The Perception of Formant Tuning in Soprano Voices

At the upper end of the soprano range, singers adjust their vocal tract to bring one or more of its resonances (R_n) toward a source harmonic, increasing the amplitude of the sound; this process is known as resonance tuning. This study investigated the perception of (R₁) and (R₂) tuning, key strategies observed in classically trained soprano voices, which were expected to be preferred by listeners. Furthermore, different vowels were compared, whereas previous investigations have usually focused on a single vowel.

Listeners compared three synthetic vowel sounds, at four fundamental frequencies (f₀), to which four tuning strategies were applied: (A) no tuning, (B) R₁ tuned to f₀, (C) R₂ tuned to 2f₀, and (D) both R₁ and R₂ tuned. Participants compared preference and naturalness for these strategies and were asked to identify each vowel.

The preference and naturalness results were similar for /ɑ/, with no clear pattern observed for vowel identification. The results for /u/ showed no clear difference for preference, and only slight separation for naturalness, with poor vowel identification. The results for /i/ were striking, with strategies including R₂ tuning both preferred and considered more natural than those without. However, strategies without R₂ tuning were correctly identified more often.

The results indicate that perception of different tuning strategies depends on the vowel and perceptual quality investigated, and the relationship between the formants and (f₀). In some cases, formant tuning was beneficial at lower f₀s than expected, based on previous resonance tuning studies.