pulse code modulation system造句

In telephony, the usable channel is usually 4 kHz, including guard bands, allowing a sampling rate of 8 kHz to be used as the basis of the pulse code modulation system used for the digital PSTN . Per the Nyquist Shannon sampling theorem, the sampling frequency ( 8 kHz ) must be at least twice the highest component of the voice frequency via appropriate filtering prior to sampling at discrete times ( 4 kHz ) for effective reconstruction of the voice signal.
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