On the relation between pinna reflection patterns and head-related transfer function features

This paper studies the relationship between head-related transfer functions (HRTFs) and pinna reflection patterns in the frontal hemispace. A pre-processed database of HRTFs allows extraction of up to three spectral notches from each response taken in the median sagittal plane. Ray-tracing analysis performed on the obtained notches' central frequencies is compared with a set of possible reflection surfaces directly recognizeable from the corresponding pinna picture. Results of such analysis are discussed in terms of the reflection coefficient sign, which is found to be most likely negative. Based on this finding, a model for real-time HRTF synthesis that allows to control separately the evolution of different acoustic phenomena such as head diffraction, ear resonances, and reflections is proposed through the design of distinct filter blocks. Parameters to be fed to the model are derived either from analysis or from specific anthropometric features of the subject. Finally, objective evaluations of reconstructed HRTFs in the chosen spatial range are performed through spectral distortion measurements.