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Re: HRTF failure
If you interpret the pattern in your GIF plot as
a pair of big "X" patterns, you can see it
represents primarily a front-back confusion.
This is very typical with headphone listening.
There is lots of literature on this particular
difficulty and ways to improve it:
At 11:43 AM +0100 11/14/08, Christian Kaernbach wrote:
We encounter a problem when trying to place a
sound at a virtual position in space by means of
head related transfer functions (HRTF).
We use sounds from the IAPS database
(International Affective Digitized Sounds
System, Bradley & Lang) as well as simple white
noise of six seconds duration. We use the Kemar
HRTF, the "compact data" with zero elevation. We
convolve the original sound data with the HRTF
data as suggested in the documentation. The
final sounds are presented using Beyer Dynamic
We have tested the precision with which our
sounds are placed in virtual space, by
presenting them to eight listeners. The
listeners had a touchscreen lying on their lap,
with a circle plotted on it, and they could
indicated the direction where they perceived
that the sound came from. We presented to them
in total 144 sounds, 72 noises and 72 IAPS
sounds, coming from 36 virtual directions (0°,
10°, 20°...) in randomized order.
The results are shown in a figure that I put in the internet:
The red dots are from IAPS sounds, the yellow
dots are from the noises. The x-axis shows the
"true" (virtual) angle, the y-axis shows the
estimated angle. As can be seen in this figure,
listeners could well discriminate between sounds
from the left and sounds from the right. But not
more than that. There is a certain reduction of
variance for sounds coming from 90° and from
270°, but there is no correlation with angle
within one hemifield.
Now we are eager to learn from you: What could be the cause for this failure?
A) HRTFs are not better than that.
B) The headphones are inadequate.
C) It must be a programming error (we don't think so)
We are grateful for any help in interpreting the
possible cause for this failure.
Thank you very much in advance,
Christian-Albrechts-Universität zu Kiel