The role of spatial detail in sound-source localization: Impact on head-related transfer function modeling and personalization

Abstract

Current techniques designed to personalize generic head-related transfer functions (HRTFs) have some capacity to quickly customize spatial auditory displays, but these techniques generally fall short of the level of realism and performance provided by fully individualized HRTF measurements. This residual performance deficit reflects inaccuracies due to vast amounts of spatial and spectral variation that occurs across the measured HRTFs of individual listeners. Some of this variation encodes perceptually-important directional information, but a substantial proportion does not. Kulkarni and Colburn (1998) showed that perceptually irrelevant spectral variation could be eliminated by smoothing the HRTF magnitude with a truncated Fourier-series expansion. The present study investigates a related method for smoothing the spatial variation contained in the HRTF by utilizing a truncated spherical harmonic expansion. The impact of spatial smoothing was evaluated by comparing localization performance with individualized HRTFs which were fully represented or had various degrees of spatial smoothing. Results indicate that a highly-smoothed fourth-order spherical harmonic representation can produce localization accuracy comparable to that of a full individualized HRTF. Analysis of the resulting simplified HRTF representations also uncovered a number of interesting relationships across different individuals which may provide new insights for the development of future HRTF personalization and estimation techniques.