Pulse-code
modulation (PCM) is a
digital representation of an analog
signal where the magnitude of the signal is
sampled regularly at uniform intervals, then
quantized to a series of symbols in a digital (usually
binary) code. PCM has been used in digital
telephone systems and is also the standard form for
digital audio in
computers and the
compact disc red book format. It is also standard in
digital video, for example, using
ITU-R BT.601. However, straight PCM is not typically used for video in consumer applications such as
DVD or
DVR because it requires too high a
bit rate (PCM audio is supported by the DVD standard but rarely used). Instead, compressed variants of PCM are normally employed. However, many
Blu-ray Disc and
HD-DVD movies use uncompressed PCM for audio. Very frequently, PCM encoding facilitates digital transmission from one point to another (within a given system, or geographically) in
serial form.
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Modulation in which a
signal is sampled, and the magnitude (with respect to a fixed reference) of each sample is quantized and digitized for
transmission over a common
transmission medium. (
188 ) Note 1: In conventional PCM, before being digitized, the
analog data may be processed (e.g., compressed), but once digitized, the PCM signal is not subjected to further processing (e.g.,
digital compaction) before being multiplexed into the aggregate
data stream. Note 2: PCM
pulse trains may be interleaved with pulse trains from other channels.
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