midi for newbs - channelThink of a "channel" as a guy playing an instrument.
At any given time, a guy can pick up only one instrument.
He can play tons of notes at once on the instrument.
He can swap instruments any time he wants.
But only one instrument at a time.
A channel has an assigned sound. Defaulting to drums on channel 10 and piano on the other 15. Assigning a sound to a channel is called a "program change".
Midi defines 128 standard melodic sounds and about 61 standard drum notes. These are only the standard ones. In practice, this is way too few available instruments for everyone in the whole world to limit themselves to. So you usually end up using custom ones. And mapping these custom instruments back to the closest standard one when giving the song to somebody else.
You can have as many melodic and percussive instruments as you want. But per device, only 15 melodic instruments can be used at a given instant on the melodic channels. Plus channel 10 of drums sounds. Drum channels are weird with a sound per note as no pitch is needed. For melodic sounds, one sound per channel.
If you want more simultaneous sounds, you need more sound module devices. Most of the time, you've got a couple of em. So you can have 30 (plus 2 drumsets) with 2 devices. Or 45 sounds (plus 3 drumsets) at once with 3 devices. If that's not plenty, just get more devices.
Plus, you can switch off a channel to another sound at any time. (With a "program change" control message.) So within a bar of music, you could have a zillion instruments playing.
However, doing program changes can sometimes cause an audible bzzzt. And lots of program change events can make it hard to keep your music easy to understand.
WHY all these wierd numbered limits?Well, MIDI was designed in the 1980s when computers were weak... (And MUCH simpler. And I was a younger man...) That's all the explanation you get for now. Sorry.
next: note home