Output (formerly called 'instrument' in Metro versions prior to 6.0.8) A MIDI output is a configuration associated with a specific MIDI channel (or channels) and output port (or ports). An audio output is a configuration created in the Modify Outputs and Busses dialog box that associates to an audio port. A track can be assigned one or more outputs. The track type (audio, MIDI or video) is determined by that assignment. Each output has a fader in the Mixer window (formerly called the Instruments window) that can be used for mixing and automation.