Sparse representation of hrtfs by ear alignment

High quality spatial sound reproduction requires individualized Head Related Transfer Functions (HRTFs) with high spatial resolution. However, measuring such HRTFs requires special and expensive equipment, which may be unavailable for most users. Therefore, reproduction of high resolution HRTFs from sparsely measured HRTFs is of great importance. Recently, the spherical-harmonics (SH) representation has been suggested for performing spatial interpolation. However, the fact that HRTFs are naturally of high spatial order leads to truncation and aliasing errors in the SH representation. Thus, pre-processing of HRTFs with the aim of reducing their effective SH order is a potential solution of great interest. A recent study compared between several pre-processing methods, and concluded that time-alignment leads to the lowest SH order. However, time-alignment of an HRTF requires an accurate estimation of its time delay, which is not always available, especially for contralateral directions. In this paper, a pre-processing method based on ear alignment is presented. This method is performed parametrically, which makes it more robust to measurement noise. Evaluation of the method is performed numerically, showing significant reduction in the effective SH order and in the interpolation error.