Amplitude Effects of Vocal Tract Resonance Adjustments When Singing Louder

In the literature on vocal pedagogy we may find suggestions to increase the mouth opening when singing louder. It is known that sopranos tend to sing loud high notes with a wider mouth opening which raises the frequency of the first resonance of the vocal tract (f_R1) to tune it close to the fundamental. Our experiment with classically trained male singers revealed that they also tended to raise the f_R1 with the dynamics at pitches where the formant tuning does not seem relevant. The analysis by synthesis showed that such behaviour may contribute to the strengthening of the singer's formant by several dB-s and to a rise in the centre of spectral gravity. The contribution of the f_R1 raising to the overall sound level was less consistent. Changing the extent of the mouth opening with the dynamics may create several simultaneous semantic cues that signal how prominent the produced sound is and how great the physical effort by the singer is. The diminishing of the mouth opening when singing piano may also have an importance as it helps singers to produce a quieter sound by increasing the distance between the f_R1 and higher resonances, which lowers the transfer function of the vocal tract at the relevant spectral regions.