Effect of artificially lengthened vocal tract on vocal fold oscillation's fundamental frequency

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Date: June 2004
From: Journal of Voice(Vol. 18, Issue 2)
Publisher: Elsevier, Inc.
Document Type: Article
Length: 2,291 words

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Summary: The fundamental frequency of vocal fold oscillation ([F.sub.0]) is controlled by laryngeal mechanics and aerodynamic properties. [F.sub.0] change per unit change of transglottal pressure (dF/dP) using a shutter valve has been studied and found to have nonlinear, V-shaped relationship with [F.sub.0]. On the other hand, the vocal tract is also known to affect vocal fold oscillation. This study examined the effect of artificially lengthened vocal tract length on dF/dP. dF/dP was measured in six men using two mouthpieces of different lengths. Results: The dF/dP graph for the longer vocal tract was shifted leftward relative to the shorter one. Conclusion: Using the one-mass model, the nadir of the "V" on the dF/dP graph was strongly influenced by the resonance around the first formant frequency. However, a more precise model is needed to account for the effects of viscosity and turbulence.

Key Words: Fundamental frequency--Transglottal pressure--Vocal tract--First formant frequency--One mass model.

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INTRODUCTION

The fundamental frequency of vocal fold oscillation ([F.sub.0]) is responsible for the pitch of voiced sound and plays a great role in singing and speaking. [F.sub.0] is thought to be a function of the vocal fold's length, stiffness, and subglottal pressure. The first and second factors are regulated by the intrinsic laryngeal muscles, and the third is regulated by the respiratory muscles. The state of the vocal system is determined by physical laws and the interaction of the different determinates. We have looked at the role of tranglottal pressure, which is the difference between the subglottal and supraglottal pressures, and we have studied the change in [F.sub.0] per unit change in transglottal pressure (dF/dP) using a shutter valve, which changes the transglottal pressure. We found that the relationship between [F.sub.0] and dF/dP is characterized by a V-shaped curve with a nadir around 200 Hz in adult males. (1) This nonlinear relationship was examined further using a rubber model, and we suspected that left limb, the downward side of V, is predominantly determined by the vocal fold's length, and right limb by the vocal fold's mass. However some questions remain. For example, no clear relationship between elongation of the rubber section that simulates the vocal fold and a negative dF/dP value was seen, as occurs in adult men. (2) Kataoka and Kitajima (3) also measured dF/dP in three dogs, but they failed to find a negative dF/dP. In addition to the three accepted parameters that determine [F.sub.0], length, stiffness, and subglottal pressure, we added one more item. The vocal tract usually is considered an articulatory organ. However, the interaction of the vocal fold oscillations and its acoustic load is known as the source-tract effect. The glottal volume velocity versus time curve changes slowly initially then rapidly accelerates. (4) Therefore, the study of the role played by the vocal tract in determining dF/dP is a very interesting topic. In the present study, we measured the dF/dP in six men using two different artificially lengthened vocal tracts, in which the acoustic characteristics were altered.

SUBJECTS AND METHODS

Six adult men (range, 25...

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Source Citation   

Gale Document Number: GALE|A119370746