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Vocal Tract Influence in Wind Instrument Performance

Participants: Gary Scavone, Antoine Lefebvre, Andrey da Silva, and Vincent Freour

Funding: NSERC Discovery Grant

Period: 2005 - ongoing

Summary

The role and influence of a performer’s vocal tract on the sound of reed-valve wind instruments has been a topic of some debate since the late 1970s. Musicians reported that they could affect the sound of their instruments, sometimes in very significant ways, via vocal-tract manipulations. Acousticians generally agreed that, in order for such influence to exist, the player's upstream windway must exhibit input impedance maxima of similar or greater magnitude to those of the downstream air column. Many acousticians were skeptical this could happen, given the highly damped and compliant nature of the human vocal tract versus the rigid and strongly resonant air column of a wind instrument. At least three scientific Ph.D. theses, seven music Masters or Doctoral theses, and four scientific journal articles focused on the topic but no conclusive evidence was presented to demonstrate, under playing conditions, that the upstream system could override the downstream air column in controlling the reed vibrations.

In (Scavone, 2006), we presented a real-time measurement system that provides a visual comparison of the relative strengths of the “upstream” windway and “downstream” alto saxophone air column impedances under normal playing conditions (without requiring the player to hold or mime a particular oral cavity setting). The system assumes continuity of volume flow on either side of the “reed,” which leads to a direct proportionality between the upstream and downstream pressures and impedances. Playing experiments clearly demonstrated many instances in which vocal-tract manipulations can cause impedance peak magnitudes in the mouth cavity to exceed those in the downstream air column. A more in-depth scientific analysis (Scavone et. al., 2008) subsequently showed that, under certain conditions, saxophone players can create an upstream windway resonance that is strong enough to override the downstream system in controlling reed vibrations. This can occur when the downstream air column provides only weak support of a given note or effect, especially for notes with fundamental frequencies an octave below the air column cutoff frequency and higher. Vocal- tract influence is clearly demonstrated when pitch bending notes high in the traditional range of the alto saxophone and when playing in the saxophone’s extended register. Subtle timbre variations via tongue position changes are possible for most notes in the saxophone’s traditional range and can affect spectral content from at least 800–2000 Hz.

From 2009-2013, efforts were subsequently focused on whether similar influence is possible in brass instruments. Ph.D. student Vincent Fréour used a measurement approach augmented with a novel application of electroglottography to enable the evaluation of phase relationships between the brass player's lip motion and pressure variations in the mouth and mouthpiece. From these results, together with experiments using a mechanical player system and physics-based simulations, we were able to compare different playing strategies used by trombone performers and demonstrate that subtle manipulations of the vocal-tract can be important in optimizing the efficiency and flexibility of their playing in the high range.

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