DERIVING VOCAL-TRACT AREA FUNCTIONS FROM MIDSAGITTAL PROFILES AND FORMANT FREQUENCIES - A NEW MODEL FOR VOWELS AND FRICATIVE CONSONANTS BASED ON EXPERIMENTAL-DATA
In order to achieve better understanding of the articulatory-acoustic relationships, more data are still very much needed. The two-fold aim of the present study was thus (1) to provide a set of coherent midsagittal functions, area functions and formant frequencies, for a small corpus of vowels and fricative consonants produced by one subject, and (2) to derive a midsagittal profile to area function conversion model optimised for this given subject. Simultaneous tomography and sound recording were available for the subject, as well as some complementary data such as lip geometry or casts of the hard palate. The model is based on Heinz and Stevens' A = alpha d(beta) area function model, modified so that alpha varies continuously along the vocal tract midline as a function of the midsagittal distance. The coefficients of the model have been determined with the help of an optimisation algorithm based on a gradient descent technique. The gradient of the error between actual and desired formant values was computed through a back-propagation network implementing both sagittal-to-area conversion and acoustic wave propagation. The fact that the model should work for sounds as different as vowels and consonants and be coherent at both midsagittal and acoustic levels ensures the reliability of the area functions determined in such a way.
area function midsagittal profile articulatory acoustic relationship articulatory data