Pulse-code Modulation - Limitations

Limitations

There are potential sources of impairment implicit in any PCM system:

• Choosing a discrete value that is near but not exactly at the analog signal level for each sample leads to quantization error.
• Between samples no measurement of the signal is made; the sampling theorem guarantees non-ambiguous representation and recovery of the signal only if it has no energy at frequency f_s/2 or higher (one half the sampling frequency, known as the Nyquist frequency); higher frequencies will generally not be correctly represented or recovered.
• As samples are dependent on time, an accurate clock is required for accurate reproduction. If either the encoding or decoding clock is not stable, its frequency drift will directly affect the output quality of the device.