DPCM - technical definition

A voice encoding technique used to express analog signals in digital format. DPCM is more efficient than PCM in terms of bandwidth utilization, as only the quantized differences in signal values are encoded and transmitted. DPCM compares two successive analog amplitude values, quantizes and encodes the difference, and transmits the differential value.As it can be assumed that the change, or differential, in the voice signal occurs relatively gradually, relatively few bits can be used to represent each sample. DPCM will work with various numbers of bits, but a 4-bit approach generally is used in this technique, which yields a 2:1 (2-to-1) compression ratio, when compared to 8-bit PCM. At 32 kbps, DPCM generally provides voice quality comparable to that of PCM at 64 kbps, although distortion can result if the signal varies significantly from one sample to another.A modem transmission, for example, is characterized by amplitude (i.e., volume) and frequency (i.e., pitch, or tone) levels that vary abruptly.Although DPCM is unusual, a variation known as adaptive differential pulse code modulation (ADPCM) is commonly used. See also ADPCM, analog, bandwidth, compression, digital, encode, modem, modulation, PCM, and quantize.