Mixing : Basic Mixing : Inserts : Track Output Format and Plug‑Ins

Track Output Format and Plug‑Ins
Pro Tools supports mono, multi-mono, stereo, and multichannel plug-ins (Pro Tools HD with Surround Mixer only).
Because inserts process in series, changing the plug-in format can alter the channel format. For example, inserting a mono-to-stereo plug-in on a mono Auxiliary Input changes the signal path from that plug-in through the rest of the track. This restricts all hardware inserts or plug-ins after the stereo plug-in to be stereo-in/stereo-out plug-ins (or the supported multichannel format).