A formant-to-area conversion technique based on acoustic sensitivity functions

Abstract

A technique for transforming formant frequencies to vocal tract area functions is developed by using sum and difference combinations of acoustic sensitivity functions to perturb an initial vocal tract configuration. First, sensitivity functions [e.g., Fant and Pauli, Proc. Speech Comm. Sem., Vol. 74 (1975)] are calculated for a neutral area function, at its specific formant frequencies. The sensitivity functions are then multiplied by scaling coefficients that are determined from the difference between a desired set of formant frequencies and those supported by the current area function. Then, the scaled sensitivity functions are summed together to generate a perturbation of the area function. This produces a new area function whose associated formant frequencies are closer to the desired values than the previous one. This process is repeated iteratively until the coefficients are equal to zero or are below a threshold value. Results show that vowel area functions are generated that are comparable to those measured with imaging techniques. The performance of the technique with time-varying formant frequencies will also be discussed. [Work supported by NIH R01-DC04789.]