delta filters the phase difference between the right and left ear is automatically taken into account since we add and subtract the original ipsolateral and contralateral hrtfs research carried out since the 1960 39 s see blauert 2 blauert 3 shaw and teranishi 12 and wright et al 13 indicates that the auditory localizing system is organized into preferred bands of frequencies which are dependent on the angle of incidence of the source of sound thus it is important when approximating the measured hrtf to pay particular attention to these spatial localizing intervals these preferred bands can be shown to be characterized by notches and peaks caused by sound diffraction around the head and reflection caused by the torso and pinnae this diffraction and local reflections from the folds of the pinnae cause peaks and notches to appear in the hrtf because the pinna 39 s shape and its complex structure of folds varies for each individual the hrtf is listener dependent but nevertheless general spectral trends can be seen although there is variation among individuals 39 hrtfs there exist certain spectral similarities that can be identified it is known that these spectral trends enable different listeners to obtain spatial cues that utilizing other individuals 39.