[LAU] Ambisonics for newbies - ambdec

Fons Adriaensen fons at linuxaudio.org
Wed Mar 25 12:15:22 CET 2020

On Tue, Mar 24, 2020 at 05:27:16PM +0100, Michael Jarosch wrote:
> Am 24.03.20 um 08:04 schrieb Jeanette C.:
> > Mar 24 2020, Mitsch has written:
> >
> > Yes, first oder ambisonics also has four channels, known as W, X, Y and
> > Z. But these don't mark speakers, they mark pressure (overall loudness)
> > and three directions.
> It took a while, but I understand the basic mechanics of ambisonics, now
> - at least, I hope so.
> It's a bit sad, that there seems to be no "ambisonics for newbies" site
> to make it a bit easier to dive into this… The "Using ambisonics with
> Ardour"-page really helped a lot, although the plugins and input
> descriptions do not match to what I was confronted with.
> > And so what ambdec does is decode one of the ambisonic formats into a
> > particular speaker setup.
> That's right - I just have to use a configuration in ambdec that matched
> my speaker setup. I expected a configuration called "quadrophonic", but
> I found a "square". Maybe quadrophonic is already occupied by another
> surround systems nomenclature… Well, I'm fine with a "square"…
> I would have made my own configuration, but I couldn't find the button
> "new" in the configuration dialog, which was described in the manual of
> the 0.4.2 version I've found on Fons' page. Is that handy tool given up
> in later versions or am I too dump to handle it right?
> >> Following instructions from https://community.ardour.org/ambisonics,
> >> I added one mono track, bypassed the builtin panners and took (I
> >> think it was) "AMB 1.1 mono panner" (couldn't find "1h1v"), added 2
> >> additional channels in "Master" to get 4 of them and let my mono
> >> channel take the "Master" as an output.
> > Again for clarity: there is a LADSPA plugin - also by Fons - called "AMB
> > order 1,1 mono panner", which will do and is probably what you have
> > used?
> Yes! That's the right name.
> >> Then I started ambdec and tried to make some sane connections, but
> >> the inputs are not called "w", "x" and "y", but only "0", "1", "2",
> >> and so on?
> > As far as I can see, that's OK. Connect your four outputs to the first
> > four inputs of ambdec.
> Yeah, I've tried that. Master 1,2,3,4 to ambdec 0,1,2,3 via "catia".
> By the way, @Fons, if he is watching that thread: I can't understand,
> why counting in an audio application starts at "0". And I can't
> understand why it seems better not keeping the ambisonics' nomenclature
> for an ambisonics application… There may be reasons for this - maybe 3rd
> order ambisonics complicates things, here? Nevertheless: Is it possible
> to name the inputs at least by a number AND the corresponding ambisonics
> channel name? That would be great!
> I made sure, that the outputs of ambdec are correctly connected, which
> is easy to test with the internal test signal. But there are a few
> things that let me think, I'm wrong with the inputs, here:
> * If the "mono panner" is in a neutral position (Azimuth: 0, Elevation:
> 0), I would expect to get a signal from exactly in front of me. Instead
> I get an output signal of LF and LB which is 20dB higher than RF and RB.
> I can reach the signals position that corresponds to the one I expected
> if I set Elevation to 90. But then, changing azimuth does nothing
> (instead of  - my expectation - circling around me while changing it).
> * Elevation: The Ardour page says, if there's no vertical dimension, I
> shouldn't connect "z" - if I do that, ambdec changes it's reaction to
> the "mono panners" values - but still it's not very intuitive to work
> with. Or to be more precise: It's even getting worse…
> Conclusion: I'm sure, ambisonics is no rocket science, but the tools I'm
> depending on getting ambisonics to work don't make it that easy…
> Greets!
> Mitsch
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