The following are answers to some of the questions that were raised during the course of our seminar on Spatial audio. We would appreciate any comments/suggestions. You can contact us via email at dturaga@ece or alkanhal@ece .
Ans. These can be found at the following site. They are not organized too well, but these are the best notes we could find on the web.
Ans. Surprisingly, we have not been able to locate any information regarding this. However, it is quite reasonable to assume (as was pointed out by Prof. Chen in class) that the current systems exploit only the second class of auditory cues (i.e. intensity) for sound localization and do not take into account the first class of cues (Transfer function of the outer ear, head and shoulder).
Ans. The answer is taken from Wightman, Kistler, "Headphone simulation of free-field listening.I ", J. Acoust. Soc. Am. 85(2), Feb. 1989.
The approach is based on well-understood linear filtering principle.
Let:
x1(t) represent an electrical signal that drives a loudspeaker
in free field.
y1(t) represent the resultant electrical signal from a probe microphone
positioned at a listner's eardrum.
x2(t) represent an electrical signal that derive the headphone,
where
y2(t) the resultant microphone response.
Given x1(t), our goal is to produce x2(t) such that y2(t)
equals y1(t).
We do this by designing a linear filter that transforms x1(t)
into x2(t).
The design is described in the frequency domain (X1(jw),
X2(jw), Y1(jw), Y2(jw) are the frequency
transforms of x1(t), x2(t), x3(t), x4(t)).
We know
We also know
Ans. We couldn't find detailed information on the holophoinic
technology, but from the information that is available on the web site
http://www.holophonics.com
it seems to be a new approach for 3D audio. On the other hand, some people
believe nothing is special with the holophonics. They think of it as the
same as the binaural technology. For such an opinion, you can refer to
http://www.cs.colostate.edu/~meier/floyd/echoes4.html#5.1.
Here is a summary of what holophonics has said about its technology and
you can go to its web site for more information.
1. It uses a special holophonics head "Ringo" and an associated processing
unit for recordings " No details. They are secretive". This technique is
used to capture the full spectrum of essential information travelling from
the ear to the brain in the recording environment.
2. It works very well with speakers and requires no decoding. Initial
tests show that the 3D space in the movie theater is 10 times more realistic
with Holophonics than with current surround sound.
3. This technology is based on a new understanding of the physiology of human hearing, and this new knowledge doesn't base on that we receive a sound in a passive manner "It doesn't base on the Head Related Transfer Functions". It bases on that human ear generates its own reference tone which interferes with incoming sound to create the necessary spatial information.
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