Horizontal-plane HRTFs of KEMAR mannequin spatially interpolated with a resolution of 0.5°

HRTFs of the KEMAR manikin (Gardner and Martin, 1995):

• "hrtf_M_normal pinna.sofa": the original HRTF dataset from the KEMAR manikin at a lateral resolution of 5° stored as a SOFA file (Majdak et al., 2013)
• "hrtf_M_normal pinna resolution 0.5 deg.sofa": A super-resolution HRTF set with a directional up-sampling of the original HRTF set to the lateral resolution of 0.5°. To this end, for each ear's HRTF set:
  • The broadband timing was removed by replacing the HRTF's phase spectrum by the minimum-phase spectrum (Oppenheim et al. 1999) corresponding to HRTF's amplitude spectrum.
  • For the interpolation of the amplitude spectra, the complex spectra of the minimum-phase HRTFs for two adjacent available directions were averaged according to a weighting that corresponded to the interpolated target direction. 
  • For the interpolation of the timing, a continuous-direction model of the time-of-arrival (TOA) was applied (Ziegelwanger & Majdak, 2014). TOA is the broadband delay arising from the propagation paths from the sound source to the listener's ear. For a given direction of a sound, the interaural difference of TOAs corresponds to the ITD. The TOA model parameters describe listener's geometry (head and ears) and configure a continuous-direction function of broadband TOA. We used this function to calculate TOAs for directions in steps of 0.5°. To this end, for each ear, the model was fit to an HRTF set as described by Majdak & Ziegelwanger (2013) using the implementation from the Auditory Modeling Toolbox (Søndergaard & Majdak, 2013). Then, each minimum-phase HRTF was temporally up-sampled by a factor of 64, circularly shifted by the TOA obtained from the continuous-direction TOA model for the target direction, and then down-sampled to the sampling rate of 44.1 kHz. Note that the temporal oversampling was required to achieve an interaural resolution of 0.35 µs.