Segmental prototype interpolation coding

Current parametric speech coding schemes can achieve high communications quality speech at bit rates in the range of 2.4 to 1.5 kbits/sec. Most schemes sample and quantise, at regular intervals, the “tracks in time” generated by the parameters of the speech production model. As a result, reconstructed “parameter tracks” do not evolve “smoothly” with time. Furthermore, no advantage is taken of the “linguistic event” nature of speech. In this paper, model parameter “time tracks” are split into non-overlapping speech “event” related segments. These segment based evolutions of model parameters are then vector quantised to provide at the receiver a smooth and subjectively meaningful reconstruction. Thus the paper presents an application of this generic segmental speech model quantisation approach to a 1.5 kbits/sec prototype interpolation coding (PIC) system. Results indicate that the proposed methodology can almost halve the bit rate of this PIC system while preserving overall recovered speech quality