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Old 2005-03-11, 06:38 AM
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rherron rherron is offline
Columbia, SC
Join Date: Dec 2004
Re: What does PCM stand for?

PCM, Pulse Code Modulation (developed in 1939), is a standard method for digitizing analog audio signals. This format is an uncompressed, raw bit stream, linear (transmitted in a linear series meaning that the stream of the signal is sequential rather than random and the amplitude of both the of the input signal and output signal remain at a fixed ratio and a sinusoidal wave input signal will result in a sinusoidal wave output signal at the same frequency), signed two's complement, fixed point encoded data file. A PCM encoder (ADC) may sample analog sound from 8,000 times per second (8 KHz) and use 8-bits to represent each sample, is usually utilized at 44.1 KHz and 16-bit resolution to match CD Audio standards, and can encode at 96 KHz and 24-bit (approximate). The procedure uses only two alternating pulse values (1 and 0) duplicating binary code. This codec creates a raw (RAW) data file (no header or footer information describing sample rate, sample resolution, monaural or stereo) and gives us only 256 possible amplitude values (based on 8-bit binary numbering). When the codec is set to sample at the Audio CD level at 44.1 KHZ sample rate (44,100 samples per second), with 16-bit resolution per sample (65,536 possible amplitude levels), this results in a file that requires 1,411 Kbps (kilobits per second, or 1.4MB) bit rate for representation / playback of one second of stereo music.

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