I wanted to continue to chronicle some of the little tweaks and fixes I've made to my system as I go, and this is the latest one.
In a nutshell, it seemed that no matter what settings I changed in sound properties or computer settings that any stereo content (no matter the source) was upmixed/unwrapped from stereo to a kind of 'horseshoe' soundfield that pushed sounds from the far left and right of the stereo image to the back speakers. I'm a simple guy - I want my chocolate milk cold, my women fast, and my stereo music only coming out of two speakers.
This was something that had been bugging me since I first set up my system a year ago, but I kind of ignored it because Kodi 17 seemed to bypass this behaviour somehow, and when I was streaming stuff (Netflix etc.) from a web browser I would just force my AVR in to stereo only mode.
However, things finally came to a head when I installed Kodi 18 and the same 'stereo upmix/unwrap' behaviour that was previously bypassed in v17 was being applied to stereo material played back in Kodi.
It turns out that this isn't a 'bug', but a 'feature' of Pulseaudio, the standard audio driver for (some? most? all?) Linux variants, and it's pretty simple to remedy. To disable it, take the following steps:
Open a terminal window, and type the following command:
sudo gedit /etc/pulse/daemon.conf
This will open the configuration file for the audio driver in a graphical text editor. Next, scroll down (in mine it was about 1/3 of the way through the file) until you find the following line:
; enable-remixing = yes
and change it to:
enable-remixing = no
And save the file - the 'save' button is at the top right of the gedit window. It's important to note here that you're not just changing 'yes' to 'no' here - you have to remove that semi-colon before the line to make the change "active"...something that took me about an hour of fiddling around to figure out.
Once you've done that, reboot your machine, and voila, no more weird 'horseshoe' upmixing. I found this especially beneficial because now if I'm listening to stereo content and I want a pseudo-surround experience I can use my AVR's functions like Dolby Pro-Logic etc.
One final note - my AVR only has 5.1 outputs, but in the Mint sound configuration panel after I selected HDMI as my output device I could select anything from 2.0 up to 7.1 channels of output. Initially, I chose 5.1 (to match my speakers) but after that I noticed when I was listening to some quad material that should've been super-discrete (ie no front/rear bleed) that the front and rear channels sounded somewhat "blended" - I changed my output channels to 7.1 after that and the problem disappeared, all the channels are 100% discrete.
I'm guessing that even though my AVR only has 5.1 speaker outputs, that it must be able to accept (and downmix) 7.1 signals via HDMI, and that's what it was reporting to the output device (ie my NUC). So my advice to anyone setting one of these up that you pick whatever the maximum number of channels available is, no matter what you think your AVR is capable of - if it doesn't work then just step down in increments until it does.