The Bit Mixer requires a 9-18V DC center negative power supply. Typically you will use a standard 9V DC pedal power supply, which give a headroom of about +10 dBu (7.2 Vp-p). You can use a 12V or 18V power supply for more headroom, or if you have an extra power outlet.
Each Bit Mixer channel goes from off at minimum to unity gain at maximum.