Korpa 
The Bass Compressor provides recording-quality compression with Constant Headroom Technology™ and true bypass switching for keeping your low end tight and clean.
This pedal can be powered by a 9-volt battery, a Dunlop ECB003 9-volt adapter, or the DC Brick™, Iso-Brick™, and Mini Iso-Brick™ power supplies (not included).
The Long Story
Take your favorite studio compressor to the stage with the MXR Bass Compressor. A complete array of controls—Attack, Release, Ratio, Input, and Output—makes it easy to fine-tune your sound, from subtle peak limiting to hard squashed compression effects. Its CHT™ Constant Headroom Technology gives you plenty of headroom and clear performance. This totally transparent compressor allows your full dynamic range to shine through until your signal reaches the compression threshold, which is indicated by the ten, highly visible gain-reduction status LEDs. It's all packed into a durable, lightweight aluminum-housing pedal that's the size of a Phase 90.