The effect of pinna filtering in binaural transfer functions on externalization in a reverberant environment

The perception of the externalization of noise stimuli is investigated with respect to the pinna filtering effect on direct and reverberant parts of binaural transfer functions. Individual binaural room impulse responses (BRIRs) recorded with and without pinnae, called pinna BRIRs and head BRIRs respectively, are divided into the direct and reverberant parts. For frontal and lateral sources, four types of BRIRs are constructed and investigated. Two of them are measured on subjects with their pinnae exposed or not, and the other two are obtained by concatenating the direct and reverberant parts of the two types of measured BRIRs crosswise. Normal hearing listeners are presented with noise trains convolved with these four types of BRIRs. It is found that pinna filtering in the direct parts is helpful for externalization while pinna filtering in the reverberant parts produces less externalized sound images. Further analysis shows that pinna filtering can change the direct-to-reverberant ratio (DRR), the frequency-to-frequency variability (FFV), and the interaural coherence (IC). The DRR and the FFV are only partially related to the externalization ratings, but the short-term IC corresponds well to the ratings. This study provides guidance for improving externalization perception in binaural synthesis.