Numerical study on source-distance dependency of head-related transfer functions.

This paper investigates the source-distance dependency of head-related transfer functions (HRTFs) on the horizontal and median sagittal planes using the boundary-element method and a dummy head scanned with laser and computer tomography scanners. First, the HRTF spectra are compared among various source positions in a head-centered coordinate system, confirming that the major HRTF spectral features vary with source distance as stated in previous works. Furthermore, the HRTF spectra are compared in an ear-centered coordinate system, revealing how the outer ear angle of incidence affects the source-distance dependency of the HRTFs. Next, the comparison across coordinate systems reveals that the source-distance dependency of the ipsilateral HRTFs on the horizontal plane is mainly attributable to the outer ear angle of incidence, whereas the contralateral HRTFs vary with the source distance mainly due to the head's presence. Finally, results also show that, in an ear-centered coordinate system, the ipsilateral HRTFs do not depend strongly on a source distance greater than 0.2 m from the center of the head, whereas the contralateral HRTFs depend on source distance less than 1.8 m. Results also show that HRTFs on the median sagittal plane depend on a source distance of less than 0.4 m.