A re-creation of the classic Ross compressor, with very low noise. Use the Sustain, Attack, and Level knobs to find your ideal tone. Sustain: To control the delaying time of compressing; Attack: To control the starting time of compressing effect; Level: To control the output level. The Attack is especially designed for Bass or high-output active pickup. True bypass design minimizes tone loss. Aluminum alloy casing with stove varnish finish. Powered by a 6FF22 9V battery or 9V DC power adapter (neither included).