The vocal quality of a patient is modeled by means of a Dysphonia Severity Index (DSI), which is designed to establish an objective and quantitative correlate of the perceived vocal quality. The DSI is based on the weighted combination of the following selected set of voice measurements: highest frequency (F(0)-High in Hz), lowest intensity (I-Low in dB), maximum phonation time (MPT in s), and jitter (%). The DSI is derived from a multivariate analysis of 387 subjects with the goal of describing, purely based on objective measures, the perceived voice quality. It is constructed as DSI = 0.13 x MPT + 0.0053 x F(0)-High - 0.26 x I-Low - 1.18 x Jitter (%) + 12.4. The DSI for perceptually normal voices equals +5 and for severely dysphonic voices -5. The more negative the patient's index, the worse is his or her vocal quality. As such, the DSI is especially useful to evaluate therapeutic evolution of dysphonic patients. Additionally, there is a high correlation between the DSI and the Voice Handicap Index score.

Although the perceptual GRBAS scale for pathological voice quality has been found to be sufficiently reliable in clinical practice, even experienced raters disagree to some extent, and the degree of disagreement depends on the perceptual characteristics. We looked for a possible link between the degree of disagreement (65 voices; 2 experienced raters) and objective acoustical measurements. No significant correlation appeared between any acoustical parameter and the degree of disagreement for G. By contrast, the difference in perceptual rating of R was related to the amount of shimmer, and the difference in perceptual rating of B was related to some extent to the amount of jitter. Thus the presence of a strong breathy component in a pathological voice disturbs the rating of the rough component, and reciprocally.

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We have applied high-resolution vocal frequential analysis to a population of singing voices. Two important elements have become apparent: (1) Confirmation that the singing formant originates in the resonators. This is observed especially on a low fundamental, and it is acquired through technical skill and experience. (2) Observation of the vibrato, which, isolated from the clinical study, regarding only its graphic presentation, could have been interpreted as Ê»abnormal’.