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The MIDI Channels
Every instrument in your MIDI setup has to have a MIDI Channel number assigned to it so that you can specify which
instrument will respond to which data stream. There are sixteen MIDI channels available for you to use: 1 - 16. It is important to
note that the channels are not exclusive, meaning that more than one instrument can be configured to respond to the same MIDI
channel without having to worry about any sort of conflict. In this way you can "layer" MIDI instruments to create incredibly rich
sounds. For example, you could have two devices in a chain that are both responding to MIDI channel number 1. The first
device could be assigned a nice, fat piano sound, while the second device has a nice string ensemble. When you play notes on
the first device, those notes would be sent down the chain and the device set up to respond to the same channel would trigger
the same notes using the string ensemble. The two sounds would come out of your speakers as if they were a single
instrument. Layering instruments in this way gives you the ability to produce some very unique sounds without having to learn
how to create voices from scratch.
There are different MIDI MODES that each instrument can be set to that determines exactly how it responds to incoming MIDI
data streams. If an instrument is set to OMNI ON, a MIDI device will try to respond to what ever MIDI information comes into it
regardless of what MIDI channel it is set to. Some older MIDI devices must be set to MIDI channel 1 for OMNI ON to function
properly... this is not generally a limitation of newer MIDI devices. The second mode is OMNI OFF, which is the default for
most synthesizers. In the OMNI OFF mode a synth will only respond to a MIDI data stream that corresponds to the device's
MIDI channel. There are also two other modes that you must be aware of that affect the audio output of a MIDI device and work
in conjunction with the two OMNI modes. These two additional "Voice Assignment"modes are known as POLY and MONO. If a
MIDI device is set to OMNI OFF/POLY, then it will respond only to its specified MIDI channel and it will play as many voices as
it is capable of playing. A  Yamaha
DX7 II, for instance, can play up to 16 different notes at one time. So, you could
effectively play a sixteen note chord (if you had enough fingers). If you had 17 fingers, when you tried to play the 17th note,
the first note that you played would drop out to make room for the newer note. Some synths can only play as little as four
notes at a time, and some of the even older devices can only play one note at a time. These are known as MONOPHONIC (or
one voice) synthesizers. The corresponding MIDI MODE is known as MONO. If you set your synthesizer to OMNI ON/MONO,
then it will respond to all incoming MIDI data streams and only play one note at a time... not very practical, but can be useful in
situations where you need ambient background noise to create a subtle effect or for some sort of solo instrument.
Most newer MIDI devices available today are MULTI-TIMBRAL. Meaning that they can respond to multiple MIDI Channels, with each
channel having a different sound assigned to it. Roland’s Sound
Canvas is a good example of this. The little box has no keys as it was meant to be accessed from a MIDI controller such as
a Master
Keyboard.
The Sound Canvas can play 32 notes at once (another way to say it is 32 note polyphonic) and it can
respond to all 16 MIDI channels at the same time. Each MIDI channel can be assigned its own unique sound. Having a
Multi-timbral MIDI device is like having 16  keyboards in one little box. You can create a whole symphony on one of these
babies - until you run out of notes, that is! The Sound Canvas, however, as do many other multi-timbral devices, allows you
to chain multiple devices together so that you can effectively create a larger note
base to draw from when playing... any notes that would normally be dropped out would automatically be routed to the other
device. Two Sound Canvas’ hooked up in this way would create a 64 note polyphonic instrument.
Once you start adding new devices to your MIDI setup, you will quickly find yourself thinking "Sixteen MIDI Channels are not
enough!" Never fear... there is a way to control more that sixteen MIDI devices at one time, using more than the available 16
channels. Well, sort of.... the solution is a
MIDI Patch Bay.
It not only allows you a more sophisticated MIDI recording setup,
it opens up a whole new world of synth sound (patch) management.
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