A hardware or software unit that compresses the audio signal. Various effects made by a compressor depend on the particular settings of its parameters. A typical parameters of a compressor are: threshold, ratio, attack and release times, and make-up gain.

There a few famous compressors, which have constituted a model for many reproductions for decades, for example: Empirical Labs's Distressor, or UREI's 1176 Peak Limiter.