Re: HRTF failure (Brian FG Katz )

Subject: Re: HRTF failure
From:    Brian FG Katz  <brian.katz@xxxxxxxx>
Date:    Sun, 16 Nov 2008 22:24:52 +0100

Christian, While there now seems to be a number of comments responding to your question, I though that I would add a few more, as I think there are some things which need to be considered. First, there has been some discussion now about headphone choice and equalization. While this is important for coloration considerations when trying to create a true-to-life recreation of a given sound source, for strict localization it is less important. In addition, you test seems to concentrate on the horizontal plane, and not vertical, where spectral cures are more crucial. We have recently presented a paper examining the importance of headphone choice/equalization and it is not the as important as some may state. As you are already using a generic HRTF, there will already be coloration by the pinnae which differs from the actual individual. D. Schonstein, L. Ferré and B. Katz, “Comparison of headphones and equalization for virtual auditory source localization.” Proceedings of the 155th ASA, 5th Forum Austicum, & 2nd ASA-EAA Joint Conference, Paris, 29Jun-6Jul 2008. Second, are the comments regarding head-tracking. It is sure that localization improves greatly with head tracking, and the lack of can pose some errors, with front/back confusions being a serious effect. While adding tracking is good for rendering, it rarely falls into the possible realm for many studies due to the context, let alone the price. What I do note is that you are using very long sound signals (6 sec noise burst). Localization of noise bursts is predominantly dominated by the onset part of the signal, rather than the duration. Brungart I think has done some studies showing comparing pulse length and repetition number for optimal localization. We typically use 150msec bursts. As relating to head tracking, if the pulses are sufficiently short then head-tracking adds little benefit as unintentional head-movements are not a problem. This assumes that the subject is instructed not to move of course. Third, is the question of the importance of the HRTF itself in your test. Again, as you seem to be performing a test in the horizontal plane, it is the ITD which is of great importance. You should be aware of the fact that any difference in head size between your subjects and KEMAR will result in distortions of the responses relative to this disparity. Methods exist for ITD individualization, even if you do not have an individual complete HRTF. Selecting the best HRTF for each individual from a database is a good approach for improving spectral cues, but the best spectral cues are not necessarily in any way correlated to the best ITD cues. I think much has to do with the goal of your tests, to determine where you should place you efforts. Regards, -Brian FG Katz --- Brian FG Katz, Ph.D Perception Située LIMSI-CNRS BP 133 F91403 Orsay France tel. (+33) fax. (+33) direct.(+33) e-mail Brian.Katz@xxxxxxxx web_theme: web_group:

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