A voice frequency (VF) or voice band is one of the frequencies, within part of the audio range, that is used for the transmission of speech. In telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz. It is for this reason that the band of the electromagnetic spectrumbetween 300 and 3000 Hz is also referred to as "voice frequency" (despite the fact that this part of the electromagnetic spectrum is rarely used to actually convey audio signals). The bandwidth allocated for a single voice-frequency transmission channel is usually 4 kHz, including guard bands, allowing a sample rate of 8 kHz to be used as the basis of the pulse code modulation system used for the digital PSTN.
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