The interplay between vowels, pitch targets, and voice quality in singing

One strategy in singing is to change the resonance space depending on the target pitch to bridge register shifts. However, the systematic relationship between resonance space adjustments and timbre remains understudied. We investigate whether pitch-dependent vowel modification contributes to voice quality changes. Twenty-three lay speakers participated in an articulatory experiment with ultrasound tongue imaging and electroglottography (EGG). Participants were asked to sing five sets of English vowels across their pitch range in ascending semitone steps. Midsagittal tongue images were splined with DeepLabCut, and closed quotients (CQ) were extracted from the EGG signals. Functional principal component analysis was applied to the tongue splines to evaluate their relationship with CQ. Preliminary results show a nonlinear relationship between voice quality and pitch height, with more modal voice quality in a large portion of the lower end of the pitch range, gradually moving toward a breathier voice quality before becoming tenser again at higher pitches. Tongue position adjustments also contributed to the gradual change in voice quality as the pitch increases; an effect most apparent for participants with a vocal range larger than one octave. Findings highlight the complex interplay between tongue position, voice quality, and pitch targets, showcasing the coordination between source and filter structures.