Low bit rate speech coding by concatenation of sound units and prosody coding

The purpose of this work was to develop a speech coding system working at a very low bit rate (100 bits/s) and capable of reproducing natural sounding speech. The approach chosen was to use a concatenation of small sound segments to assemble a sentence along with duration and pitch contour extracted (by Dynamic Time Warping) from a natural utterance of the same sentence. The segmental aspect is coded at the phonological level, thus leading to a bit rate around 60 bits/s. The decoding of the phonemes is obtained by a set of rules operating on phonetic features. The prosodic aspect is coded using stored pitch contours and duration patterns, thus leading to a bit rate around 40 b/s.