PCM
Communications Systems Glossary
Communications Systems — Line Coding — PCM
Information on PCM
Pulse-code modulation is similar to pulse-position modulation (PPM) in that the received information is not determined by the shape of the pulse, but has the additional advantage that the precise location of the pulse is not important either. The analogue signals are first sampled using pulse amplitude modulation. The pulse amplitude modulation pulses are then encoded into a binary code that is transmitted as a digital stream. At the receiver these PCM codes are decoded into pulse amplitude modulation (PAM) pulses that are then used to reconstruct the analogue waveform. In adaptive differential pulse-code modulation (ADPCM), the binary number that is transmitted is not the number that corresponds to the actual voltage level, but rather the difference between the current sample value and the last. The difference values have a smaller dynamic range and compression (of the order of one-half) results).
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