[openal] Speaker test

Chris Robinson chris.kcat at gmail.com
Mon Jun 5 11:36:45 EDT 2017

On 06/04/2017 09:43 PM, Anders Genell wrote:
> Oh?! Fantastic! Is it documented somewhere how to implement this?
> Looking at e.g. Fons Adriaensen's ambisonics decoder for linux, it
> seems angles should be possible too.
> http://kokkinizita.linuxaudio.org/linuxaudio/adec-pict.html

What exactly do you mean by angular correction? The speaker itself being 
turned to a different angle (e.g. it facing away from you instead of 
toward you), or that it's placed at a different angle relative to your 
front (e.g. front-right is 40 degrees to your right, instead 30 
degrees)? The latter is possible by generating new decoder matrices for 
your specific layout, using something like the Ambisonic Decoder Toolbox 
(a set of MATLAB/GNU Octave scripts to generate ambisonic decoders). 
OpenAL Soft doesn't currently have a way to generate the decoders 
itself, since the math behind doing so isn't very straight forward, but 
I do plan on doing it eventually.

For setting the time/phase correction, the first step would be to look 
at the ambdec presets provided in the presets/ directory and find the 
one that's most appropriate for your speaker setup (keeping in mind that 
7.1 should use "hexagon"). Make a copy of that file and edit it. In the 
"speakers" section of the file, you'll see speaker IDs and their 
distances. Set the the correct distances (in meters) for each speaker 
and save. Then run alsoft-config, and under the Renderer tab you'll see 
the Decoder Configuration section; click Browse and select the new 
preset you made for the correct speaker layout, and click Apply. It's 
now set. You can also enable High Quality Mode while you're there if you 
wish to use frequency-dependent processing.

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