Differential pulse-code modulation

Differential pulse-code modulation (DPCM) is a signal encoder that uses the baseline of pulse-code modulation (PCM) but adds some functionalities based on the prediction of the samples of the signal.

Applying one of these two processes, short-term redundancy (positive correlation of nearby values) of the signal is eliminated; compression ratios on the order of 2 to 4 can be achieved if differences are subsequently entropy coded because the entropy of the difference signal is much smaller than that of the original discrete signal treated as independent samples.

DPCM was invented by C. Chapin Cutler at Bell Labs in 1950; his patent includes both methods.

[1] The encoder performs the function of differentiation; a quantizer precedes the differencing of adjacent quantized samples; the decoder is an accumulator, which if correctly initialized exactly recovers the quantized signal.

When the quantizer is uniform, the decoder regenerates the differences implicitly, as in this simple diagram that Cutler showed: