Experimental data is available for the Head Related Impulse Response (HRIR)
for several azimuth and elevation angles, and for several subjects. The
measured HRIR depends on several factors such as reflections from body parts
(torso, shoulder and knees), head diffraction, and reflection/diffraction
effects due to the external ear (pinna). Due to the combined influence of
these factors on the HRIR, it is difficult to isolate features thought to be
perceptually important (such as the frequencies of pinna spectral notches)
using standard signal processing techniques. Signal processing methods to 
extract the frequencies of the pinna spectral notches from the HRIR are
presented. The techniques are applied to extracting features from the
publicly available CIPIC HRIR database. A brief discussion relating the
notch frequencies to the physical dimensions and the shape of the pinna is
given.
UMIACS-TR-2004-51