Vocal tract acoustic transfer function measurements : further developments and applications

Recent techniques of evaluation of vocal tract acoustic transfer functions are based on the external excitation of the tract at the thyroid cartilage level. This paper presents further developments of methods using Gaussian white noise or pseudo-random sequences. In addition to the traditional non-parametric spectral characterisation, an automatic estimation of formants and bandwidths has been developed using model identification procedures. A user-friendly protocol has been implemented to perform quasi simultaneous recording of transfer functions and radiated sound. This method has been used to study the influence of glottis conditions on formants and bandwidths for the French vowels, and an experimental formant-cavity aflliation index has been defined as the relative bandwidth variation between closed glottis and sound production conditions. Finally a first attempt to characterise the aspiration noise spectrum for whispered vowels has shown that the ovexall source spectral tilt increase with overall SPL.