Speech and vocoders

Speech signals are produced by relatively slow articulatory movements. This suggests that the information rate of the speech signal is much less than would be expected by considering the bandwidth of the acoustic signal. Vocoders attempt to exploit the redundancy in the speech waveform by extracting and transmitting the information bearing parameters of the speech signal. At the receiver, these parameters are used to control a speech synthesizer that reproduces the original signal without any serious loss of intelligibility but with some degradation of quality. The paper describes speech production principles, and their application to speech synthesis; the operation of various types of vocoder and the problems of pitch extraction.