Very simple: The vocalist requires the Digitech FS 300 footswitch to be used effectively. Any other switch can work but for only one function only, and bypass is not one of them.
This 3 switch box allows you footswitch control of program up, Program down, Song list up, Song list down, and bypass. Ther is also a bypass parameter which can be set to momentary on, momentary off, or latching (Harmonies remain on or off after footswitch is depressed.)