(1) In the analog world, a method for improving audio reproduction by altering the dynamic range of the signals. On outgoing transmission, it raises the amplitude of weak signals and lowers the amplitude of strong signals. On incoming transmission, it restores the signal to its original form. Such techniques are used in dbx and Dolby noise reduction, AM, FM and SSB radio as well as in voice and musical instrument amplification to reduce feedback. See codec.

(2) In the digital world, a compression technique used in pulse code modulation (PCM). It reduces the number of bits used to represent digital voice samples in the loudest parts of the conversation. See mu-Law, A-Law and codec.