On 5/31/19 10:25 AM, Sean Devonport wrote:
Hey everyone! Hope all are doing well.
...
So far, I've managed to get a decent spatial impression, however, I've been
running to this issue where the top speakers seem to emitting too high
volumes. I've tested against the SPARTA
<http://research.spa.aalto.fi/projects/sparta_vsts/> decoding plugins and
have also been experiencing similar problems. My thoughts are that the
AllRAD approach in the IEM <https://plugins.iem.at/> plugins would be
similar.
[MUNCH]
*Attempts at solutions:*
Some things I've done to try eradicate the problem is to feed 'vertically
spreaded' loudspeaker elevation angles to the algorithm to try increase
vertical separation. Or to offset my centre of origin so the angles to my
loudspeakers are solved according to different levels of elevation within
the centre of my loudspeaker arrangement. This has helped somewhat, but I'm
not 100% happy with it as of yet.
The other thought I've had would be to perform better speaker tuning, so to
compensate for any sound propagation delays and attenuation because of
location although based on this paper
<https://iaem.at/Members/frank/files/2014_frank_howtomakeambisonicssoundgood.pdf>,
this may not be the correct approach.
You do not say, but I presume the top speakers are closer than the side
ones? (at least that is the case in all the arrays I have done decoders
for - I calculate them using ADT).
If that is the case and you have not compensated for that - ignore the
rest if you already did that, I would suggest you first delay the top
speakers the right amount so that all signals arrive at the same time at
the center of the space (otherwise the precedence effect will tend to
localize things to the closest one). You will also need to attenuate the
signal to the closest speakers so that they are all sounding with the
same SPL given the same input signal.
In my experience it is only then that you can start testing decoders...
I also equalize them (measure impulse response, then design inverse
filters with DRC), and get much better results after that (and don't
forget to redo the level eq after that, it changes...). It is not only
the speakers are flatter, but they also sound much more similar to each
other and that also helps.
-- Fernando
PS: I have also had a problem with, after all these things been taken
care of, a 3d panned pink noise signal would not be equally loud in all
directions. What I mean is, individual speakers would have the same SPL,
same noise sent through the decoder and panned to the speaker locations
would not (louder towards closer speakers).
To tell the truth I should redo all measurements as there might be
something wrong, not the first time I would make some basic mistake. I
ended up implementing an ad-hoc level compensation curve based on the
measurements that would deal with this, and the result is much more
balanced.
I do not have an explanation as to why this was happening...
(this is on our Stage, a small concert hall - seats about 45 for full 3D
immersive sound, up to 80 for regular concerts - with a 56.8 system. The
space is challenging, very rectangular, low ceiling compared to the
dimensions and trusses everywhere :-)
https://lac.linuxaudio.org/2019/doc/lopez.pdf
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