Are spectral elevation cues in head-related transfer functions distance-independent?

Since its title, this paper addresses one of the still open questions in sound localization: is our own perception of the elevation of a sound source affected by the distance of the source itself? The problem is addressed through the analysis of a recently published distance-dependent head-related transfer function (HRTF) database, which includes the responses of a single subject on a spatial grid spanning 14 elevation angles, 72 azimuth angles, and 8 distances comprised between 20 and 160 cm. Different HRTFs sharing the same angular coordinates are compared through spectral distortion and notch frequency deviation measurements. Results indicate that, even though the independence of spectral elevation cues fromdistance of the source can be assumed for the majority of all possible source directions, near-field HRTFs for sources close to the contralateral ear or around the horizontal plane in the ipsilateral side of the head are significantly affected by distancedependent pinna reflections and spectral modifications.