The MXR Dyna Comp is a compressor pedal designed for guitar players.
It's a signal limiting processor, which varies its gain so the output signal that you set remains constant. This compression circuit is coupled with a sensitivity control. This combination of controls made the Dyna Comp one of the most popular guitar compressors ever. For overdrive or clean sounds, you get increased sustain and superb tone.
MXR M102 Dyna Comp Compressor Pedal Features