The MXR design team took a classic recording studio fixture and put it into a pedal board friendly box. A complete array of controls; input, output, ratio, release and attack so you can fine tune your compression level with visual feedback from a bright gain-reduction LED status meter. CHT Constant Headroom Technology provides tons of head-room for clear, clean performance. True hardwire bypass. Powered by a 9 volt battery or AC adaptor (ECB003).