Spherical Harmonic Spectra of Head-Related Transfer Functions
Head-Related Transfer Functions (HRTFs) represent the filtering that sound signal is subjected to between its source at a particular spatial location and its detection at the ears. Encoded into a set of HRTFs are the acoustic cues which our auditory system will use to perceive the sound signal as emanating from a particular location. Previous papers have developed a continuous model of human HRTFs by expressing each bin of the magnitude spectra in the form of a weighted sum of surface spherical harmonics. In this paper we examine the significant and potentially insightful variations in the amplitudes of each spherical harmonic weight, as we move along the audio spectrum. We make use of representations known as Spherical Harmonic Spectra (SHSs) to illustrate these weight variations, and discuss the implications of the representation in terms of identifying physiological variations within the HRTFs, and in terms of the efficient measurement and encoding of HRTF data.
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