Objective: This study investigated voice source and vocal tract adjustment strategies through measurements of acoustic correlates while reading aloud the "Three Bears Passage", a standard Mandarin reading passage previously developed for eliciting significant vocal range variations, and the effect of voice disorders on vocal flexibility reflected by such adjustments.

Methods: Based on audio recordings of the passage for 30 participants with voice disorders and 30 age- and gender-matched normal controls, fundamental frequency (F0) measures reflecting voice source modulation for the most dramatic sentence in the passage while mimicking the three bear voices versus narrator voice were measured. Formant frequencies (F1-F4), estimated vocal tract length (VTL), and formant dispersion (FD) of the vowel /a/ in the keyword /fan/ of the most dramatic sentence were also measured.

Results: Significant differences in F0, VTL, and FD were found between the mimicked bear voices (Papa bear, Mama bear, Baby bear) and the narrator voice, with distinct patterns of voice source and vocal tract adjustments in individuals with voice disorders.

Conclusions: These findings underscored the intricate interplay between voice source modulation and vocal tract shaping, highlighting how speakers could adjust both the source and the filter to convey role-specific cues and to demonstrate vocal flexibility. Results could advance our understanding of the importance of vocal flexibility control, and how it could be affected by voice disorders.