The Dyna Comp is a compressor that lets you set a maximum output level and the sensitivity at which it kicks in. This device can produce that percussive, clicky sound on a clean guitar that you've heard on so many pop hits. It can also even out the volume of sustained tones for mellow lead work, Power: Single 9-volt battery or Dunlop ECB-003 AC Adapter - Controls: Footswitch toggles effect on/bypass (red LED indicates on) Output knob sets compressed (attenuated) output level Sensitivity knob sets compression ratio (highest sensitivity is maximum compression).