Lateral excitation of a vocal tract analog

Abstract

A schematic mechanical analog of the vocal tract was constructed, consisting of a cascade of 21 adjustable‐width rectangular cross‐sections of 8‐mm length each. Side openings spaced at 25.4‐mm intervals along the tube permitted the excitation of the tract by a standard hearing aid driver, mounted flush with the internal wall, at any one of seven locations from “glottis” to “lips.” The tract was adjusted to simulate the area functions of several American vowel sounds estimated directly from the speech wave [H. Wakita, Speech Commun. Res. Lab. Monogr. No. 9. (1972)]. The periodic excitation waveform resembled a glottal pulse train; the radiated sound was picked up by a condenser microphone in front of the “lip opening.” Waveshapes and spectra were recorded and formant characteristics measured. Fairly good agreement with the norm was noted in the frequency region up to about 800 Hz. Deviations at higher frequencies can be attributed to the violation of the plane wave propagation usually assumed for the acoustic tube model. This work is part of a collaborative effort (with Dr. Robert J. Hanson of the UCSB Speech Department) to develop a speech support system for laryngectomees. [Project supported by the American Cancer Society, Inc.]