Akustičke značajke vokalnoga zamora
Acoustic characteristics of vocal fatigue

Summary/Abstract: Vocal fatigue is characterized by self-perceived increased laryngeal strain and voice quality changes. The condition can have organic or/and functional causes. Typically, it affects vocal professionals, and teachers are most numerous among them. Despite great number of studies, many questions about vocal fatigue such as its acoustic characterstics are still open. The hypothesis of the present study conducted on female teachers was that there are significant differences in acoustic variables between vocally fatigued teachers (N=23) and teachers without it (N=27). Running speech and prolonged phonation of the vowel /a/ were analyzed in PRAAT software calculating the long-term average speech spectrum LTASS and harmonic spectrum. The average speech F0 and series of spectral variables were calculated: the strength of the strongest spectral peak L0, the α ratio of the level difference above and bellow 1 kHz for the 0-5 kHz range analyzed, and the variables Δ1, Δ2, Δ3 and Δ4 showing the ratios of the respective spectral energy bands of 1-2 kHz, 2-3 kHz, 3-4 kHz and 4-5 kHz relative to the 0-1 kHz reference. The average H1/H2 ratio based on harmonic spectrum of three samples of the prolonged vowel /a/ production was calculated as well. The hypothesis was tested by multivariate and univariate analyzes of variance and discriminant analysis. The results showed that there are no significant differences in the set of acoustic variables between the two teacher groups, thus the hypothesis was rejected. However, the average speech F0 showed to be strong single discriminator. Its mean value in the group of teachers with vocal fatigue, that is 176 Hz, suggests dysfunction. Several factors may explain the absence of acoustic differences between the two groups, one of the most compelling of which is the fact that both groups reported similar numbers of subjective vocal and physical complaints. The results confirm the complex phenomenology of vocal fatigue syndrome, and suggest that acoustic analysis may have limited power to detect it.

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