Comparison of Vocal Tract Resonance Characteristics Using LPC and Impedance Measurements

Authors: Stoffers, J.; Neuschaefer-Rube, C.h.; Kob, M.

Source: Acta Acustica united with Acustica, Volume 92, Number 5, September/October 2006 , pp. 689-699(11)

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Acta Acustica united with Acustica, published together with the European Acoustics Association (EAA), is an international, peer-reviewed journal on acoustics. It publishes original articles on all subjects in the field of acoustics, such as general linear acoustics, nonlinear acoustics, macrosonics, flow acoustics, atmospheric sound, underwater sound, ultrasonics, physical acoustics, structural acoustics, noise control, active control, environmental noise, building acoustics, room acoustics, acoustic materials, acoustic signal processing, computational and numerical acoustics, hearing, audiology and psychoacoustics, speech, musical acoustics, electroacoustics, auditory quality of systems. It reports on original scientific research in acoustics and on engineering applications. The journal considers scientific papers, technical and applied papers, book reviews, short communications, doctoral thesis abstracts, etc. In irregular intervals also special issues and review articles are published.
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Abstract:

The application of acoustic impedance measurements offers a non-invasive way of identifying the resonance characteristics of the vocal tract, in normal speakers as well as in patients with an altered vocal tract configuration. Similar methods have been successfully used to train pronunciation of foreign vowels or for the analysis of high-pitched soprano voices. The aim of this study is applying the impedance method to patients with diseases of the vocal tract in order to characterise the extend of disorder and, as a future application, to provide a practical tool for therapeutic treatment of articulation problems which is independent of the voice source. Whereas a conventional LPC analysis is successful only when applied to more or less stationary voice signals, an external excitation with subsequent measurement of the vocal tract impedance at the mouth can give reliable results when the voice source is not stable or even missing. Simultaneous LPC and impedance measurements of the 5 sustained vowels /a:/, /ε:/, /i:/, /o:/, /u:/ and the phonemes /l:/ and /x:/ were performed in a group of 36 female and 46 male healthy speakers. Similar to the formant calculation from the LPC data, an evaluation of the impedance measurements was carried out to characterize the impedance curves and thus derive similar values for frequency, amplitude and bandwidth. Case studies of two patients with severe morphological alterations of the vocal tract are carried out of which the impedance measurements show a significant resonance shift in some vowels compared to the normal group.

Document Type: Research article