Determining the Relevant Criteria for Three-dimensional Vocal Tract Characterization.

Objective: Soprano singers face a number of specific challenges when singing vowels at high frequencies, due to the wide spacing of harmonics in the voice source. The varied and complex techniques used to overcome these are still not fully understood. Magnetic resonance imaging (MRI) has become increasingly popular in recent years for singing voice analysis. This study proposes a new protocol using three-dimensional MRI to investigate the articulatory parameters relevant to resonance tuning, a technique whereby singers alter their vocal tract to shift its resonances nearer to a voice source harmonic, increasing the amplitude of the sound produced.

Methods: The protocol was tested with a single soprano opera singer. Drawing on previous MRI studies, articulatory measurements from three-dimensional MRI images were compared to vocal tract resonances measured directly using broadband noise excitation. The suitability of the protocol was assessed using statistical analysis.

Results: No clear linear relationships were apparent between articulatory characteristics and vocal tract resonances. The results were highly vowel dependent, showing different patterns of resonance tuning and interactions between variables. This potentially indicates a complex interaction between the vocal tract and sung vowels in soprano voices, meriting further investigation.

Conclusions: The effective interpretation of MRI data is essential for a deeper understanding of soprano voice production and, in particular, the phenomenon of resonance tuning. This paper presents a new protocol that contributes toward this aim, and the results suggest that a more vowel-specific approach is necessary in the wider investigation of resonance tuning in female voices.