On 01/22/2011 11:56 PM, f...@kokkinizita.net wrote:
On Sat, Jan 22, 2011 at 04:38:19PM +0000, Augustine Leudar wrote:
Im sure Im missing something obvious here but humour me. With a stereo
signal I can just place two speakers in a line and have my stereo signal
send two discrete channels to each speakers, each channel representiong one
channel of my stereo microphone. The same with quadrophonic (with no
matrixing nonsense) - four mics go to four speakers placed in a square -
works fine, tried it hundreds of times, no decfoding involved.
well, it demonstrably does *not* work fine.
i'd go as far as saying it doesn't work at all. it may sound ok in some
cases, but it won't do the job (of producing an auditory event for the
listener that matches the original sound event).
unless, like fons remarked, you make the microphones precisely
co-incident, and even then the result will be sub-optimal.
Why cant you
do the same for 3 dimensianal sounds ?
you can. if you're happy with the performance of this approach in the
horizontal case, the same approach will fail to work in just the same
way for full 3d :)
Four mics surround sending discrete
channels to four spekers placed in a square and one for height information
going to a mic above your head - this should naturally represent the sound
field without any decoding , Ive done this and it has been quite effective
- so why the need for elaborate and expensive decoding ?
what if i'm being nasty and put my speakers somewhere else? such as, one
in front, two at +/-30 and +/-110 (ok, that would be a really sick and
utterly nonsensical thing to do, i'm just trying to make a point here).
i have tried to deal with questions similar to yours in a recent
tutorial at the tonmeistertagung. i'm not 100% happy with the result and
will probably receive death threats from serious mathematicians, but for
a "from scratch" explanation of what ambisonics is and why it might be
useful, try these (rather verbose) slides (you can ignore the last part,
which is just a project report):
http://stackingdwarves.net/public_stuff/linux_audio/tmt10/TMT2010_J%c3%b6rn_Nettingsmeier-Higher_order_Ambisonics-Slides.pdf
the full paper has some more examples in it, but it's a bit weird as it
tries to convey a "gut feeling" for the mathematical foundations. not
sure if that succeeded:
http://stackingdwarves.net/public_stuff/linux_audio/tmt10/TMT2010_J%c3%b6rn_Nettingsmeier-Higher_order_Ambisonics.pdf
best,
jörn
--
Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister für Veranstaltungstechnik (Bühne/Studio), Elektrofachkraft
Audio and event engineer - Ambisonic surround recordings
http://stackingdwarves.net
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