Re: [LAU] Jconv

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. :)

Alex.

On Sun, Jan 11, 2009 at 3:57 PM, Fons Adriaensen <fons@email-addr-hiddenwrote:

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 often contradictory, frequently outdated, and in some cases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

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Received on Sun Jan 11 16:15:02 2009