Formant transition of nasal and liquid in the external auditory canal

Abstract

Objectives: While speech sounds can be heard and understood through the external ear (EE), the EE transmits the sound through the air as a medium. Consequently, acoustic characteristics of speech sounds differ depending on the structure of the EE or the physical characteristics of the medium. This study aims to investigate how the characteristics of the EE's acoustic transmission affect the formant transition (FT) of nasals and liquids. Methods: Sixteen healthy men and women who had no problems in their auditory or articulation system participated in this study. One participant acted as the speaker, and the remaining 15 participants were listeners. In terms of the voice, monosyllabic words which combined the nasal /n/ and liquid /l/ with the vowel /a/ were used. When recording, a high-performance microphone was used, and mounted on the upper pinna and the external auditory canal respectively. The recorded voice was calibrated with MATLAB, and the FT was analyzed with Praat. The differences between the two voices were analyzed with a two-way ANOVA. Results: In the sound field, the FT was elevated for both nasals and liquids with the exception of F4 which showed an increase following a decrease. In the EAC, regarding the formant transfer, only F1 and F2 exhibited an elevation, while F3 decreased, and F4 was maintained in the case of nasals. In the case of liquids, it was observed that although F1 and F4 were elevated, F4 was nearly horizontal, F2 showed a decrease, and F3 was maintained. Conclusion: The formant transition of the external auditory canal contributes to improving the discriminative qualities of speech by broadening the formant spacing of nasal F3, F4, and liquid F2, F3, and F4.