ADPCM
Adaptive Differential Pulse Code Modulation
A slightly more efficient method than PCM (Pulse Code Modulation) for encoding analog sounds to digital form. ADPCM comes in more than one flavor: IMA's ADPCM is used on the Sony MiniDisc; Microsoft's ADPCM is used by Windows. Many MP3 players use a form of ADPCM for their voice-recording feature.