The effect of elevation on ITD symmetry

In binaural simulations, Head-Related Impulse Responses are used to recreate a 3D auditory display through headphones. Public repositories of individually measured HRIRs are widely used in industry and research. However, head-related anthropometric asymmetries, among measured subjects, are a likely cause of measured asymmetries in Interaural Time Delay cues (ITDs), which may lead to imprecise sound localization. As part of a larger study on HRIR personalization, this paper expands, to the elevation dimension, the investigation of ITD asymmetry in public databases of measured HRIRs. In a previous exploratory study, concerning the horizontal plane only, a region of sensitivity, where the ITD asymmetry was observed to be significantly more prominent, was identified in datasets of individually measured HRIRs approximately between the azimuth range of θ = ±90° to ±130°. For this paper. two publicly available databases of individual HRIRs were selected and analyzed in search of an elevation effect on ITD symmetry. Results found that an increase or decrease in elevation angle φ, away from the horizontal plane, affects the asymmetry curve by reducing the gap between average and peak ITD asymmetry values within the mentioned region in a roughly linear trend. This finding points to the fact that, within the examined datasets, the statistical presence of ITD asymmetries is gradually less severe, although still present, as the elevation angle moves away from the horizontal plane.