I had a feeling the first time of asking, that i'd bitten off more than i could chew, but i shall go a-googling, and at least get some sort of overview. Thanks for the input Fons, and the caution for the ambisonic political upheaval. :)<br>
<br>Alex.<br><br><div class="gmail_quote">On Sun, Jan 11, 2009 at 3:57 PM, Fons Adriaensen <span dir="ltr"><<a href="mailto:fons@kokkinizita.net">fons@kokkinizita.net</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div class="Ih2E3d">On Sun, Jan 11, 2009 at 12:56:38PM +0300, alex stone wrote:<br>
<br>
> Fons, just a follow up to the discussion about an orchestral placement<br>
> template, is there a definitive resource somewhere i can go to, and learn<br>
> more about ambisonics, and how this might help me to achieve the Holy Grail<br>
> of true placement recording?<br>
<br>
</div>The simple answer to this is 'no' :-(<br>
<br>
You can google Ambisonics of course, and you'll find some<br>
sites. Then you'll find out that information is fragmented,<br>
often contradictory, frequently outdated, and in some cases<br>
plain wrong. One of the reasons is that the technology is<br>
now well over 30 years old, at the time it was invented it<br>
was only possible to use it in its simplest forms which<br>
requires many compromises deviating from the theory, and<br>
some of these compromises have over the years established<br>
themselves as 'the thruth', confusing anyone who tries to<br>
understand things from a theoretical perspective. And of<br>
course at that time we didn't have the web. The last ten<br>
years or so have seen a renaissance of AMB research, and<br>
of course today many of the technical barriers have gone.<br>
Some people are now using up to 4th order systems routinely,<br>
and some are researching much higher orders. Today the AMB<br>
community seems to be divided in two camps, the old guards<br>
that were part of the original wave in the 70's, and a<br>
new generation of researchers that almost restarted from<br>
scratch, and is not bothered by the same legacy wisdom.<br>
Their publications (mostly PhD theses and AES papers)<br>
today provide the best information, but their approach<br>
is highly mathematical, something that can't be avoided<br>
except for the most simple cases. In between those two<br>
is part of the electro-acoustic music community which<br>
has been developing its own toolsets, most of which are<br>
incompatible with each other. I've been involved during<br>
the last half year in some 'AMB standards wars', and it<br>
has not been a very happy experience.<br>
<br>
All this should not stop you from learning about AMB, but<br>
you will find conflicting info and have to sort out the<br>
mess - you have been warned :-).<br>
<br>
First question of course is if you need it or not. If your<br>
end result is high quality surround or periphonic reproduc-<br>
tion you definitely do. If it is stereo you don't really<br>
need it, but even in that case an AMB based production chain<br>
can do some things that would be difficult to achieve in<br>
any other way.<br>
<br>
Ambisonics can be understood on many different levels,<br>
from 'intuitive' to purely mathematical. On the intuitive<br>
level, it's a way of representing the directional (not<br>
distance) distribution of sound in a 'canonical' way that<br>
is really independent of the way the sound it is captured<br>
or will be reproduced. In other words, AMB signals are not<br>
speaker feeds, but a something that can be 'decoded' into<br>
speaker signals. In its simplest form you could compare<br>
it to representing colour video not as RGB, but as<br>
(intensity, colour, saturation) which can be decoded<br>
to RGB, or to any other colour representation.<br>
<br>
On a first mathematical level, you can see this as a sort<br>
of 'spectral' representation. Any cyclic function can be<br>
Fourier transformed into a set of harmonic frequencies,<br>
each having its level and phase. In similar way, the<br>
horizontal distribution of sound directions is a cyclic<br>
function, not of time but of the horizontal angle (azimuth)<br>
of the sources, and you can apply the same Fourier transform<br>
to it, which is how horizontal AMB works. The 'order' of an<br>
AMB system refers to how many 'harmonics' are used.<br>
For a periphonic (3D) sound distribution the 'function on<br>
a circle' becomes a 'function on the sphere', depending on<br>
two variables, azimuth and elevation. Because a sphere is<br>
not the same as a 2D hyperplane the corresponding spectral<br>
transform is not the 2D FT, but is defined by the set of<br>
'spherical harmonics'. And here of course the more difficult<br>
maths start...<br>
<div class="Ih2E3d"><br>
<br>
> I've read back through your comments about<br>
> routing to A and B to achieve 'local' and overall<br>
> placement, re convolution, but i will admit i don;t<br>
> understand all of it.<br>
<br>
<br>
</div>I'll comment on this later.<br>
<div><div></div><div class="Wj3C7c"><br>
Ciao,<br>
<br>
--<br>
FA<br>
<br>
Laboratorio di Acustica ed Elettroacustica<br>
Parma, Italia<br>
<br>
O tu, che porte, correndo si ?<br>
E guerra e morte !<br>
</div></div></blockquote></div><br>