Modeling spectral speech transitions using temporal decomposition techniques

ATAL [1] introduced a technique for decomposing speech into phone-length temporal events in terms of overlapping and interacting articulatory gestures. This paper reports on simplifications of this technique with applications to acoustic-phonetic synthesis. Spectral evolution is represented by time-indexed trajectories in the p-dimensional space of Log-Area Ratios{y_{i}= \Ln ((1+k_{i})/(1-k_{i}))}where kiare the reflection coefficients obtained from short-time stationary LPC analysis. The vocal tract configuration (spectral vector) associated with each interpolation function belongs to a finite set of articulatory targets (vector quantization code book). A set of speech segments ("polysons") has been encoded using this technique. It includes diphones, demi-syllables, and other units that are difficult to segment. Temporal decomposition using target spectra can break the complex encoding of these segments. In particular, coarticulation effects are analyticaiy explained and modeled. It is demonstrated that these new tools provide an adequate environment in our search for better rules in acoustic speech synthesis.