The quantitative evaluation of hoarseness.

As the degree of judged hoarseness increases, the noise component appears to a greater degree and replaces the harmonic structure in the spectrogram. The relationship between these two components has been quantified as the harmonics to noise (H/N) ratio. The computation is straightforward; 50 consecutive pitch periods of a sustained vowel /a/ are averaged; H is the energy of the average waveform, while N is the mean energy of the differences between the individual periods and the average waveform. Therefore, the H/N ratio could be measured in the clinic with the aid of a small, inexpensive computer. This H/N ratio was successfully applied for evaluating the effectiveness of the treatments for hoarseness. Although the H/N ratio does not aid in making a diagnosis of laryngeal abnormality, it would be an important tool for assessing hoarseness.