Page 204 - Asterisk™: The Future of Telephony

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Figure 7-9. Five-bit plotted PCM signal
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Figure 7-10. Waveform delineated from five-bit PCM
Nyquist’s Theorem
So how much sampling is enough? That very same question was considered in the 1920s
by an electrical engineer (and AT&T/Bell employee) named Harry Nyquist. Nyquist’s
Theorem states: “When sampling a signal, the sampling frequency must be greater than
twice the bandwidth of the input signal in order to be able to reconstruct the original
perfectly from the sampled version.” *

176 | Chapter 7: Understanding Telephony