Analysis by synthesis of pathological voices using the Klatt synthesizer

Abstract The ability to synthesize pathological voices may provide a tool for the development of a standard protocol for assessment of vocal quality. An analysis-by-synthesis approach using the Klatt formant synthesizer was applied to study 24 tokens of the vowel /a/ spoken by males and females with moderate-to-severe voice disorders. Both temporal and spectral features of the natural waveforms were analyzed and the results were used to guide synthesis. Perceptual evaluation indicated that about half the synthetic voices matched the natural waveforms they modeled in quality. The stimuli that received poor ratings reflected failures to model very unsteady or “gargled” voices or failures in synthesizing perfect copies of the natural spectra. Several modifications to the Klatt synthesizer may improve synthesis of pathological voices. These modifications include providing jitter and shimmer parameters; updating synthesis parameters as a function of period, rather than absolute time; modeling diplophonia with independent parameters for fundamental frequency and amplitude variations; providing a parameter to increase low-frequency energy; and adding more pole-zero pairs.