ADPCM

A form of pulse code modulation (PCM) that produces a digital signal with a lower bit-rate than standard PCM. ADPCM produces a lower bit-rate by recording only the difference between samples and adjusting the coding scale dynamically to accommodate large and small differences. Some computer applications use ADPCM to digitize voice signals so that audio and data can be transmitted simultaneously over a digital facility normally used for one or the other. It's one of those boring but important concepts ;-)