differential pulse code modulation (DPCM)
Differential pulse code modulation (DPCM) is a lossy coding method in which the difference between two successive samples is encoded. In this process, a predictor is calculated from past sample values, which is subtracted from the current sample value and its prediction error is transmitted. On the receiving side, a predictor is also calculated from past reconstructed samples and corrected with the transmitted prediction error.
In contrast to DPCM, Adaptive Delta Pulse CodeModulation( ADPCM) also uses prediction, but adapts the predictive signal to the input signal, allowing better prediction. The method is used in speech digitization and has the advantage that far fewer bits are needed to encode a sample, resulting in a substantial reduction in data. With this method, errors can occur if there are large differences between adjacent samples. These can be corrected by sampling the full amplitude value again after a few samples instead of the difference value.
The disadvantage of this method is that a level loss of 6 dB/ octave occurs, causing the signal-to- noise ratio( SNR) to drop by 6 dB/octave and high tones to be transmitted more poorly.