While a few of these reports included suspect conclusions or demonstrated unfamiliarity with advanced performance practice techniques, a high level of understanding was achieved by the end of the decade.
Clinch et. al. Clinch et al. (1982) performed X-ray fluoroscopic examinations of vocal tract shape changes involved in the playing of the clarinet, soprano saxophone, and recorder. They noted a strong dependence of note quality on vocal tract shape and, somewhat curiously, concluded ``that vocal tract resonant frequencies must match the frequency of the required notes in clarinet and saxophone performance.''
Backus Backus (1985) made vocal tract impedance measurements and found peak values an order of magnitude less than the impedances of the clarinet air column resonances.
Backus also experimented with a clarinet-like system arranged to sound using a vacuum mechanism located at its downstream end. He observed relatively little change in the resulting waveforms when either human or more sharply tuned resonance structures were placed around the vibrating reed/mouthpiece system.
From these results, Backus concluded that ``the player's vocal tract has a negligible influence on the instrument tone.''
where Zu is the input impedance looking upstream from the reed into the player's windway, Zd is the input impedance looking downstream from the reed into the instrument air column, and Zr is the nonlinear acoustic impedance of the reed valve.
The flow through the reed aperture can then be expressed in terms of the pressure difference
and the above equations solved as
The reed impedance plays a secondary role in this expression because it tends to be very large in comparison to the other impedances.
If the upstream impedance (Zu) is negligible, as was assumed for many years, the system can be accurately described in terms of the air column and reed impedances alone. On the other hand, it is clear that if significant impedance peaks occur in the upstream system, they can influence the behavior of the instrument in important ways.
Benade and Hoekje made upstream impedance measurements and found that certain vocal tract configurations can produce strong upstream impedance peaks.
In addition, they noted a number of ways in which upstream resonances could have considerable influence on the entrainment of the reed and the resulting sound spectra.
With respect to the lack of earlier recognition within the acoustics community of the possible influences of a player's windway, Benade Benade (1985) noted that:
every player quickly learns to avoid windway configurations that might adversely affect the instrument response and/or produce undesirable multiphonics;
the audible effects of resonance alignment in the player's windway are rather subtle and not easily recognized in the resulting instrument spectrum;
the ability to make use of vocal tract resonances to strengthen or support instrument oscillations is a refinement that typically comes only with many years of performance experience.
In a later study by Wilson Wilson (1996), upstream resonances were examined during clarinet performance of several musical phenomena.
She found that the performer tends to align upstream resonances with the first or second harmonic of a sounding tone, ``but that there were also a number of tones that did not have an airway resonance aligned with a harmonic.''
For pitchbend, a large-amplitude vocal tract resonance was used to control the playing frequency. When playing multiphonics, Wilson found that the performer creates a resonance that supports an oscillation at a linear combination of the audible pitch frequencies.
Sommerfeldt and Strong Sommerfeldt and Strong (1988) presented a detailed time-domain simulation of a player-clarinet system that included a sixteen segment cylindrical tube approximation for the player's windway.
They explored several vocal tract configurations and found some instances of upstream influence on the resulting sound spectra.