Estimation of vocal tract shape for VCV syllables for a speech training aid

Display of vocal tract shape can be used in speech training aids for the hearing impaired children, as it provides a visual feedback of the articulatory efforts. Estimation of vocal tract shape, based on LPC and other analysis techniques, works satisfactorily for vowels but generally fails during stop closures. Indication of correct place of articulation is very important, particularly for non-labial consonants. In order to study the dynamics of the vocal tract shape estimation during transitions at vowel-consonant boundaries, we have used "areagram", a spectrogram-like two-dimensional (2D) display of estimated vocal tract cross-sectional area as a function of time and position along the tract length. Area estimation is based on reflection coefficients obtained from LPC analysis of speech. Based on estimated area during the transition segments preceding and following the stop closure, bivariate polynomial surfaces are obtained and these are used for estimation of the vocal tract shape during stop closure by performing 2D interpolation. The place of closure for various stop consonants could be estimated satisfactorily from the conic surface approximation.