What Is PCM

As covered in Chapter 1, PCM converts analog sound into digital form by sampling the analog sound 8000 times per second and converting each sample into a numeric code. The Nyquist theorem states that if you sample an analog signal at twice the rate of the highest frequency of interest, you can accurately reconstruct that signal back into its analog form. Because most speech content is below 4000 Hz (4 kHz), a sampling rate of 8000 times per second (125 ms between samples) is required.

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