because of this inconsistency, it was difficult to share MIDI songs with one another and precluded the widespread availability of commercially produced MIDI songfiles. They simply would not playback properly without considerable intervention from the recipient of the songfile. This often required complete reassignment of instrument and drum sounds for each recorded track. Putting it mildly, it was very confusing and frustrating if you tried to play a MIDI song on anything other than the same brand and model synthesizer it was originally composed on. Fortunately, there is now a solution to this problem.

Several years ago, Roland Corporation and Passport Designs spearheaded an effort to establish a new minimum "industry standard" for MIDI instruments. The basic idea was to create a universal, specific preset instrument and drum setting that any manufacturer could easily include within their synthesizers. This new specification became known as "General MIDI." If this idea was accepted, GM could eliminate several of the problems and complexities that the MIDI composer had previously faced. In other words, there would finally be reasonable assurance that his or her composition would play back properly with the intended instrument and drum sounds, regardless of the brand of synthesizer being used. More importantly, this would also establish a "consumer level" MIDI standard that would require far less effort to master for those without a great deal of technical expertise. Sound like a good idea? Practically everyone else thought so, too. It was an idea whose time had come. Immediately after Roland unveiled the first General MIDI product in 1991, GM compatibility became one of the most significant developments in recent MIDI history and is now an industry staple.

General MIDI - "Recommended Practice"

The GM standard has been embraced by all companies who produce MIDI songfiles, nearly all synthesizer manufacturers, soundcard makers, and music software publishers. Yet, believe it or not, General MIDI is still an unofficial and largely unregulated standard! Compliance is strictly voluntary among these companies (however, if they chose to ignore the GM specification, they would lose a lot of business!). So, General MIDI compliance is considered recommended practice, but it is not a feature that any company is absolutely required to include in their MIDI products. In fact, not every MIDI instrument on the market today will have a General MIDI compatible mode of operation. It's up to you to make sure that the instrument you wish to purchase sports the GM compatibility logo. That way you know that it will be current with today's MIDI hardware, software, and commercial MIDI songfiles. Here are the important "minimum features" that a General MIDI compatible instrument will offer...

• A Standard set of 128 sounds to choose from when composing musical soundtracks.
  The sounds are always arranged in a specific numerical order from brand-to-brand.
  

• The capability of simultaneous playback of up to 16 separate instrument parts.
  The technical term is multitimbral - a basic GM instrument is, therefore, 16 Part Multitimbral.
  

• A minimum of 24-voice playback (sometimes incorrectly called 24 -note playback).
  The technical term for this feature is polyphony - a GM instrument has at least 24 Voice Polyphony.
  

• At least one Standard Drum Set or Kit.
  The percussion sounds always have the same note assignments from brand-to-brand.

Let me give you a bit more detail on each of the features listed above... 

The Standard 128 GM Sounds
There are a total of 128 GM sounds, organized into 16 "families" containing 8 sounds per "family" (8 X 16 = 128). The 16 families are:

PIANO, CHROMATIC PERCUSSION, ORGAN, GUITAR, BASS, STRINGS, ORCHESTRA ENSEMBLE, BRASS, REED, PIPE, SYNTH LEAD, SYNTH PAD, SYNTH EFFECTS, ETHNIC, PERCUSSIVE, and SOUND EFFECTS. 

16 Part Multitimbral
When MIDI synthesizers first became available in the early 1980's, they could only transmit and receive on just one out of a possible 16 MIDI channels. A single channel = a single sound. To achieve an ensemble playback of different sounds, you had to hook several MIDI synthesizers together, each assigned its own personal MIDI channel and instrument sound. Then, for multitimbral playback, the connected synthesizers were triggered for playback all at once. A GM instrument is literally equivalent to SIXTEEN synthesizers of old! A General MIDI instrument can transmit or receive up to 16 simultaneous MIDI channels through a single MIDI cable receptacle. Each channel can be assigned any one of the 128 GM sounds, except for MIDI channel 10, which is reserved for the Drum Kit.

24 Voice Polyphony
This is the number of actual voices (not necessarily notes) that can be played simultaneously. What's a "voice? Although I have grossly oversimplified this, the explanation still sounds a bit technical, so hang in there. When you play a note on a MIDI instrument, you trigger an internal circuit called a tone oscillator. Each tone oscillator produces a single "voice" (a sound). So, if you play a single note on a MIDI instrument, you are using a single voice, right? Well, sometimes. You see, there are some instrument sounds that actually use more than one tone oscillator to produce a particular sound. For example, some of the fuller, lush sounds on a synthesizer may use 2 or more oscillators (per note) to achieve that fullness. Let's see if you followed all that. If I play a 3-note chord on my MIDI instrument, and I am using an instrument sound that uses one oscillator per note, how many voices have I used up? The answer is, three voices. Now, if I play a three note chord, and I am using an instrument sound that uses two oscillators per note, how many voices are being used? The answer is, six voices. You can see that if a feature listed on a MIDI instrument is stated as "24-Note Polyphony," it is only correct if the sounds you use are triggering a single tone oscillator per note. The most accurate way for a manufacturer to state their instrument's polyphony is by voices, not notes i.e.: "24-Voice polyphony."

The Standard Drum Kit For General MIDI
There are 47 drum sounds assigned to universally specific MIDI note positions (like the keys on a synthesizer keyboard). The drums sounds are always accessed via MIDI channel 10 on a General MIDI instrument. Channel 10, therefore is designated as the "drum channel," and channels 1-9 and 11-16 are designated as "melodic channels" for use with the standard 128 GM sounds described previously.

General MIDI - Your Link To Compatibility With The Rest Of The World

So why is GM important? Predictable playback behavior is the primary reason. This alone makes GM extremely worthwhile in what can otherwise be a rather unpredictable environment. With a GM compatible instrument you have an organized, industry-standard set of sounds to choose from, and it will be compatible with any commercial MIDI songfiles you may purchase. You will also be compatible with your peers (since they, too, will most likely have a GM instrument).  Most software programs default to the GM sound list when you start up the software. This allows you to bypass the need for you to create a custom sound list yourself. Finally, you will be less likely to become distracted from your creative process when working in the General MIDI mode, since it is so simple to choose instrument sounds from a preset sound list.

The MIDI musician has a safety net that had not existed before the introduction of General MIDI. The benefits of GM extend well beyond the individual user. Now, if you compose music using the GM instrument set, you can be confident that your MIDI songs can be enjoyed by anyone else who owns a General MIDI compatible instrument. Prior to GM, a MIDI songfile would often prove useless to the recipient because of the wide variance of instrument assignments between different makes and models of MIDI instruments.

The cooperative effort among manufacturers whose instruments support the General MIDI standard has catapulted the usefulness of MIDI into the mainstream of musical creativity. This is the closest we have come to a turn-key system for the musician. At the GM level, the technology is not nearly as intimidating as it once was and allows newcomers to become productive quickly, without having to learn a lot of intrinsic MIDI details.

Does this mean that general MIDI is the perfect solution for musicians using MIDI? In a word, no - but it does make the technology accessible to nearly anyone! At the very least, you don't have to waste time fussing with drum key and instrument assignments every time you just want to play someone else's MIDI composition! In its basic form, GM is easy and simple to use.

But, what if you want to change the instrument settings? Or transpose the song? Add a new instrumental part? Change tempo? Of course, you can still manipulate a MIDI song in any way you want. You still have the freedom to customize any songfile for your particular tastes or application. General MIDI is simply a convenient starting point.

As your MIDI skill and knowledge increases, you may want to experiment a bit. With a little imagination, you can accomplish amazing musical feats within the preset limits of the GM standard. Although there are 128 instruments sounds to choose from, some of these sounds intentionally played outside of their normal range, can make viable substitutes for other instruments not included in the basic sound set. This way, you effectively expand your instrument options.

For instance, a clarinet sound transposed into a higher register, can have an exotic flute-like sound. Assigning a tuba sound to a higher-pitched part can sub for a baritone, and so on. Common arranging practices, such as doubling instrumental parts, has never been easier. Just copy, paste, and assign a sound from your instrument list!

You can have a lot of  fun finding new timbres by experimenting with instrument combinations and creative harmonies. Orchestra conductors could only dream of these capabilities a few years ago. You, with your desktop computer and your MIDI instrument, can try out new orchestrations in a matter of a few minutes just by clicking on different instrument selections!

NOTE: Most MIDI instruments you purchase today have many, many more sounds to choose from than just the basic 128 GM sounds. To access these additional sounds, you must be using software that either allows you to create your own custom soundlists for your instrument, and/or allows you to load a soundlist for your instrument that has already been created.

The most widely used music recording software is manufactured by the Cakewalk software company (SONAR is their most current offering at the top-end). SONAR is the product most home-recordists use if they have a PC-based recording studio. If your MIDI keybaord is not GM-compatible, the Cakewalk recording software includes several ".ins" files (instrument definition files) for a variety of common MIDI instruments and keyboards. Cakewalk software also lets you load custom ".ins" files that are freely available for download from the Cakewalk software site (ftp://ftp.cakewalk.com/pub/InstrumentDefinitions/) and other locations on the internet (do a search for "cakewalk ins files" or "cakewalk instrument definitions"). If an ".ins" file exists for your particular MIDI instrument, download it and  follow the instructions included with your Cakewalk software to configure it for use. If an ".ins" file does not exist for your instrument yet, then you can create a custom ".ins" file yourself, or wait for someone else to do it for you and wait until they post  it for download (if your instrument is very new or not "mainstream popular", an ".ins" file may not exist yet - give it a month or two -someone else will likely already be working on one!).

Beyond General MIDI

In anticipation of greater demands from consumers, Roland and Yamaha developed "extensions" of General MIDI in their respective GS (general standard) and XG (extended general) MIDI instruments. These instruments are compatible with the GM standard, yet offer a variety of additional features, such as reverb/chorus effects and more instrument sounds over and above the basic GM specification.

Early in General MIDI's conception, Roland simultaneously developed both GM and GS specifications. Roland's GS extension was an integral part of their original GM instruments from the very beginning (you may notice advertised MIDI songfiles as being GM/GS compatible). Roland would have preferred that the GS specification was the one that was initially embraced by the industry, but the simpler, more basic GM standard prevailed. Why? It is rumored that there were lots of "political" reasons, but I believe it was more a question of practicality. General MIDI was less expensive to implement on a wide scale and was sufficient enough for the purpose for which it was intended to provide an uncomplicated set of guidelines for universal cross-brand MIDI compatibility. Stray too far from this basic concept, and you begin to lose its benefits -namely, its ease of use and organized format. This is why nearly all commercial MIDI songfiles are at least GM compatible, assuring that the song will play with the basic instrument sounds originally intended by the composer, no matter if the recipient plays the song on GM, GS, or XG instruments. If the file does contain GS or XG support, then owners of such instruments may hear additional instrument variations and/or reverb and chorus effects not normally found in a standard GM instrument, where the GS or XG messages are ignored. In any case, the song should play back correctly since all three of these formats use GM as their base reference. The idea here is to maintain compatibility.

Conclusion

With general MIDI you have a simplified, more convenient means of composing, recording, and playback of music using software and your computer. Thanks to GM, all musicians can share their compositions to a wide audience and have the peace of mind that their music will sound as they intended! I'll sum this up by recapping some of the main reasons for owning a general MIDI instrument...

• You will have a consistent industry standard set of sounds to choose from
  

• You will be compatible with any commercial MIDI songfiles you may purchase 
  

• You are assured of compatibility with your peers who will most likely own a GM instrument themselves
  

• Most software programs you purchase today, will default to the general MIDI sound list at start-up, so you won't have to create your own sound list
  

• You will spend more time making music instead of serving as a "MIDI Technician" for non-General MIDI instruments!

How To Tell If Your Instrument Is General MIDI Compatible

Look for one (or more) of the following logos, either stamped or painted on the instrument itself, or on the owner's manual that came with your instrument...

If one or more of these logos are present, then you have a General MIDI compatible instrument. If not, well... you may want to go shopping!

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