Running Kubuntu (KDE) 20.04
TLDR: Pusleaudio won't pass AC3/DTS to my external DAC via coaxial S/PDIF, but ALSA will if an application has a setting to direct output to ALSA.
I'm using my motherboard's coaxial SPDIF connection to connect to my 5.1 speaker system that has it's own DAC (Logitech Z906). The only way I've been able to get 5.1 surround to work is with VLC audio set to ALSA audio output > S/PDIF when available, 5.1 Surround Output. So I know the hardware works if I can go directly to ALSA taking Pulseaudio out of the picture. Unfortunately, very few applications, and no web browsers offer a setting (that I can find) to force output directly to ALSA. I've been researching how to get Pulseaudio to pass AC3/DTS directly to my sound system but just can't seem to make it work. So watching movies with AC3 5.1 in a web browser (Plex, Netflix, etc), all get down mixed by Pulseaudio to two channel PCM.
I've tried the steps posted on the Help Ubuntu: DigitalAC-3Pulseaudio and that didn't help. I've also seen several references to change the default speaker channels in /etc/pulse/daemon.conf/ to default-sample-channels=6, didn't work either.
Additionally, I tried to set the card profile per Problem with 5.1 AC-3 through Alsa to pacmd set-card-profile 0 output:iec958-ac3-surround-51 and I get the error "No such profile: output:iec958-ac3-surround-51". (Probably not surprising since this answer was for Ubuntu 14.04)
pavucontrol: (same settings show up in Pulseaudio Volume Control GUI)
Configuration tab: the only options for digital output are "Digtial Stereo (IEC958) Output" and "Digtial Stereo (IEC958) Output+Analog Stereo Input". Several websites said this is correct as Pusleaudio "should" pass AC3/DTS directly to the external DAC via S/PDIF. I have selected "Digtial Stereo (IEC958) Output".
Output Devices tab: I've selected Port "Digital Output (S/PDIF)" and under "Advanced" I have DTS, AC3, MPEG, and AAC selected.
AlsaMixer:
By default after boot it always comes up with PCM on, and Front Speakers On. Every other channel is muted. I unmute Surround, and LFE and make the volume sliders full. This doesn't seem to help either. AlsaMixer appears to be set to the correct sound device Card: HDA ATI SB, Chip Realteck ALC892. If I select F6 to "select sound card" 3 items are listed, HDA ATI SB (the one I'm using), my webcam, and my NVDIA graphics hard (HDMI). So it appears the correct sound card is selected.
I looked into getting rid of Pulseaudio all together and just use ALSA... but it seems like Pulseaudio is heavily integrated and would cause a lot of issues if removed (the dependency list is huge, including KDE, try to remove it (sudo apt remove) and it will take down KDE all together leaving me with a command line only system.
Any suggestions?
Thanks!
