Tape recordings before and after successful voice therapy from 174 subjects with non-organic voice disorders (functional dysphonia) were analysed by longtime averaged voice spectrograms (LTAS). In female as well as in male voices there was a statistically significant increase in level in the first formant region of the spectra. In the female voices there was also an increase in level in the region of the fundamental. The LTAS were compared to the results of a perceptual evaluation of the voice qualities by a small group of expert listeners. There was no significant change of the LTAS in voices with negligible amelioration after therapy. In the voices, where the change after therapy was perceptually rated to be considerable, the LTAS showed only an increase in intensity, but the general configuration of the spectral envelope remained unchanged. There was only a weakly positive correlation between the quality ratings and parameters of the spectra.

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Various sources of phonetogram variation were investigated, i.e. graphs showing voice sound pressure level (SPL) for a speaker’s loudest and softest phonation at different fundamental frequencies. The short-term SPL variation within a vocalization was analyzed for 10 female and 10 male normal speakers and for 10 female patients with nonorganic dysphonia, i.e. patients with insufficient voices and no indication of pathology according to microlaryngostroboscopy. This variability was about 5 dB in soft phonation and less in loud phonation. The agreement between 2 investigators independently determining SPL for identical vocalizations by means of a sound-level meter was also studied and found to be quite good. The long-term variation was analyzed in 1 male and 1 female normal subject in 15 phonetogram recordings made on different days; the standard deviation averaged across fundamental frequency and subjects was found to be approximately 3 dB. The implications of these findings for a clinical use of phonetograms are discussed.

The clinical usefulness of the phonetogram, i.e. a graph showing the sound pressure level (SPL) of softest and loudest possible phonation over the entire fundamental frequency range of a voice, was investigated. Phonetograms of 29 female non-organic dysphonic patients, 17 healthy female subjects, 18 non-organic dysphonic male patients and 12 healthy male subjects were compared. The female patients showed significantly lower SPL values for loudest phonation when compared with healthy female subjects, while no significant difference was seen in the male subjects in this regard. With respect to the SPL values for softest phonation, on the other hand, the male dysphonic patients showed significantly higher SPL values than the healthy male subjects, whereas no significant difference was seen in the female subjects. Spectrum analysis showed that the patients had a more dominating fundamental in loud phonation than did the healthy voices.