In MIDI, a logical division of a physical MIDI cable, somewhat analogous to the way that a cable TV system carries multiple program channels on one cable.The MIDI standard divides each cable into 16 logical channels, and nearly every message type contains a channel number that specifies what channel it applies to. The use of channels and MIDI thru (or a splitter box) allows multiple synths or devices to be connected to the same physical MIDI line. Each synth or other receiving device can receive data on one or more channels. Usually, devices have a setup or configuration parameter that allows the user to specify what channel or channels they should transmit or receive MIDI messages on. The performer must take care not to assign the same channel on the same cable to two different devices, or else confusion will almost certainly ensue.

In the early days of MIDI, before multitimbral synths existed, most synths that received MIDI data received only on a single channel (unless in omni mode). Keyboards capable of setting up splits could then be programmed to transmit on different channels to control multiple synths from different regions of the keyboard.When multitimbral synths arrived, the concept was extended so that (in most cases) the transmitting MIDI device sees the receiving device as a number of synths in one box, each capable of playing a different patch under control of a different channel. The number of channels needed in a complex setup increased greatly. (It is not uncommon now to find a synth that uses all 16 channels.) This development was unanticipated by the original MIDI standard, and the result has been the rising popularity of multi-output MIDI interfaces.

Drum machines are, by convention, usually assigned to channel 10. Other than that, there is no rule for which devices should use which channels. Some very old synths and devices can send or receive only on channel 1.

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