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Collaboration, Voice & AV · Foundational

Pulse Code Modulation (PCM)

The method of digitizing analog audio by sampling, quantizing and encoding the signal as binary values.

Definition

PCM converts an analog waveform into digital form in three steps: sampling at a fixed rate, quantizing each sample to the nearest of a set of levels, and encoding the level as a binary word. Telephone-quality PCM samples at 8000 Hz with 8-bit companded values, producing 64 kbps, which is the G.711 codec. Higher-fidelity audio PCM, such as 48 kHz at 24 bits, is used in professional AV and Dante networks.

Example

G.711 is PCM at 8 kHz and 8 bits per sample, giving 64 kbps.

Exam tip

Know the order sample, quantize, encode, and that quantization introduces noise that companding reduces for speech.

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