[LAU] Ambisonics for newbies - ambdec

[Michael Jarosch]

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