Abstract
Waveform coding is the type of speech digitization used in the public switched (wireline) telephony network. Waveform coding techniques describe the waveform’ s instantaneous behavior. This means that the waveform does not have to be speech; in fact it can be analog data or a signaling tone. The simple process of sampling and quantizing a waveform might be called “brute force coding.” It is done independently of any special characteristics the input may exhibit. Such coding actually is called linear pulse-code modulation (PCM). This chapter begins with a discussion of PCM, but then shows that by making use of certain special characteristics of speech, the required bit rate can be reduced significantly below the 96 kb/s or more of linear PCM, and even below the 64 kb/s of standard telephony PCM. The term PCM refers to the use of a specific set of mles for transforming a waveform into a stream of digits, and vice versa. To clarify the concept, however, the first point to be made is that PCM is coding, but it is not the modulation of a carrier. Modulation usually refers to an alteration of a periodic function (often a radio-frequency sine wave) to cause it to convey intelligence. This alteration may be a change in amplitude or frequency or phase of the sine wave. These are the ways in which a carrier can be modulated. The PCM process, in contrast, is a coding technique. The resulting stream of ones and zeros can be used to modulate a carrier in any of the ways mentioned here, or special combinations of them.
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Keiser, B.E., Strange, E. (1995). Waveform Coding. In: Digital Telephony and Network Integration. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-1787-0_3
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