The method presented herein can be used to display functional vocal fold properties including the absence of oscillation, glottal insufficiency, and phase relations within one single image. The reference data showed that phase asymmetries seem to be frequent even in normophonic speakers.
from the Journal of Voice
The purpose of the study was to investigate relationships between vocal fold vibrations and voice quality. Laryngeal images obtained from high-speed digital imaging (HSDI) were examined for their open-closed timing characteristics and perturbation values. A customized software delineated the glottal edges and used the Hilbert transform-based method of analysis to provide objective quantification of glottal perturbation. Overlay tracings of the transformed glottal cycles provided visual patterns on the overall vibratory dynamics. In this paper, we described the use of this method in looking at vibratory characteristics of a group of young female speakers (N = 23). We found that, females with no voice complaints and who had been perceived to have normal voices were not a homogeneous group in terms of their glottal vibratory patterns during phonation. Their vibratory patterns showed characteristics similar to exemplar voices targeted to be clear (50%), pressed (27%), breathy (15%), or a mixed quality (8%). Perturbation range in terms of cycle-to-cycle frequency and amplitude was small and did not discriminate patterns. All these patterns yielded perceptually normal voices suggesting that in normal young speakers, the level of perturbation may be more important to the judgment than the actual pattern of closure.
from the Journal of Voice
Assessment of the variability of vocal fold dynamics within and between recordings with high-speed imaging and by phonovibrogram
Analysis suggests that endoscopic parameters obtained from phonovibrograms are consistent from day to day in normal voices. Further studies are needed to objectively rate the presence and degree of these parameters in disordered voices. Laryngoscope, 2010
from The Laryngoscope
Decreasing the closing speed of the vocal folds can reduce loudness and energy in the higher frequency harmonics, resulting in reduced voice quality. Our aim was to study the correlation between higher frequencies and the intraglottal vorticity (which contributes to rapid closing by producing transient negative intraglottal pressures).
Using six excised canine larynges (three with symmetric and three with asymmetric, periodic vocal fold motion), intraglottal vorticity was calculated from 2D velocity fields measured using particle imaging velocimetry.
There is a strong correlation between intraglottal vorticity and acoustic energy in the higher frequencies; in periodic asymmetric motion, the vorticity and higher frequencies are both reduced.
For unilateral vocal fold paralysis, these findings suggest one reason why periodic, asymmetric motion, may produce an abnormal voice. Further study will help determine when and why reinnervation, as opposed to medialization, may result in better voice quality. Laryngoscope, 119:216-221, 2009