Very low rate speech coding using temporal decomposition

A method for encoding the spectral characteristics of speech, at rates below 180 bit/s, using hierarchical temporal decomposition (HTD) is proposed. A set of the log-area-ratio (LAR) parameters, extracted from a given block of speech, are approximated through Gaussian interpolation between the most-steady frames detected by the HTD. This results in a smaller set of parameters which are encoded using vector quantisation. It is shown that the same spectral distortion is obtained with the new coder at a rate of 180 bit/s as that using a scalar quantisation, TD-based coder, at 600 bit/s