HRTF: azimuth to ITD

[JOHN WOODRUFF <woodruff.95@xxxxxxx>]

i am doing some work that involves head-related transfer functions.  i have been using the MIT and CIPIC databases and have noticed some unexpected results regarding interaural time delay.  for example, in the case of the MIT database (full,L) at 0 degrees elevation, the time delay associated with the HRTF of 70 degrees azimuth is smaller than that of 65 degrees azimuth for 80-150 Hz.  similarly, for 6.5-8 kHz, the time delay for 70 degrees azimuth is larger than that of 75 degrees azimuth.  

i have noticed similar trends in the compact MIT database and in the CIPIC database.  i can imagine that HRTF measurements taken from humans may have slight discrepancies due to subtle head movements by the subject, but can anyone explain why measurements using KEMAR would have non-monotonic functions relating azimuth and ITD?  does what i'm seeing reflect physical time delay or is it possibly an artifact from the measurement process or signal processing involved?  

thanks very much, john


********************************
John Woodruff
Perception and Neurodynamics Lab
Ohio State University
www.cse.ohio-state.edu/~woodrufj