[LAD] ambisonics UHJ encoder

fons at kokkinizita.net fons at kokkinizita.net
Tue Feb 23 18:18:17 UTC 2010

On Tue, Feb 23, 2010 at 04:37:53PM +0300, alex stone wrote:

> Jorn, Fons, i'm looking for a ladspa UHJ encoder, and can't seem to
> find one. Any idea if such a beast exists? Or if there's a standalone
> instance or ambdec preset i can use, and route in and out of?

Jconvolver can do this, there's a config file 
in the distribution.

> Some general questions.
> When i use Jconvolver standalone (my preference) and test with a
> *amb.conf, i get 1 input and 4 outputs WXYZ. Is this correct for 4
> signals coming into 1, into the *amb.conf, or do i need to change this
> to reflect individual WXYZ routing, from something like a MASTER
> strip, or from an ambdec plugin in a channel strip? (i'm trying to get
> the signal chain sorted out correctly.) i.e. 4 in, 4 out.
> I'm using all mono ins for sound sources, and want to reflect
> positioning in the busses, as i have multitrack 1st violins,
> 2ndviolins, etc...
> So my 1st violins (4 monotracks) are going into a 1stviolin buss (4
> ins) and in the buss signal chain, i'm adding a ladspa amb mono
> panner, which naturally gives me 4 outs, then the chain continues to
> the MASTER and jconvolver, back into a jconv buss in the mixer with
> the intent of finally routing that to the UHJ buss...

This is not the recommended way to use such a reverb.

The outputs from jconvolver should just go into the
AMB mix bus. If you use Ardour you can connect them
directly to the master bus, or you could use a 'bus'
strip to have a gain control at that point.

The input of jconvolver should normally come from 
post-fader aux sends on the same strips as where
you insert the AMB panners - the panner and the 
aux send get the same post-fader signal.

This way you can set the level of reverb for each
panned source separately. The relative level of
the reverb is also preserved when you use either
the channel or master faders, as the reverb sits
in between those, as a side chain of the master

In fact you can do this becaus a convolution 
reverb is a linear process: reverb (a) + reverb (b)
= reverb (a + b). 

To be used like this the reverb must *not* include
the direct sound.

Ideally the input to the panner should also have
a variable delay - to put a source at a larger
distance you would then increase the send to the
reverb and increase the delay in the direct sound
via the panner. But this is a refinement that is
difficult to arrange in Ardour, it requires using
two strips for each panned source. 

If the reverb has many inputs corresponding to
different source positions you would have as
many aux busses, plus one extra for the 'tail'
of the reverb which is usually a separate input
for jconvolver.



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