The transfer function of the supraglottal vocal tract of the horseshoe bat, Rhinolophus hildebrandti, was obtained by a noninvasive technique, based on incremental variations in the helium content of inspired gas, which also allowed the source spectrum to be determined. The acoustic role of the vocal tract chambers was examined by obtaining the transfer function before and after filling the chambers. Simultaneous recording of sound pressures in the trachea during these experiments allowed some analysis of subglottal acoustics. With the vocal tract intact, the transfer function was found to show sharp transmission minima at the fundamental and third harmonic and a broad transmission maximum at the emitted second harmonic. This transfer function shape, along with the source spectrum obtained, demonstrates that the second harmonic dominance in the emitted pulse is achieved by vocal tract filtering, although the source spectrum is different from that typical of man in that it does not show an/-2 harmonic decay. Changes in the transfer function caused by filling the nasal chambers suggest that these structures may play an impedance matching role at the second harmonic. Filling of the tracheal chambers did not affect the transfer function but changed the tracheal acoustics in a manner which suggests that these chambers may return backward-propagated sound to the larynx with a phase shift. The possible interactive role of the nasal and tracheal chambers in increasing vocal efficiency at the second harmonic is discussed.
ASJC Scopus subject areas
- Arts and Humanities (miscellaneous)
- Acoustics and Ultrasonics