Here's what MXR say about the M102 Dyna Comp Compressor:
The Dyna Comp Compressor can tighten up your signal, add rich sustain, or create the percussive and clicky sound heard on numerous hit records.
The Dyna Comp Compressor is one of the most popular compressors of all time. Whether you want to tighten up your signal, add rich sustain, or create the percussive and clicky sound heard on numerous hit records, this pedal is straightforward and easy to use. For these reasons, the Dyna Comp Compressor has been the secret weapon on countless pedalboards for years.
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).