Thanks Florian, will have a look at this although I'm really aiming to decode outside of SC.
I sent my original message to Fons. He replied with the following and given what he said, I'll likely use FMHEncode0 (which I was unaware of) along with ambdec:
FMHEncode0 seems to produce correct FuMa scaled levels.
FMHEncode1,2 try to do something with distance. As far as
I can see, the way the 'rho' paramter is used does NOT
produce correct encoding for rho = 1, and the wComp
thing seems to be an attempt to correct for this. You
could check this by comparing the output with that of
FMHEncode0.
It is possible to create some 'internal' effect by
reducing the non-zero order components and that is
probably what this 'rho' thing is supposed to do.
But it doesn't look correct to me. And anything
beyond the radius of the speakers is nonsense, it
just produces completely incorrect decoding and
completely destroys any advantages that higher
order could offer.
Distance perception is better controlled by reverb
and early reflection levels.
Anyway whatever those two ugens seem to do is meant
for a decoder expecting FuMa scaling. So yes, you
could use Ambdec.
Em 20-12-2015 23:55, fgrond escreveu:
Hello Iain,
I have no experienece with Fons Adriaensens ambdec, but I recently explored the ambisonics decoder toolbox by Aaron Heller:
https://bitbucket.org/ambidecodertoolbox/adt.git
It is a Matlab / Octave toolkit which allows you to generate decoders of various orders and flavours (FUMA, ambix, ...).
The outputfiels are either for ambdec, the ambix suite or as Faust .dsp files, which you can then compile amongst others as SuperCollider Ugens, so you can do the decoding directly in SuperCollider.
Cheers,
Florian
On 20/12/15 14:23, Iain Mott wrote:
Hello list,
Is it possible to use Fons Adriaensen's ambdec to decode FMHEncode1/2 encoded 2nd order signals? If so, which of FMHEncode's two scaling modes correspond to one (or two) of the 'N3D', 'SN3D' and Furse-Malham scalings available in ambdec?
I'll paste below the paragraph on scaling in the ambdec manual
Thanks,
Iain
In order to correctly use some of the options discussed below, the following must be understood.
Ambisonic signals are traditionally scaled in a number of di erent ways.
For mathematical analysis it is very convenient to use the normalised form, meaning that each
spherical harmonic has unity power when integrated over the sphere. This is called the 'N3D'
form of Ambisonic signals. A close variation on this is the 'semi-normalised' or 'SN3D' form. This also has desirable
mathematical properties, and is used by some existing software, for example the Ambisonic
tools from IEM, Graz. The alternative to both, and widely used, is the so-called Furse-Malham form. This applies some gain factors to the signals so that they all have the same maximum level over all directions. The
only exception is the pressure signal W which, for historical reasons, is attenuated by 3 dB.
Many Ambisonic applications and audio les use the Furse-Malham representation.
AmbDec allows to use all three representations, both for the input signals and for the matrix
coe cients. If the two settings are di erent, AmbDec will automatically apply the necessary
gain factors to convert between them. So you can design a decoder matrix using the normalised
form (which is usually less confusing, in particular for higher orders), and then use it with signals
scaled according to the Furse-Malham standard. Important note: the normalised form used is always the 3-D one, even for an horizontal-only decoder. The reason for this is that all decoders are used in 3-D space | unless your speaker are in nite vertical line sources the rules of physical 3-D space apply, even when analysing a 2-D
decoder.
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