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I have Ubuntu 14.04 installed (i386 Architecture) on Zotac ZBOX-ID18.

I am trying to output digital surround audio through digital SPDIF output, I understand that the default SPDIF output is on PCM format which is stereo only (not 5.1 surround).

I did install the AC3 plugin using the below as a reference, however even after selecting "Digital 5.1 Output" profile, I don't get any audio output at all.

https://help.ubuntu.com/community/DigitalAC-3Pulseaudio

I tried forcing this profile from default.pa and from pavucontrol but still no luck :(

Also tried running aplay -D a52:0 but not getting any output.

In some random cases I was able to output digital surround by playing test videos but it happened only few cases and couldn't relate this cases with any other events or config changes, it was pure random.

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  • I have the same problem, if you use VLC to play, all you have to do is changing the audio output module from default to Pulseaudio.
    – user326252
    Sep 12, 2014 at 17:07

5 Answers 5

Reset to default
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Finally managed to set this permanently, I had to add the following command in the startup applications.

pacmd set-card-profile 0 output:iec958-ac3-surround-51

To verify the name of you sound profile, run following command, u'll get all available profiled for ur sound card.

pacmd info

For some reason adding this default device in default.pa didn't work, but adding it as a startup command is working, now I don't need to open pavucontrol every time I reboot my machine.

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  • You might want to also try the solution I've just posted too, if you still have the same setup and if you think it might also be PulseAudio auto-switching to other connected devices by itself all this time!
    – Julie Brandon
    May 16, 2020 at 2:15
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Same issue as John N, trying to get SPDIF working on a Zotac box, using Ubuntu 14.10. I walked through the same steps, and got 5.1 channel sound selected, but when trying to play videos without pavucontrol open the videos would freeze and the AV receiver would show intermittent signal being received. Leaving pavucontrol open did indeed enable playback of any video, through mplayer, VLC, or XBMC.

Trying the pacmd command in startup applications, however, did not solve the problem. Neither the example given nor any relevant variation worked, and I'd welcome input on configuring that command.

Ultimately what I did was simply add pavucontrol to the startup applications and leave it running in the background or minimised while using XBMC or other playback utilities. Not elegant, but effective, especially since no future user can accidentally forget to run pavucontrol before trying to play a file.

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  • If you're still using your Zotac box (I am) you might like to see my alternative solution, cos I bet it's the same issue! In /etc/pulse/default.pa comment out "load-module module-switch-on-port-available" and "load-module module-switch-on-connect" -- it's been PulseAudio auto-switching to other connected devices by itself all this time!
    – Julie Brandon
    May 16, 2020 at 2:13
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This wasn't working for me in Ubuntu 20.04.1 (Focal Fossa) until I configured /etc/pulse/daemon.conf and changed

; default-sample-rate = 44100

to

 default-sample-rate = 48000

Don't forget this step! :)

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I eventually had luck by doing the weirdest thing. Leaving pavucontrol up. That's right - I just don't close it. As long as I select one of the two Digital Surround 5.1 profile options (one includes Analog input) under the built-in audio section under the configuration tab of pavucontrol then DON'T CLOSE that app, I get working 5.1 audio in all other programs. If I close it, I go back to wonky issues including my receiver freaking out trying to decode whatever my computer is outputting and not knowing what to do.

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  • Just tried it and it worked! Thanks a lot, this explains why in some cases it used to work, probably I had pavucontrol left open.
    – John N
    Jun 18, 2014 at 14:07
  • Sadly this is no longer working for me on 16.04
    – tamale
    Jan 11, 2017 at 4:38
  • Yep, leaving pavucontrol open stopped working for me too. :( I'm now up to 18.04 and was determined to get to the root cause of it and did. By default PulseAudio auto-detects and auto-swaps devices by itself, including to things like HDMI Audio if you happen to be using an HDMI detected TV. See my other solution post for how to disable it!
    – Julie Brandon
    May 16, 2020 at 2:18
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I too have been battling with the issue of the software encoded AC3 SPDIF output getting disabled and having to use pavucontrol to set it back since 14.04 (I'm on 18.04 and had the same issues until now.)

Your issues may be PulseAudio auto-detecting attached devices and changing to them (in my case, auto detecting and then changing to the HDMI audio output.) If you think this might be causing these issues then in 

/etc/pulse/default.pa

comment out

#load-module module-switch-on-port-available

and

#load-module module-switch-on-connect

I'm so very glad to finally be able to nail this annoying issue properly on the head!

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