35. MIDI Channels
MIDI instruments are designed so that they respond to incoming messages according to a specification known as the MIDI channel. A MIDI channel is a numerical designation associated with MIDI messages and instruments contained in a MIDI system. When, for instance, a MIDI message is sent from a keyboard controller to MIDI sound-producing instruments more than information about what notes to play and how loudly to play them is sent.
MIDI messages also carry numerical designations from 1 to 16, indicating their MIDI channel. Instruments in a MIDI system are also labeled with (set to) specific channel designations ranging from 1 to 16. If the MIDI channel of the MIDI message corresponds with the MIDI channel setting of the instrument, that instrument will respond. If the message is on a channel different from the channel the instrument has been set to, the instrument will not respond.
Almost all instruments allow the user to select on which channel MIDI messages are transmitted and on which channel MIDI messages are received.
Example 35-1: Only the sound module on channel 7 responds, even though all three modules receive MIDI messages.
The concept of channel, therefore, enables the user to route MIDI messages to specific instruments in the system. If, for instance, a user wants to route a certain group of note-on messages (or other performance directives) to a specific instrument, all that needs to be done is to match the channel on which the MIDI data is transmitted to the channel on which an instrument has been set.
An important point to remember is that MIDI messages generally go to all instruments in the MIDI system. Even an instrument set on a single channel will probably receive MIDI messages on other channels as well. MIDI instruments are sophisticated enough to ignore messages on MIDI channels other than the one to which they have been set.