A psychophysical evaluation of near-field head-related transfer functions synthesized using a distance variation function.

A method for synthesizing near-field head-related transfer functions (HRTFs) from far-field HRTFs measured using an acoustic point-source of sound is presented. Near-field HRTFs are synthesized by applying an analytic function describing the change in the transfer function when the location of a sound source changes from the far-field to the near-field: the distance variation function (DVF). The DVF is calculated from a rigid sphere model and approximates the change in the frequency-dependent interaural level cues as a function of the change in sound source distance. Using a sound localization experiment, the fidelity of the near-field virtual auditory space (VAS) generated using this technique is compared to that obtained by simply adjusting the intensity of the VAS stimulus to simulate changes in distance. Results show improved distance perception for sounds at simulated distances of up to 60 cm using the DVF compared to simple intensity adjustment, while maintaining directional accuracy. The largest improvement for distance perception were for sound sources located to the side and within 40 cm. When intensity was removed as a cue for sound source distance from near-field sounds generated using the DVF, results showed some discrimination of sound source distances but, in general, distance perception accuracy was poor.