Product Details Compression and Release controls Output control to compensate for heavy compression True bypass, analog design All-metal chassis construction Powered by a 9V battery or 9V DC supply (not included) The Ampeg Opto Comp is an analog optical compressor designed to control the dynamic range of your sound without squashing it. Particularly useful for slap and aggressive pick players, the Opto Comp will control your dynamics while preserving your original tone. The Opto Comp is an optical compressor which is a type of analog compression that has a softer attack and release. Many compressors have a harsher compression and characteristically quacky tone which some find desirable, but it's not for everyone. The Opto Comp won't colour your tone in any dramatic way so it's ideal for players who want to take control of their dynamics but don't want to lose the tone they've crafted. With a simple control set-up of Compression, Release, and Output Level, you can shape the compression to suit your needs. Whether you want to rein in some of the looseness in your sound or you play an aggressive slap or picked style and you need to ensure your sound is consistent, you can set the Opto Comp to meet your needs.