New approach to very low-rate speech coding using temporal decomposition

Temporal decomposition (TD) is a method to reduce the correlation between speech spectral parameter sets using orthogonalization. The resulting parameters (so-called weightings or target vectors) correspond, mostly, to least-dependent phonetic states, which produce the desired sounds. Other phonetic states can be interpreted as transition states which force the event functions to overlap. On the basis of this assumption, we propose to approximate the event functions by simple functions to focus on the phonetically important states, and to use the resulting parameters for constructing a very low-rate speech coder. The objective and subjective evaluation of synthesized speech, mostly from the intelligibility view point, confirm the assumptions made on the events.