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The effects of prolonged (5 × 45 min) reading (loading) on time-based glottal waveform parameters of normal female and male subjects (n = 80) were studied. Two rest (morning and noon) and three loading (two in the morning and one in the afternoon) samples were recorded and analyzed. The glottal waveforms were obtained by inverse filtering of the acoustical signal using an automatic method. The following time-based parameters were analyzed from the estimated glottal flow waveform: (1) length of fundamental period (T); (2) open quotient (OQ); (3) speed quotient (SQ); (4) closing quotient (C1Q). The analysis was based on inverse filtering of the first stressed syllable of ‘paappa’ words produced with normal, maximally soft and maximally loud phonation. In the morning samples the loading affected only the T and OQ values of normal phonation in a statistically significant manner. In the afternoon all the quotient values changed statistically significantly in loud and normal phonation. On the basis of increased SQ and decreased C1Q values of females it is hypothesized that the female voices tended to change towards hyperfunction due to vocal loading.

The effects of prolonged (5 × 45 min) reading in different environmental and ergonomic conditions on time-based glottal waveform parameters of normal female and male subjects (n = 80) were studied. The exposure groups (n = 5 females and males per cell) consisted of eight combinations of the following factors: (1) normal ( < 65 dB) or high ( > 65 dB) speech output level; (2) sitting or standing posture; (3) low (25 ± 5%) or high (65 ± 5%) relative humidity of ambient air. Two rest (morning and noon) and three loading (two in the morning and one in the afternoon) samples were recorded and analyzed. The glottal waveforms were obtained by inverse filtering of the acoustical signal using an automatic method. The following time-based parameters were analyzed from the estimated glottal now waveform: (1) length of fundamental period; (2) open quotient; (3) speed quotient, and (4) closing quotient. The analysis was based on inverse filtering of the first stressed syllable of ‘paappa’ words repeated 3x5 times with normal, maximally soft and maximally loud phonation. Humidity was a significant factor in serveral instances. The interactions between gender and the loading factors were striking.

It is a common experience that vocal quality changes during a break in vocal loading. The purpose of the present study was (1) to analyse the effects of a short post-loading vocal rest in terms of changes in a large variety of voice parameters and (2) to assess the possible effects of gender and exposure factors on these changes. The voices of a randomly chosen group of 40 female and 40 male young students were loaded by having them read aloud a novel. Two sets of voice samples were recorded: a post-loading sample after three times 45-min vocal loading during the morning and a post-resting sample after a 45-min lunch break. The material recorded consisted of /pa:ppa/ words produced normally, as softly and as loudly as possible in this order. The long /a/ vowel of the test word was inverse-filtered to obtain the glottal flow waveform. Time-domain parameters of the glottal flow [open quotient, closing quotient (ClQ), speed quotient (SQ), fundamental frequency (F₀)], amplitude-domain parameters of the glottal flow [glottal flow, minimum of the first derivative of glottal flow, amplitude quotient (AQ)], intraoral pressure and sound pressure level (SPL) values of the phonations were analysed. Voice range profiles and the singer’s formant (g/G, a/A, c^∣/c, e^∣/e, g^∣/g for females/males) of the loud phonations were also measured. The subjects were divided into eight exposure groups (5 females and 5 males per cell) according to different combinations of the following exposure factors: (1) low (25 ± 5%) or high (65 ± 5%) relative humidity of ambient air, (2) low [<65 dB(A)] or high [>65 dB(A)] speech output level during vocal loading and (3) sitting or standing posture during vocal loading. Statistically significant differences between the post-loading and post-resting samples could be observed in many parameters (the values of intraoral pressure in the soft phonations decreased, the values of SPL and SQ in the normal phonations decreased and the values of AQ, F₀ and ClQ in the normal phonations increased). Most of the differences reflected a shift towards softer phonation. Gender and exposure factors also had significant effects.