“If I could determine what there is in the very rapidly changing complex speech wave that corresponds to the simple motion of the lips and tongue, if I could then analyze speech for these quantities, I would have a set of speech defining signals that could be handled as low frequency telegraph currents with resulting advantages of secrecy, and more telephone channels in the same frequency space as well as a basic understanding of the carrier nature of speech by which the lip reader interprets speech from simple motions.”
–Homer Dudley, 1935
If we think, for the moment, of speech as being a mode of transmitting word messages, and telegraphy as simply another mode of performing the same action, this immediately allows us to conclude that the intrinsic information rate of speech is exactly the same as that of a telegraph signal generating words at the same average rate. Speech, however, conveys emphasis, emotion, personality, etc., and we still don't know how much bandwidth is needed to transmit these kinds of information.
In the following sections, we begin with some further historical background on speech communication.
Perhaps the earliest network for speech communication at long distances was a system that we'll call the “stentorian network,” which was used by the ancient Greeks. ...