Howdy All (Authentic Western Greeting):
I have to add my two bits on "How not to advertise binaural." I've heard the
barbershop demo as well as a plethora of the more ubiquitous helicopter demos.
My delicate and politically correct way of putting it is this: They all suck,
and in more ways than one.
I got into Ambisonics because people doing peer-reviewed studies on hearing
were using equally-crappy stimuli to study, in a laboratory environment,
various processing strategies for cochlear implant and hearing aid devices. At
least the sentences (e.g. IEEE 5-word sentences) weren't providing cognitive
clues. I've been a proponent of providing the physical reconstruction of waves,
and letting the listener use subtle cues such as head movements to determine
sound-source direction, distance, or clarity. Physical realism shouldn't
include psychoacoustical clues such as ILDs or ITDs until you stick a head
(plus brain) into the acoustical environment; i.e. let the brain, person, or
processor act on the physical space. Don't create stimuli (at least for
legitimate research) that includes such clues unless you're studying effects of
a particular parameter. Nothing's going to be perfect in the lab, but wave
field synthesis, Ambisonics, etc. provide a way of
capturing a dynamic environment (compared to stand-alone monaural sources
arbitrarily panned around the room). I've used HRTFs and IRs as a way of
(poorly) demonstrating the potential of Ambisonics, but fear that I've done an
injustice in the process.
I use EAR insert earphones (which totally obliterate ear canal resonance--which
is good if KEMAR already accentuated them!), Sennheiser HDA 200 audiometric
phones (great for estimating SPL based on voltage level for the average
listener), AKG studio phones, and Sony DJ phones. All give a different
presentation that goes beyond tonal characteristics or timbre. But back to
those binaural and transaural demos...
When it comes to binaural demos, parts of sounds remain in-the-head, whereas
other components of the auditory scene move about as they should. In the end,
they amuse and captivate first-time listeners, but that's about it. I heard one
transaural demo that wasn't at all bad, but the sweet spot was so small that
shifting position in a chair threw the illusion off. For me, sound in space
from a surround of loudspeakers rules. This isn't portable, so giving a demo of
Ambisonics requires that the listener has access to the requisite equipment.
Hard to find those listeners...
Best to all,
ELC
Eric Carmichel
Cochlear Concepts
I take full responsibility for my opinions, and have eaten my words more than
once.
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