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Tape recordings before and after successful voice therapy from 174 subjects with non-organic voice disorders (functional dysphonia) were analysed by long-time 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.
Kitzing et al. (Wed,) studied this question.