Vocal-Tract Influence during Saxophone Performance

Gary P. Scavone, Antoine Lefebvre, and Andrey R. da Silva

Music Technology, Schulich School of Music

Introduction

Research in the Computational Acoustic Modeling Laboratory (CAML) with regard to measuring vocal-tract influence in saxophone performance has been ongoing since 2005.

A complete description of this work and the results are reported in:

Scavone, G., Lefebvre, A., and da Silva, A. (2008) "Measurement of vocal-tract influence during saxophone performance." Journal of the Acoustical Society of America, 123, pp. 2391-2400.

ABSTRACT: This paper presents experimental results that quantify the range of influence of vocal tract manipulations used in saxophone performance. The experiments utilized a measurement system that provides a relative comparison of the upstream windway and downstream air column impedances under normal playing conditions, allowing researchers and players to investigate the effect of vocal-tract manipulations in real time. Playing experiments explored vocal-tract influence over the full range of the saxophone, as well as when performing special effects such as pitch bending, multiphonics, and ``bugling''. The results show that, under certain conditions, 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.

Previous results were reported in 2006:

Scavone, G. "Real-time measurement/viewing of vocal-tract influence during wind instrument performance," Journal of the Acoustical Society of America, 119:3382(A), June 2006.

ABSTRACT: Since the early 1980s, there have been a number of investigations into the role and influence of a player's vocal tract on the sound production of wind instruments. While the underlying acoustic principles are relatively well understood, a general lack of agreement remains within both the music acoustics and performance communities with regard to the importance of this mechanism during playing conditions. Disparities arise in part because subtle manipulations of the oral cavity can affect the response of the instrument without necessarily producing effects audible to an observer. A real-time measurement system is demonstrated that provides a visual comparison of the relative strengths of the "upstream" windway and "downstream" air column impedances under playing conditions. 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 demonstrate many instances in which vocal-tract manipulations can cause impedance peak magnitudes in the mouth cavity to exceed those in the downstream air column. In addition to providing visual "proof" of such manipulations, the system is expected to offer a pedagogical tool to help performers better learn how to make use of this control mechanism.

This site is intended to provide further details on the measurement system.

Mouthpiece Setup

A stock alto saxophone mouthpiece, sold by Twigg Musique in Montreal, Canada, was fitted with two Endevco pressure transducers to measure the sound pressure inside the mouthpiece as well as inside the player's mouth. A groove was carved into the top of the mouthpiece to allow the 8507C-1 transducer to be positioned 3 mm behind the front edge of the mouthpiece tip. The 8510B-1 pressure transducer was threaded through the top of the mouthpiece about 5.5 centimeters from the mouthpiece tip to obtain internal pressure values.

Figures 1 and 2: The mouthpiece groove and the Endevco transducers (click to enlarge).

Figures 3 - 5: The complete mouthpiece system (click to enlarge).

Measurement System

The Endevco pressure transducers were connected to an Endevco 136 differential voltage amplifier and the signals from there were connected to a National Instruments (NI) PCI-4472 8-channel dynamic signal acquisition board (only four channels were used in this study). A small force sensing resistor (8 mm diameter) made by Interlink Electronics was placed under the cushion on the top of the saxophone mouthpiece to measure relative lip pressure. When the experiment was conducted, the external sound was recorded using a Sennheiser KE4-211-2 pressure capsule amplified by a Unides Design conditioning unit.

Figures 6 and 7: The mouthpiece and saxophone system with player (click to enlarge).

Figures 8 and 9: The mouthpiece and saxophone system in the IAC double-walled sound isolation booth (click to enlarge).

LabVIEW Interface

An NI LabVIEW virtual instrument was designed to allow realtime display of the spectra of the two pressure signals from the mouthpiece, as well as the lip and external pressures. When the "record" button is depressed in the interface (shown below), all four channels of data are also saved to a binary file in 8-byte floating-point format for subsequent analysis in Matlab.

Figure 10: The LabVIEW interface (click to enlarge).

Demonstration Video

The following video shows the measurements system and examples of its use while playing in the tradition and extended register of the alto saxophone, as well as special effects such as pitchbend, bugling, and multiphonics. The waveform in red is the internal mouthpiece pressure spectrum, while the waveform in white is the pressure spectrum inside the player's mouth.

Video