A compressor pedal is an effect pedal that controls the dynamic range of an instrument, making the soft parts louder and the loud parts softer. It reduces the amount of dynamic range of an audio signal, making quiet sounds louder and loud sounds quieter. The pedal protects against excessive peaks in the signal and "smothers" the sound a bit more, gluing different notes together and making it sound more "produced" and professional. It is used to even out the dynamics of a musical performance, resulting in a more balanced sound. A compressor pedal can also add sustain, which is useful for solos.

Most compressor pedals have a "sustain" control and a "level" control. The sustain control adjusts the amount of compression, while the level control adjusts the overall volume of the effect. Depending on the compressor, it may also have attack and tone controls. The pedal is usually placed at the beginning of the signal chain, just before or after other effects pedals.

In summary, a compressor pedal is an effect pedal that reduces the dynamic range of an audio signal, making quiet sounds louder and loud sounds quieter. It is used to even out the dynamics of a musical performance, resulting in a more balanced sound, and can also add sustain. The pedal is usually placed at the beginning of the signal chain, just before or after other effects pedals.