Introduction to Pro Tools : Pro Tools Concepts : Pro Tools Sessions : Channel

Channel
The term channel is used to describe several related components of a Pro Tools system.
The first example of channel refers to a physical input or output of your Pro Tools system. For example, HD I/O provides up to 16 channels of audio input and output to an Avid HDX, Pro Tools|HD, or HD Native system, while the Mbox Pro audio interface provides up to eight inputs and eight outputs.
The second use of the term channel refers to a channel strip in the Pro Tools Mix window. Each track in a Pro Tools session has a corresponding channel strip in the Mix window.
Audio and MIDI channel strips have similar controls, but those controls have slightly different effects. For example, audio, Auxiliary Input, and Instrument track channel strip faders control the output gain to the mix bus for that channel, while MIDI channel strip faders send MIDI volume data (MIDI controller 7) to the selected MIDI instrument.
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The term “MIDI channel” also describes a separate aspect of MIDI operation. See MIDI.