Changes in voice during a day in normal voices without vocal loading.

Various changes in vocal parameters have been observed during the working days of voice professionals, e.g. teachers. The present study investigated vocal parameters during daytime when voice was not used. Eleven females and ten males (mean ages 30 and 40 years) volunteered as subjects. They recorded the same reading task in the forenoon and in the afternoon with an interval of 6-8 hours. Between the recordings voice use was avoided. Six females repeated the test in six days with the intervals from one week to three months. Fundamental frequency (F0) and sound pressure level (SPL) were measured. Voice quality was studied by calculating the alpha ratio (SPL 1000-5000 Hz/SPL 50-1000 Hz). In most cases F0 was higher in the afternoon, although the change was on the average small (in most cases within 5 Hz) and statistically non-significant. Alpha ratio was significantly higher for the females and lower for the males in the afternoon. Similar changes have been reported after vocal loading. The results suggest that studies on the effects of vocal loading should also address changes in vocal parameters when no vocal loading is present. Gender difference in the vocal changes warrants further study.