A technique for converting analog sound, such as speech, into binary digital information by frequently sampling the sound and expressing its modulation in binary form.
Adaptive Differential Pulse-Code Modulation (ADPCM) codecs convert analog signals into digital information by quantizing the differences between the actual analog signal and a predicted signal.
The result is that analog signals encoded into files using ADPCM have a smaller size than many other formats. ADPCM enables speech information to be compressed into small files for storage and transmission.
Personal Communications Services (PCS) cellular telephony systems use a 32-Kbps ADPCM coding system to provide the same quality of voice communication that is available in wired telephone networks. This standard was developed by the International Telecommunication Union (ITU) and is known as G.721.
See examples of this kind of device: RAD - KM-2000M-KVC.1M/E - 2-channel Pcm/adpcm Voice Module, 2/4-wire E&m