Introduction to Data Communications
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23. Voice Channel Communications

The voice channel or dial-up line is the line from our telephone/modem to the outside world.

As the name implies "voice" channel is designed to carry human speech over the telephone wires.

23a. Voice Channel Specification

Human speech covers the frequency range of 100 to 7000 Hz (hertz) but research has shown that the intelligence part of human speech is carried in the 300 - 3400 Hz range. This range is called the Voice Band.

The Voice Channel has a range of 0 to 4 kHz (4000 Hz). The area from 3400 to 4000 Hz is used for system control and is called Out of Band Signalling.

23b. Voice Channel Constraints

Due to the limited Bandwidth (BW) of the Voice Channel (0-4 kHz), we are limited to the amount of data that we can pass through the Voice Channel. The Nyquist Theorem addresses this limitation.

Introduction to Data Communications
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