Jianwu DANG, Kiyoshi HONDA, Hisayoshi SUZUKI
Morphological and acoustical analysis of the nasal and the paranasal cavities
Abstract:Morphological measurements of the nasal and paranasal cavities were measured to investigate on acoustic properties of the human nasal tract. The magnetic resonance imaging (MRI) technique was used to measure the three-dimensional geometry of the vocal tract. The area function of the nasal tract was calculated for seven subjects using natural breathing. The entire vocal tract was measured for five subjects during sustained production of nasal consonants. A marked morphological difference was observed between our data and previously published data particularly in the middle portion of the nasal tract. Previous data derived from cadaver specimens indicated a wide cavity in the middle portion possibly due to absent or dehydrated mucous membrane, while our data showed narrow passages caused by thick mucosa. It has been confirmed by experiment that the wide cavity is reproducible by applying an adrenaline-like agent inside the nose. Transfer functions of the vocal tract and the nasal tract were calculated from measured data, and compared to spectra of real speech signals recorded subsequent to the MRI experiment. The results indicate that asymmetry between the two nasal passages can cause extra pole-zero pairs, and suggest that the paranasal cavities play an important role in shaping spectral characteristics of human nasal sounds.