Effect of Vocal Tract Resonances on the Sound Spectrum of the Saxophone

Abstract

Variation in the radiated sound spectrum, prad, is an expressive technique that can be achieved on the saxophone by employing different vocal tract configurations that change the vocal tract impedance spectrum Zmouth. However, the relation between prad and the vocal tract impedance spectrum Zmouth has not previously been measured for orchestral instruments. In this study, prad and Zmouth were measured simultaneously over the frequency range from 100 to 10000 Hz while saxophonists played. For notes sounded over the normal and altissimo playing range, experienced saxophonists are able to produce distinctive variations in the spectral envelope of the radiated sound, without changing the pitch or the amplitude of the fundamental, using different vocal tract configurations. When Zmouth was adjusted to have magnitudes comparable with the input impedance of the bore, Zbore, harmonics of prad were usually increased at nearby frequencies, both for the range over which the saxophone has strong resonances (1002000 Hz) and for the higher range (2-10 kHz). Less experienced players who are unable to produce strong peaks in Zmouth produce much smaller variations in prad. prad correlates more strongly with the series impedance Zmouth + Zbore: for large values of |Zmouth|, larger series impedance at a particular frequency always produced larger radiated power. The change in sound inside the mouth is proportionally larger than that in prad, which explains why players judge the timbre to be more changed than do listeners.