CS400 effector with compressor/sustainer function and four adjustment knobs. I've only tested it a few times at home. From the manufacturer's website: ■ Guitar effector ■ Compressor/Sustainer ■ Power supply: 9V battery or adapter (sold separately) ～From the manufacturer's website～ ■ Smooth compression and endless sustain. Compresses boosted low signals without degrading the original sound. ■ Level, Tone, Attack, and Sustain controllers enable precise sound shaping. Thank you for looking.