Measurements of vocal tract shapes using magnetic resonance imaging

Magnetic resonance imaging is used to determine the vocal tract area functions of a speaker producing five steady vowel sounds. The data is used in an acoustic tube model, formed by concatenating short uniform sections, and the acoustic spectra of the computed output from the model are compared with those of natural speech. For all but one of the vowels good agreement (typically within 120 Hz) is obtained for the first three formant frequencies. To compensate for measurement errors, optimisation procedures are applied, aimed at adjusting the areas to minimise a chosen cost function. A cost function which combines a windowed cepstral error with a Euclidean distance penalty for the areas is effective in finding area functions that gave much closer spectral matches, but which still lie largely within the estimated errors of measurement. These adjusted functions provide suitable root shapes for use in articulatory speech synthesis.