Impact of human vocal fold vibratory asymmetries on acoustic characteristics of sustained vowel phonation

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 127-132).Clinical voice specialists make critical diagnostic, medical, therapeutic, and surgical decisions by coupling visual observations of vocal fold tissue motion with auditory-perceptual assessments of voice quality. The details of the relationship between vocal fold tissue motion and the voice produced are not fully understood, and there is recent evidence that the diagnostic significance of asymmetries during vocal fold vibration may be over-interpreted during clinical voice assessment. An automated system based on high-speed videoendoscopy recordings was developed to objectively quantify vocal fold vibratory asymmetry with initial validation from manual markings and visualperceptual judgments. Efficient estimation of these measures was possible due to recent technological advances in high-speed imaging of the larynx that enabled the capture and processing of high-resolution video (up to 10,000 images per second) of rapid vocal fold vibrations (100-1000 times per second). Synchronized recordings of the acoustic voice signal were made to explore physiological-acoustic relationships that were not possible using clinical stroboscopic imaging systems. In an initial study of asymmetric vibration in 14 patients treated for laryngeal cancer, perturbations in the voice signal were most associated with asymmetry that changed across vibratory cycles, while the overall level of asymmetry did not contribute to degradations in voice quality measures.(cont.) Thus, since stroboscopic imaging is only able to capture vibratory asymmetry that occurs periodically, voice clinicians are not able to observe the time-varying nature of asymmetry that presumably affects acoustic perturbations to a higher degree. The impact of asymmetric vibration on spectral characteristics was explored in a computational voice production model and an expanded group of 47 human subjects. Surprisingly, in both model and subject data, measures of vocal fold vibratory asymmetry did not correlate with spectral tilt measures. In the subject data, left-right phase asymmetry and closing quotient exhibited a mild inverse correlation. This result conflicted with model simulations in which the glottal area waveform exhibited higher closing quotients (less abrupt glottal closure) with increasing levels of phase asymmetry. Results call for further studies into the applicability of traditional spectral tilt measures and the role of asymmetric vocal fold vibration in efficient voice production.by Daryush Dinyar Mehta.Ph.D

Aspiration noise during phonation : synthesis, analysis, and pitch-scale modification

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 139-145).The current study investigates the synthesis and analysis of aspiration noise in synthesized and spoken vowels. Based on the linear source-filter model of speech production, we implement a vowel synthesizer in which the aspiration noise source is temporally modulated by the periodic source waveform. Modulations in the noise source waveform and their synchrony with the periodic source are shown to be salient for natural-sounding vowel synthesis. After developing the synthesis framework, we research past approaches to separate the two additive components of the model. A challenge for analysis based on this model is the accurate estimation of the aspiration noise component that contains energy across the frequency spectrum and temporal characteristics due to modulations in the noise source. Spectral harmonic/noise component analysis of spoken vowels shows evidence of noise modulations with peaks in the estimated noise source component synchronous with both the open phase of the periodic source and with time instants of glottal closure. Inspired by this observation of natural modulations in the aspiration noise source, we develop an alternate approach to the speech signal processing aim of accurate pitch-scale modification. The proposed strategy takes a dual processing approach, in which the periodic and noise components of the speech signal are separately analyzed, modified, and re-synthesized. The periodic component is modified using our implementation of time-domain pitch-synchronous overlap-add, and the noise component is handled by modifying characteristics of its source waveform.(cont.) Since we have modeled an inherent coupling between the original periodic and aspiration noise sources, the modification algorithm is designed to preserve the synchrony between temporal modulations of the two sources. The reconstructed modified signal is perceived to be natural-sounding and generally reduces artifacts that are typically heard in current modification techniques.by Daryush Mehta.S.M