dancehall posted:

Depends on the pedal it's used with. It can fade between dry/wet signal, control modulation speed... basically anything that a knob can do can be made controllable by an expression pedal.

edit: don't know how much you understand.... an expression pedal by itself doesn't do anything, it's like a MIDI controller keyboard in that respect. You have to use it with an exp-pedal-controllable effect.