Electro-Harmonix  Bass Preacher Bass Compressor/Sustainer Pedal Compact compressor designed especially for bass guitar.Input sensitivity ranges from -10 dBu to +2 dBu making it a perfect fit for both passive and active basses of varying output levels. Maximum gain reduction of 21 dB, with enough make-up gain to return your signal to full volume at maximum sustain (compression) Attack toggle switch changes the timing of the onset of compression and provides three selectable settings: Fast, Medium and Slow True bypass for maximum signal path integrity when in bypass mode 9-Volt battery includedOptional EHX9.6DC-200mA power supply available