Pitch Synchronous Analysis of Voiced Sounds

A study of vowel sounds by means of a spectral analysis keyed synchronously to the voice pitch has been carried out. Spectra are obtained by Fourier analysis of individual pitch periods which were established by visual inspection of oscillogram. A digital computer served as the analyzer. The spectra are represented by a pattern of zeros and poles obtained by a process of successive approximation, again carried out by computer. The contributions from vocal tract and glottal source can be uniquely separated and examined. These results show that vowel sounds can be represented by a sequence of poles arising from the vocal tract and a sequence of zeros character the izglottal excitation. The frequencies of the vocal tract poles agreed with previous measurements, but the damping factors were not entirely consistent with earlier estimates. The zeros showed approximately uniform frequency spacing, particularly at high frequencies. A theoretical development indicated that this characteristic was to be expected from the known structure of the glottal excitation. The zero pattern was used to estimate the ratio of open-to-closed time for the glottis during voicing.