Vocal tract configuration and acoustic transfer characteristics in mechanisms of extreme vocal styles-A pilot study

Nonlinear phenomenon common in extreme and traditional singing involves often coupled oscillations of glottal and supraglottic structures. Four such phonatory mechanisms-undertone, distortion, growl, and rattle-differ in supraglottic involvement and frequency ratio between glottal and supraglottic oscillators. However, the contribution of vocal tract (VT) configurations remains insufficiently understood. Using static three-dimensional magnetic resonance imaging and acoustic analysis, we investigated VT shaping in a professional singer. The VT was used to calculate volume-velocity transfer functions and was segmented into seven sub-volumes for geometric analysis. Acoustic recordings provided fundamental frequencies and pitches. Undertone and distortion showed the most speech-like configurations, with ventricular and epilaryngeal volumes largely unaffected by the laryngeal elevation. Growl involved laryngeal lowering and tongue retraction, facilitating epiglottic-arytenoid approximation. Rattle exhibited increased pharyngeal constriction. Growl showed clustering of resonance peaks around 2000-4000 Hz (singer's formant region), and high rattle showed alignment of twice the pitch with the first resonance frequency, suggesting an enhanced source-filter interaction. For this singer, the VT configuration differed systematically across the four phonatory mechanisms. These hypothesis-generating observations underline the potential role of VT configuration of nonlinearities in phonation and motivate larger studies relevant to voice pedagogy and clinical practice involving supraglottic sound production.