Directional information in head related transfer functions

The synthesis of spatial sound, which is played through the headphones, can be done by the use of head related transfer functions (HRTF). The latter describe the changes in the sound wave as it propagates from a spatial sound source to the human eardrum. The functions include many different factors, which influence the accuracy of spatial sound source perception. The most important factors are inter-aural time difference (ITD), inter-aural level difference (ILD) and the spectral changes for different spatial positions. The main goal of our research was determining with the aid of principal component analysis (PCA) the spectral variation important for the perception of direction. We concentrated on the azimuth perception in the horizontal plain. PCA was applied to HRTF linear amplitude spectra, thus excluding the phase spectrum and ITD. The analysis assembled all spectrum variations important for the azimuth perception in the first and partially second PCA weight variation. The hypothesis was tested on and confirmed by 15 test subjects who preformed the virtual sound sources localization tests