Segmental quantization of speech spectral information

The majority of current speech coding algorithms for medium-to-low bit rates transmit two information components, a short-time spectrum estimate and an excitation signal. Even though advanced intraframe quantization schemes have been proposed, the spectral information still consumes large proportion of the available bit rate. For many speech sounds, the speech spectrum is relatively smooth for time intervals much longer than the sampling rate of the spectrum estimates. Thus, compression can be obtained by identifying smoothly varying segments of the speech spectrum and only transmitting the spectral information once for each segment. The segment spectral information is then an approximation to the true spectrum, but if the segmentation criterion is properly chosen, the induced distortion can be controlled to be within the acceptable 1 dB mean spectral distortion limit. In the present paper the author shows that segment quantization can be applied to reduce the required bit rate for the spectral information by a factor of approximately two without compromising the total spectral distortion