7. Waveform Coders

In Chap. 6, we saw that there exist a wide variety of speech encoding/ decoding algorithms with varying capabilities in terms of quality of decoded speech, input sampling rate, and output data rate. One way to broadly classify speech coders is based on whether the encoding algorithm makes an attempt to represent the original waveform in some form or whether the encoded data purely consists of specific parameters that try to model the characteristics of human speech for a particular speech segment and speaker. The former category of speech coders is known as Waveform Coders. Waveform coders are immensely popular in embedded applications due to their low cost, low computational resource usage, and high speech quality, even though they do not provide as high a compression ratio as the latter category of speech coders known as Voice Coders. In this chapter, different types of quantization will be discussed and correlated with various popular Waveform Coders. A special focus will be on those coders that have been standardized by the International Telecommunications Union: G.711, G.722, and G.726A.