Improving sound spatialization by modifying head-related transfer functions to emulate protruding pinnae

Head-related transfer functions (HRTF) are widely used for the synthesis of binaural sound, which can produce in the listener the illusion of a sound that originates at a virtual location around him/her. The accuracy in the perception of these sounds, however, is compromised by the "cone of confusion" effect. Due to this effect, a source in the back hemisphere is perceived to be in the front hemisphere, and vice versa. This effect is particularly noticeable in the front (azimuth 0°) and the back (azimuth 180°). Preliminary observations suggested that the HRTF of individuals with particularly protruding ears show more accentuated spectral differences between symmetric locations. These HRTF were helpful in resolving the cone of confusion when used by subjects with average or small pinna protrusions. This paper describes the design of attenuation/amplification spectral profiles based on those seen in HRTF from protruding ears and how they are applied to modify the HRTF of several subjects. Listening tests showed that the HRTF so modified yielded enhanced front-back differentiation, with respect to the original HRTF of the test subjects