One-dimensional and three-dimensional propagation analyses of acoustic characteristics of Japanese and French vowel /a/ with nasal coupling

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In this paper, we describe a comparison of the acoustic characteristics of one-dimensional and three-dimensional models of vocal tracts with nasal coupling. One-dimensional acoustic propagation is computed using an electric analog model. A finite element method is used for three-dimensional acoustic simulation. The comparison of these two approaches involves the vocal-tract shape of two subjects, one Japanese male and one French male pronouncing the vowel /a/ in their native language. Results show that the pole/zero pairs ascribed to the nasal coupling for both simulations appeared at almost the same frequency, at least below 2 kHz. Little difference between the one-dimensional and three-dimensional simulations in the transfer functions for the French subject is observed, since the three-dimensional mesh for the French subject is smoother. An extra pole exists in the transfer function of the three-dimensional model for the Japanese subject, possibly caused by the asymmetric structure of the laryngeal cavity. In the three-dimensional distribution of the active sound intensity vectors for the French subject, sound energy fluxes circulate between oral and nasal cavities coupled in the vicinity of the lips and nostrils.