TABLE OF CONTENTS Chapters 1, 2 and 3 described the foundations of speech signal processing the characteristics of audio signals in general, methods of handling and processing them and the features of speech as produced and understood by humans. In particular we have covered some basic MATLAB methods for handling speech and audio which we will build upon in this chapter as we embark upon an exploration of the handling of speech signals in more depth.
This chapter will consider typical speech handling in terms of speech coding and compression (rather than in terms of speech classification and recognition, which often use similar techniques but are higher level in nature). We will first consider quantisation of speech, which assumes that speech is simply a general audio waveform (i.e. it does not incorporate any knowledge of the characteristics of speech).
Knowledge of speech features and characteristics allows for parameterisation of the speech signal, and then source filter modelling which will be considered in turn. Perhaps the pinnacle of achievement in these approaches is the CELP (Codebook Excited Linear Prediction) speech compression techniques, which will be discussed in the final section.
Speech compression, or codec systems, are classified according to what they compress: speech, or general audio, how well they compress this, and how well they perform in terms of quality or intelligibility (which were differentiated and measured in Section 3.3.1). To aid in this classification, there is a general agreement on terms used to describe the...
