Date of Award


Degree Name

Master of Arts


Speech, Language and Hearing Sciences

First Advisor

Dr. James M. Hillenbrand

Second Advisor

Dr. Robert L. Erickson

Third Advisor

Dr. John M. Hanley

Fourth Advisor

Dr. Richard Pippen

Access Setting

Masters Thesis-Open Access


This study investigated the perceptual effects of varying glottal waveshape perturbation, duty cycle perturbation, jitter, signal-to-noise ratio perturbation, and shimmer at three levels of perceived magnitude (high, medium, and low). Voice signals were synthesized using a modified version of Klatt's (1980) formant synthesizer. Listeners rated signal dysphonia using an A-B dissimilarity procedure. Multidimensional scaling analysis suggested that signals judged low in magnitude of dysphonia were perceived to be most similar. Medium-level and high-level magnitude signals were judged to be respectively less similar. Signals varying in duty cycle and fundamental frequency perturbation were perceived to be very similar while those signals varying in waveshape and amplitude perturbation were consistently judged to be most different from all other signals within each level of perceived severity. Implications for the development of objective measures vocal quality are discussed.