APROXIMATION OF HEAD RELATED TRANSFER FUNCTION USING PROLATE SPHEROIDAL HEAD MODEL

Abstract

Researchers have used a spherical head model to construct a HRTF (Head Related Transfer Function), which has a single adjustable parameter (radius of head) for HRTF customization mainly because of its simplicity. In this paper, we suggest a mathematical form to calculate analytic spheroidal HRTF for an incident point source. From this mathematical transfer function, a spheroidal head model can be used for near-field HRTF customization with adjustable two parameters (head width and head height). Moreover, by using the proposed mathematical form, analytic spheroidal HRTFs can be computed even in high frequencies without computational difficulties. To see the necessity of head height consideration, two analytic solutions, those are classical spherical HRTF and proposed spheroidal HRTF, are compared with measured HRTF for a KEMAR (Knowles Electronic Manikin for Acoustic Research) dummy. By varying head dimensions and ear offsets, ITD (Interaural Time Difference) surfaces were approximated from ray-tracing formula. Through optimization procedure, we found an optimal ITD surface which minimizes ITD estimation error between the estimated ITD and measured ITD surfaces. In the view point of ITD, there are only slight differences between ITD optimized spherical and ITD optimized spheroidal head model. In the view point of spectral information, however, notch frequencies of ITD optimized spheroidal HRTF and measured HRTF show similar patterns at the contralateral position and low frequencies.