Transfer functions of solid vocal-tract models constructed from ATR MRI database of Japanese vowel production

The ATR MRI database of Japanese vowel production was used to evaluate the acoustic characteristics of the vocal tract for the five Japanese vowels through the measurements of frequency responses from solid vocal-tract models formed by a stereolithographic technique. The database includes speech sounds as well as volumetric magnetic resonance imaging (MRI) data, but the speech sounds were recorded separately from the acquisition MRI data; therefore, their speech spectra are not appropriate for use as the reference for the transfer functions of the vocal tract. A time-stretched pulse signal generated from a horn driver unit was introduced into the physical model at the lips, and the response signals of the models were recorded at the model's glottis. In the measurements, the glottis of the models was sealed with a plastic plate, and the response signals were measured from a small hole in the plate using a probe microphone. This method permits accurate measurement of the transfer functions of the vocal tract under a closed-glottis condition. The resulting transfer functions of the five Japanese vowels provide a benchmark for testing numerical analysis methods that have been used to study vocal-tract acoustics, although the solid wall decreases the frequencies of lower resonances.