OBJECTIVES: Objective measurements in general and acoustic measurements in particular have become a substantial aspect of voice assessment during the last few decades and studies have established that normative data is necessary for acoustic analysis. Voice acoustic analysis including fundamental frequency (F(0)), jitter, shimmer, harmonics-to-noise ratio (HNR), and maximum phonation time (MPT) can now be easily recorded and analyzed using a computer. Because these systems are widely used in clinical practice, this study was designed to establish the normal acoustic analysis parameters in normal Iranian adults. METHODS: A group of 90 unpaid, healthy, randomly selected subjects with normal voices (45 Iranian men and 45 Iranian women), was selected for this study. Data collection was carried out, using the Dr. Speech Software (subprogram: vocal assessment version 4.0 from Tiger Electronics) at the speech therapy clinic under comfortable phonation. Each gender was separated equally into three age subgroups. Then differences between gender and age subgroups were investigated by statistics software SPSS 13.0. RESULTS: The value of (vowels /a/ and /i/) was greater for females (214.64+/-1.16; 228.06+/-1.5 Hz) than for males (112.82+/-0.94; 126.13+/-1.49 Hz). Conversely, the value of MPT was greater for males (26.30+/-1.29 s) than for females (18.56+/-0.88 s). There were no significant differences in average shimmer and jitter between females (1.21+/-0.03%; 0.22+/-0.01%) and males (1.22+/-0.02%; 0.23+/-0.02%). However, the value of HNR was greater for females (18.81+/-0.96 dB) than for males (18.42+/-0.57 dB). CONCLUSIONS: The present study developed a body of normal data for various parameters of acoustic analysis in different age groups and genders of normal Iranian adults. It seems that the majority of voice characteristics of adults was relatively stable and did not change with aging between 20 and 50 years. However, the voice characteristics of adults older than 50 years were not recorded in this study and therefore require further investigation.
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