Study of Closed Phase Resonance Bandwidths for Oral and Nasal Tracts Using Zero Time Windowing

Abstract

The periodic opening and closing of the vibrating vocal folds changes the production system continuously during the production of voiced speech. The subglottal and supraglottal cavities have distinct structure and impedance. A coupling and decoupling of these cavities affects effective length of the vocal tract which in turn affects its impedance. This can be studied based on the shift in the location of dominant resonant frequencies (DRFs) of the instantaneous system response obtained using zero time windowing (ZTW) method. The change in the impedance of the vocal tract is reflected in the bandwidth of spectral resonances. Bandwidth values estimated using the group delay function at dominant resonance locations, approximated by the Hilbert envelope of the numerator of group delay (HNGD) function. An estimate of this change is made by comparing the bandwidths in closed glottal phase of the glottal cycle for the oral and nasal tracts. A study of the relative difference in the bandwidth of vowels and nasals in speech is attempted to compare the impedance of the respective tracts. The study examines VC/CV segments in English for speakers in the TIMIT database. The results show that the nasal segments exhibit higher bandwidth values compared to vowels.