Vocal tract contribution to vocal intensity: Interaction between vocal fold adduction, formant tuning, and fundamental frequency

The goal of this study was to understand the interaction between the voice source spectral shape, formant tuning, and fundamental frequency in determining the vocal tract contribution to vocal intensity. Computational voice simulations were performed with parametric variations in both vocal fold and vocal tract configurations. The vocal tract contribution to vocal intensity was quantified as the difference in the A-weighted sound pressure level between the radiated sound pressure and the sound pressure at the glottis. The results from the simulations showed that the vocal tract contribution to vocal intensity depends strongly on the amplitude of the first vocal tract resonance. Two strategies to increase vocal tract contribution to vocal intensity were identified. The first strategy was to increase vocal fold adduction, which increases the relative prominence of the harmonics near the first vocal tract resonance. The second strategy was to bring a vocal tract resonance and a nearby harmonic closer in frequency, often known as formant tuning. In this study, increasing vocal fold adduction was the primary strategy at low fundamental frequencies, whereas formant tuning was more effective at high fundamental frequencies, particularly when formant tuning involves the strongest harmonic in the voice source spectrum.