(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.
Referring to the twin processes of compression and decompression as used in the conversion of a voice signal from analog to digital format and then converting the signal back from digital to analog. The ITU-T G.711 Recommendation for pulse code modulation (PCM) specifies both.