Abbreviation for Adaptive Differential (or Delta) Pulse Code Modulation. A type of CODEC used in digital recording, where it is a version of Pulse Code Modulation (PCM) that encodes primarily the differences between the current and the previous value of adjacent samples. This reduces the number of bits required per sample by approximately 25% compared to PCM. ADPCM is “adaptive” because it varies the size (in bits) of a digital recording to allow further reduction of the necessary bandwidth in relation to the signal-to-noise ratio.
ADPCM is not a single standard. There are several different versions in common use. Many MP3 players use a form of ADPCM for their voice-recording feature.