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Vocal shimmer during the sustained phonation of /a/, /i/, /u/ was investigated for thirty-one adult male speakers using an automatic analysis program. The results showed an overall average shimmer of 0.39 dB with a critical value of 0.98 dB. Significant correlations were found among shimmer, jitter and fo standard deviation.
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Yoshiyuki Horii (1980) studied this question.
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