Compression is perhaps one of the most useful FX available to any guitarist who is interested in improving their sound. The purpose of the Compressor pedal is primarily to allow you to modify sustain and attack. Using classic variable gain techniques the Compressor will provide masses of clean sustain, which can enhance any playing style.
The Compressor pedal senses the level of the incoming guitar signal and, as the signal level decays, the gain of the internal circuitry is boosted to provide extra level, hence sustain. The attack control modifies the dynamic response of the guitar signal (the effect of plucking a string) and allows you to achieve a range of effects from rounded and mellow chord sustain to muted, percussive funk lines.
The Compressor also features an Emphasis control, which allows you to assign compression and target the frequencies you want to compress. This means that you can, for example, tighten up or compress your bass notes and let your treble notes ring out.