Hi Eric.
Thanks for the post, and yes, it makes a lot of sense regarding
differing perceptions when auditioning binaural material.
I think IRCAM have identified (at least) several different "types" of
ears in relation to binaural perception. At least that was the
information they gave me when I was discussing it with them in October
last year.
Best regards,
Haig
On 14/01/2012 7:10 AM, Eric Carmichel wrote:
Hi Dave,
I just wished to add my two bits regarding binaural listening and the rearward
illusion you experience. Having investigated the effects of binaural electronic
hearing protectors on localization, I do recall two sources of information (in
addition to my own) where listeners experienced a rearward illusion of sound
sources. The studies had to do with hearing protection devices (HPDs), but
aspects of the studies apply to binaural listening in general. Of course,
retaining head and pinna cues is what we desire with binaural recordings, but
one man’s HRTF is another man’s, well...? In one of the (HPD) studies, pinna
cues were absent because of occlusion, and this was believed to account for a
rearward illusion. The references are
Russell G, Noble WG. Localization response certainty in normal and disrupted
listening conditions: Towards a new theory of localization. J Aud Res 1976; 16:
143-50
Oldfield SR, Parker SP. Acuity of sound localization: A topography of auditory
space: II, Pinna cues absent. Perception 1984; 13: 601-17
For Russell and Noble, it was believed that loss of canal resonance accounted
for a rearward illusion (this was for listeners wearing earplugs). Under
earphones, things are different. For example:
In my study*, it was easy for subjects’ to discern left-from-right sound source
location but discrimination between left rear and left front (or right rear and
right front) was difficult. Front-back reversals accounted for the largest
percentage of errors. Most errors made for the HPD conditions occurred at 120
degrees and 240 degrees (rear plane) and sounds coming from these locations
were often judged as coming from 60 and 300 degrees (front plane),
respectively. One listener, however, made localization errors opposite from
other listeners. For this listener, regardless of condition, more ipsilateral
errors were made to sounds coming from 0 degrees than for sounds coming from
180 degrees. Localization under HPDs for this listener was also unique: Stimuli
presented at 60 and 300 degrees were often judged to originate from 120 and 240
degrees, respectively, which was opposite from the other listeners.
Why a frontal or rearward proclivity for any particular listener is a good
question. But it does appear that it is consistent for a given person. For me,
binaural recordings almost always seem to be in the head (despite everyone’s
best efforts), but sounds will appear to be outside of my head if they’re to
the extreme left or right and include the requisite cues (beyond ILDs). Results
from my HPD study suggested that binaural electronic HPDs retain the ILD cue
needed for lateralization (I carefully matched the gain between earcups).
However, pinna-head cues needed to make accurate front/back judgments are not
retained. According to Oldfield and Parker, such errors would be anticipated
despite stereo sound provided by the HPDs because the ITD of sound at the
tympanic membrane does not uniquely specify a location in space, only the
left/right component.
Incidentally, manufacturers’ statements for their respective binaural
electronic HPDs included
‘True ‘stereo’ for directional sound detection’
‘Stereo sound so much like your own hearing that you retain your natural sense
of sound direction’
‘…provides you with 360 degrees awareness of sound direction with the clearest
sound amplification available’
Hmmm... Check out the following and see what at least one study revealed.
*Noise& Health, October-December 2007, Volume 9. I think it cost a bit to
download; however, I won’t comment here on the cost of journal articles. If you’d
like to see a PowerPoint regarding this study, you can download it from
www.elcaudio.com/hearing/hpd_localization.pps [26.37 MB]
I presented this study (and the PP) at a colloquium: Attendees included William
(Bill) Yost and other noteworthy hearing scientists. Question: What if the same
study was repeated only using an Ambisonic surround system? I wonder whether
the same localization errors would occur. This, to some extent, might validate
the usefulness of Ambisonics in hearing research.
Another PP, for those interested in signal processing, otoacoustic emissions
and hearing physiology (not too much psychoacoustics), can be downloaded from
www.elcaudio.com/hearing/oae_study.pps [5.62 MB]
(This study was kindly rejected by JASA, but it’s still in progress.)
Kind regards,
Eric C.
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