ABSTRACT
CONTENTS 11.1 Speech Coding: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 11.2 Waveform Codecs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 11.3 Speech Vocoders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 11.4 Hybrid Codecs: Analysis by Synthesis (AbS) . . . . . . . . . . . . . . . . . . . . 270 11.5 LPC Parameters for Speech Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 11.6 Speech Coding Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 11.7 Comparison of Speech Coding Standards . . . . . . . . . . . . . . . . . . . . . . . 278 11.8 Speech Coding: Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 11.9 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
11.1 Speech Coding: Introduction Previously in Chapter 7 coding focused on general and wideband audio codecs such as MPEG1 audio layer3 (MP3). This chapter focuses on codecs specifically designed for speech coding. These codecs have a long history of standardisation and have in a general sense improved in quality (for equivalent bandwidth) over this time. Speech coding techniques are specifically designed for speech signals. They are therefore suboptimal for music and other general audio applications, i.e., using a mobile phone to listen to music over a GSM line is not a good idea.
