On the spatial symmetry of head-related transfer functions

The spatial symmetry of head-related transfer functions (HRTFs) in the horizontal and median planes was investigated using an asymmetry coefficient derived from cross-correlation analysis. Statistical results from 52 human subjects show that, for an asymmetry coefficient below 0.05, the horizontal-plane HRTFs are approximately left–right symmetric below 5.0 kHz and 1.1 kHz for ipsilateral and contralateral source directions, respectively, whereas the frequency limit is 5.5 kHz for the median-plane HRTFs. For the horizontal-plane HRTFs, the front-back asymmetry coefficient is often greater than the left–right asymmetry coefficient. Moreover, a series of psychoacoustic experiments was conducted to evaluate the audibility of the left–right asymmetry of HRTFs in the horizontal and median planes separately. The experimental results show that the left–right asymmetry of HRTF above 4 kHz is perceivable for most source directions.