ABSTRACT
Speech coding has found a diverse range of application such as cellular telephony, voice mail, multimedia messaging, digital answering machines, packet telephony, audio-visual teleconferencing, and, of course, many other applications in the Internet arena. Principal coding techniques can be classified into reversible coding, which is not accompanied by information loss, and irreversible coding, which is so accompanied. Although no information is lost with reversible coding, a certain amount of distortion is usually permitted in speech coding as long as auditory comprehensibility is not impaired. Irreversible coding methods for speech signals can be divided into the waveform coding method and the analysis-synthesis method. Pulse code modulation (PCM) used in the ordinary telephone system is called log PCM because the amplitude is compressed by logarithmic transformation before linear quantization and coding. Adaptive transform coding is a method in which a speech signal is divided into several frequency bands in a way similar to that with subband coding.
