An Acoustic Examination of Pitch Variation in Soprano Singing

The ability to perform acoustic inspection of data and to correlate the results with perceptual and physiological aspects facilitates vocal behavior analysis. The singing voice has specific characteristics and parameters that are involved during the phonation mechanism, which may be analyzed acoustically.

To describe and analyze the fundamental frequency and formants in pitch variation in the /a/ vowel in sopranos.

The sample consisted of 30 female participants between the ages of 20 to 45 years without vocal complaints. All sustained vowel sounds were recorded with the /a/ vowel sustained for 5 seconds, with three replications at low (C4-261 Hz), medium (Eb4-622 Hz), and high (Bb4-932 Hz) frequencies that were comfortable for the voice classification. In total, 90 samples were analyzed with digital extraction of the fundamental frequency (f0) and the first five formants (F1, F2, F3, F4, and F5) and manual confirmation. The middle segment was considered for analysis, whereas the onset and offset segments were not considered. Subsequently, FFT (fast Fourier transform) plots, LPC (linear predictive coding) graphs, and tube diagrams were created. The Shapiro-Wilks test was applied for adherence and the Friedman test was applied for comparison of paired samples.

For vocalizations at low and medium pitches, higher values were observed for the first five formant frequencies than for the f0 value. Overlaying the LPC and FFT graphs revealed a similarity between F1 and F2 at the two pitches, with clustered harmonics in the F3, F4, and F5 region in the low pitch. At the medium pitch, there was similarity between F3 and F4, an F5 peak, and tuned harmonics. However, in the high-pitch vocalizations, there was an increase in the F2, F3, F4, and F5 values in relation to f0, and there was similarity between them along with synchrony between f0 and F1, H2 and F2, H3 and F3, H4 and F4, and H5 and F5.

Pitch changes indicate differences in the behavior of the fundamental frequency and sound formants in sopranos. The comparison of the sustained vowels sounds in f0 at the three pitches revealed specific vocal tract changes on the LPC curve and FFT harmonics, with an extra gain range at 261 Hz, synchrony between peaks of formants and harmonics at 622 Hz, and equivalence of f0 and F1 at 932 Hz.