[vorbis-dev] Multichannel Encoding

Marshall Eubanks tme at 21rst-century.com
Fri Jan 26 09:52:35 PST 2001

Gerry wrote:

> .. just a little thought ..
> Humans have two ears. Direction of sound is determined by the brain by (1)
> calculating the difference in time and figuring out the way this sound came
> from (actually this is used in some new kinds of IQ-tests to test the brains
> "performance" :) ), and (2) frequency decoding in the ears, where sound from
> different locations get some kind of frequency coding by letting the sound
> bounce around a little in the outer part of the ear (so if we just had holes
> for ears, we wouldn't be able to do this).

Don't forget amplitude differences between the ears (and as we move our ears).

> Now, here's the thought: Considering all of this, it should, in theory, be
> possible to create perfect surround sound in just two channels, one for each
> ear. This would obviously not work for normal loudspeakers (unless some
> advanced frequency-coding to compensate for the ear's own happened, but
> still you have the problem with the brain-calculated time-difference). For
> earplugs and such it should work perfectly though. A problem might be that
> every human has different ears (so the frequency coding is slightly
> different), but still, it should be possible. Any thoughts ?
> Gerry

Hello Gerry;

There is also what in radar is called "aperture synthesis" - i.e., we turn & move our heads. (This breaks, for example,
the front back 180 deg ambiguity unless you hold really still). The brain clearly uses this to
help figure out sound directions. So I don't think you could do it
for two loud speakers, even in principle.

For earphones, I have heard of VR work where the attitude of the 'phones is measured and the
signal to each ear is changed in real time to replicate what you would have heard in open air
if you turned your head the same way. My guess is you could do a pretty good surround sound this way, but
it would take a fair amount of CPU on the client side.

                                 Marshall Eubanks

T.M. Eubanks
Multicast Technologies, Inc
10301 Democracy Lane, Suite 410
Fairfax, Virginia 22030
Phone : 703-293-9624
Fax     : 703-293-9609
e-mail : tme at on-the-i.com     tme at multicasttech.com

http://www.on-the-i.com http://www.buzzwaves.com

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