On 03/22/2016 07:49 PM, Martin Dupras wrote:
Today I tried playback sources in third order Ambisonics on a 8+6+1
hemispheric speaker array using Reaper. It didn't quite work as
intended so I'm trying to figure out where I've gone wrong.
I was using the Blue Ripple TOA-Core panner plugin to position the
sound. I understand that Blue Rippler plugins use the Furse-Malham
convention.
The only decoders that I could find to decode to my specific array
(using coefficients that I calculated using the Ambisonics Decoder
Toolkit) were the Ambix Plug-ins and AmbDec.
I tried Ambix first, which I understand uses the ACN ordering
convention. I tried re-ordering the channels based on information that
I found here: https://en.wikipedia.org/wiki/Ambisonic_data_exchange_formats#ACN.
But that didn't really work.
I then tried to run 16 outputs out of Reaper into Jack, and from Jack
into AmbDec, again using my ADT-calculated coefficients. I understand
that AmbDec uses the Furse-Malham convention, so I would have thought
it was compatible with the output of the Blue Rippler plugins. But
again, that didn't really work well at all.
In both cases the sound was coming from seemingly random places, and a
number of positions went practically silent.
To debug erratic panning behaviour, start with first order, verify, and
work your way up from there. To make sure the error is not in your
calculated coefficients, try to use a known-good decoding matrix that
approximates what you have, before feeding in your optimized one.
With Ambdec, weird things can happen if you connect several ins at the
same time using some graphical client, because the order shown in for
example qjackctl is lexical, whereas the internal order is different. So
you will end up with garbled connections. You can feed an ACN signal
into ambdec succesfully if you choose SN3D input scaling _and_ manually
connect the inputs correctly.
This wikipedia article
https://en.wikipedia.org/wiki/Ambisonic_data_exchange_formats
has some information on that, and other pitfalls when interfacing
different formats.
All best,
Jörn
--
Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister für Veranstaltungstechnik (Bühne/Studio)
Tonmeister VDT
http://stackingdwarves.net
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