In the UK, often, and more properly called delta-sigma modulation. A type of PCM which differs from most other digital encoding schemes in that the signal, after being sampled at a fast rate, is encoded as the difference between successive levels, rather than as the absolute level of each sample. Delta modulation requires a very high sampling rate, usually around 700kHz, but the digital words need for each step contain one bit, whereas conventional PCM samples at only about 45kHz but requires 14-16 bit words. The “delta” phase of delta modulation involves taking the difference of the reconstructed signal and the incoming signal to adjust the output to minimize the quantization error; the “sigma” part involves the summation of the differences to reconstruct the original signal, although there are a number of variant algorithms based on this basic theme. The reason for the popularity of delta modulation-type converters is the inherent linearity of the process. See also ADPCM.