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PCM - Pulse Code Modulation

 

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DSD Glossary Entry

Bitrate Glossary Entry

 

 

Pulse Code Modulation, or PCM for short is the format that almost all digital sound recordings are made up from.

PCM is a combination of a few different parameters of a recording. Namely, Bit Depth, Sample Rate and Number of Channels.
A standard CD for example, in it's uncompressed state has a Bit Depth of 16 Bits, a Sample Rate of 44,100 Samples per Second and (usually) Two Channels of audio information.

 

A PCM stream is formulated by taking a sample of an analogue waveform (musical signal) a certain number of times per second, and then plotting where at the time of the sample, the signal is in reference to 0.

 

 


The Bit Depth is the number of possible plots on the Y axis. 16 Bits give a maximum number of different values of 65,535.

 

Higher Resolution audio data is the same principle, but generally with a larger bit depth of 24 or even 32, and a sample rate of between 96,000 or even up to 384,000 samples per second.

This makes for a much more accurate musical signal as it reduces quantization error (an error introduced where the chip must try to 'guess' the information between samples). However requires much more bandwidth and memory, as well as higher quality DACs and faster clocks.
For example, a CD with a sample rate of 44.1KHz and 16Bit bit depth is 16x44,100x2 (for stereo) means 1,411,200bits per second (1,411.2Kbps or 1.4Mbps) whereas a High Res recording at 24bit 96K samples per second is a whopping 4,608,000bits per second (4.6Mbps).

 

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