Harmonics-to-noise ratio and psychophysical measurement of the degree of hoarseness.

The degree of hoarseness can be evaluated by judging the extent to which noise replaces the harmonic structure in the spectrogram . The relationship between these two components was quantified as the harmonics-to-noise (H/N) ratio. Eighty-seven phonatory samples (sustained vowel /a/), ranging from nearly normal to severely hoarse, were analyzed. The H/N ratio, the spectrographic classification, and cycle-to-cycle pitch perturbations (jitter) each showed a significant correlation with the psychophysical measurement of the degree of hoarseness (r = .809, .805, and .712, respectively; p less than .001). The analysis also revealed that the correlations of the psychophysical measurement of the degree of hoarseness with the first two parameters were significantly higher than that with jitter (p less than .05). Moreover, the spectrographic classification is subjective, and its scale is discrete and coarse. Therefore, the H/N ratio seems to be the most applicable in the clinic as a quantitative index of the degree of hoarseness.