Mixing : Basic Mixing : Signal Flow by Track Type

Signal Flow by Track Type
Pro Tools provides the following track types:
*   
*   
*   
*   
*   
*   
VCA Master (Pro Tools HD and Pro Tools with Complete Production Toolkit only)
Audio, Auxiliary Input, Master Fader, and Instrument tracks can route audio. MIDI and Instrument tracks can route MIDI data.
VCA Master tracks do not pass audio or MIDI data, but do affect controls on other tracks. See VCA Master Tracks.
Tracks can be identified in the Mix window by their Track Type icon.