A Beginner's Guide To MIDI

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Let's suppose that the first receiving module in the chain is set to play a piano sound, and the second is set to play a brass sound. It would be helpful if the devices could distinguish between information which is targetted at each other, so that the piano sound could be played independently of the brass.
This is done through the use of M.I.D.I. Channels. Every instruction transmitted by the mother keyboard is identified as being on a particular M.I.D.I. Channel. Meanwhile the receiving modules are set to respond on their own M.I.D.I. Channels (these can be the same if desired). When an instruction arives at the module, the device will only follow the instruction if the message's transmit channel (TX) corresponds to its receive channel (RX).

There are 16 M.I.D.I. channels within MIDI protocol, however, some hardware devices allow multiple streams of M.I.D.I. data, and the affect of hundreds of M.I.D.I. channels can be achieved. Be aware though that the number of actual channels is still just 16 - the hardware (in combination with the Software) simply redirects data to more than one M.I.D.I. This allows (for instance) two devices to each receive a full compliment of 16 channels, giving the impression of 32 channels at work, but no instrument can be set to receive on M.I.D.I. channel 17!