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Sonos Arc changes audio formats after switching off TV.

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I have had this problem since I purchased the Sonos Arc about a month ago and it is getting very frustrating.

I have a TCL 75C727 TV with the Sonos Arc connected in the eArc HDMI port and stream everything through an Nvidia Shield TV Pro. The TV is set to passthrough audio.

When I first start up everything the Sonos Arc is outputting the correct audio formats.

For Disney+ the app will show Dolby Atmos and Dolby Digital Plus 5.1 correctly depending on media.

For Netflix it is Dolby Digital Plus 5.1 and for Youtube it is Stereo PCM.

However once I turn off the Nvidia Shield and TV and turn everything on in a few minutes the only format that works correctly is the Dolby Atmos. All the other formats show up as either Dolby Multichannel PCM 5.1 or Dolby Multichannel PCM 2.0.

I have tried powering down the TV and the Shield but the problem only resolves when I power down the Sonos Arc and restart it and then the audio formats are correct again, until the next time I want to watch something.

Has anyone else had this issue with their setup and how did you resolve it. 

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Best answer by GCGQLD 2 September 2022, 03:36

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21 replies

Corry P
Userlevel 7
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Hi @GCGQLD 

Welcome to the Sonos Community!

I too have a nVidia Shield and noticed that, with my TV supporting DD+ but my Amp not doing so, the Shield would still output in DD+ if I left the Shield’s audio output format setting on Auto. I think this has more to do with my TV than with the Shield (or the Amp), but manually selecting the supported formats in the Shield’s settings (tick Atmos, Dolby Digital + (aka E-AC3), Dolby Digital (aka AC3), DTS and PCM) rather than leaving it on Auto may help.

I wouldn’t be concerned about seeing 2.0 Dolby from YouTube - I see that all the time. It makes no difference.

It’s also possible that your Shield apps are “arguing” with the Android settings as to which format to use - you may need to alter the apps’ settings too. It sounds like an app, Android, or the TV is deciding to transcode to Dolby Multichannel PCM 5.1 before the stream reaches the Arc. Rebooting the Arc would force the TV to re-evaluate which codecs are acceptable (via HDMI-CEC), which I believe is why only rebooting the Arc seems to resolve it.

If you’re not rebooting your TV by unplugging it from power for a full minute, I’d try that too.

Do you have any other devices connected to your TV via HDMI? If so, I recommend testing with those devices disconnected - if the issue then goes away, look to disable CEC features on the disconnected device(s).

Lastly, you may also want to check for a “Bitstream” option on your TV’s format setting and try that.

I hope this helps, though I also hope someone with both a Shield and an Arc jumps in!

 

"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein
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Thanks for the reply Cory P. 

I had a similar setup that I have now with an Amp before I changed to the Sonos Arc and never had this issue. The main difference was that the amp turned off when I switched off the TV and Shield. Which makes me think that what you mentioned about the TV re-evaluating the codecs when the amp came back on is why it worked. If this is the case is there a way of shutting down the Sonos Arc when I switch off the other devices. I could not find anything in the S2 app.

I do not have any other device connected to the TV, just the Shield. 

I could not find a “Bitstream” option on the TCL but was reading that is what Passthrough is.

Thanks again for the info.

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Just an update on my dilemma.

I have removed the Nvidia Shield and tried with the built in Android TV on the TCL.

Had the same issue. Would start Netflix in Dolby Digital Plus 5.1 but after switching off for a few minutes and trying again it would revert to Dolby Multichannel PCM 5.1 until I turned off the Sonos Arc.

I disconnected everything from the TV and started over by resetting the TV and then plugging in the Sonos Arc and connecting the TV again via the app. Same problem after switching off TV.

The only good thing from this is that it is not the Shield causing the issue. It is either the TV or the Sonos Arc.

I am going to trying turning off the “Quick Start” option on the TV and see if that makes a difference. I will update once I have tested.

106rallye
Userlevel 7
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As I understand it the Arc just tells the TV what formats it can play. The TV then decides what to send it. My bet is on your TV not getting HDMI-CEC right. 

Corry P
Userlevel 7
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Hi @GCGQLD 

I confess I’ve never understood why TVs have both Bitstream and Passthrough - to me, they’re the same thing.

I would now also have to put this down to the TV - the Arc will only ever report the format it receives, so it does seem that the TV is the only possible culprit left.

Bear in mind that 5.1 PCM is what any surround sound input format will get converted to (apart from Atmos) - PCM is what digital audio devices use internally, and everything else is just compression technique. If you still actually get 5.1 audio, there isn’t really any harm in it.

If, however, when playing Dolby Digital Plus, the source is 5.1.2 (compressed Atmos) and you get 5.1 delivered to the Arc setup, that’s an issue.

"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein
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Thanks for all the info. I will try a few more things over the weekend.

Just a question about the TV. If powering down the Sonos Arc fixes the issue should powering down the TV and leaving the Sonos Arc on do the same. I assume they will renegotiate the codecs in this case.

Corry P
Userlevel 7
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Hi @GCGQLD 

If powering down the Sonos Arc fixes the issue should powering down the TV and leaving the Sonos Arc on do the same. I assume they will renegotiate the codecs in this case.

Yes - the result should be the same.

"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein
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I tried just powering down the TV and restarting but this made no difference. The audio was still not correct until I powered down the Sonos Arc. Not sure what this proves though. 

Corry P
Userlevel 7
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Hi @GCGQLD 

I tried just powering down the TV and restarting but this made no difference. The audio was still not correct until I powered down the Sonos Arc. Not sure what this proves though. 

Neither am I, to be honest.

Though it sounds like the only issue is what the app reports - if you get Atmos when you should get Atmos, 5.1 when you should get 5.1 and stereo when the source is stereo, I would just say ignore what the app says. It’s the audio output that’s important.

"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein
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I’m pretty sure the app has it correct as I do notice a big difference in the sound quality between Dolby Digital Plus 5.1 and Dolby Multichannel PCM 5.1. The Dolby Digital sounds much better, but I have to restart the Sonos Arc to get it.

If anyone has any ideas on what my next steps should be I would love to hear it.

I don’t want to get rid of the Sonos Arc as it sounds great when it is working correctly.

 

Corry P
Userlevel 7
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Hi @GCGQLD 

Could you please submit a support diagnostic once while the app reports DD+, and again when the app reports Multichannel PCM 5.1, then reply here with both of the numbers given? Thanks.

"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein
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Thanks for all your help on this  @Corry P 

The first diagnostic number is 1075590124 and this is for the Multichannel PCM 5.1.

I then powered down the Sonos Arc and it restarted with DD+ and diagnostic number is 1492710998.

Both diagnostics done watching Netflix.

Cheers.

 

 

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Every now and again I get no sound at all. I have a diagnostic number 509832812 for that just in case it helps.

Corry P
Userlevel 7
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Hi @GCGQLD 

Thanks for the diagnostics.

The first shows MAT Atmos being played, but ARC is reported as being in the “incorrect mode”. 5.1.0 sound was reported, which doesn’t need MAT so perhaps this makes sense. eARC was online.

The second shows Dolby Digital +, also 5.1.0. ARC is reported as normal. 5.1.0 audio again. eARC was reported as disabled - presumably because DD+ doesn’t need eARC to work.

The third shows PCM, 2.0, and also reports ARC as being in the incorrect mode. eARC was online again. It does not indicate that nothing is being played.

Seeing as eARC seems to be flipping with the audio codec, please try disabling eARC in the TV’s settings. This will prevent you from receiving MAT (uncompressed) Atmos, but compressed Atmos via DD+ should still work.

Was your Netflix app reporting Atmos for the media you were testing with? I ask because in none of the diagnostics was the Arc reporting 5.1.2 audio.

 

Edit: So I had a chat with a senior colleague and the “Incorrect mode” doesn’t refer to the codec used but to the fact that the Arc/TV handshake didn’t go well. Once an audio device connects to the the TV, the TV has to disable it’s own speakers, pipe the audio through the ARC channel, divert volume commands via HDMI-CEC and the audio device will report its current volume level so the TV can display it. This is collectively referred to as SAM (System Audio Mode) and does not seem to be going well.

I highly recommend you check your TV for available software updates, but if possible, I recommend testing the Arc with another TV - though I appreciate that even if you have a spare TV it’s unlikely to also have eARC, this being a newer feature. Please also double check the HDMI connections, and use the cable supplied with the Arc if you aren’t already. Swapping the ends of the HDMI cable round may help if there is a less-than-perfect electrical connection in the sockets with the current configuration.

I hope this helps.

 

"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein
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Thanks Cory P. I am away at the moment but once I get back will try the cable change etc. Don't have another eARC TV to try but I will try disabling eARC as well and see how that goes. I’ll post my findings after.

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Hi Cory,

Finally tried a few things but still having some issues. I could not use the original HSMI cable that came with the Sonos as it was too short, but I did try with a certified 2.1 HDMI cable and made no difference.

I then tried disabling eArc. This again did not fix the problem I have some diagnostics if you would like to take a look. 2110828924 everything was showing as 2.1. After restart 267476021 for 5.1 DD+ and 2114483073 for Atmos.

Don’t have access to another eArc TV but a mate of mine is getting one seoon and I will take it over and try.

Cheers.

Corry P
Userlevel 7
Badge +18

Hi @GCGQLD 

OK, that final diagnostic was the first time I’ve seen 5.1.2 being reported - so it’s good that you can, at least, get proper Atmos sound. I see that you had to reboot again to get that, however, looking at the uptime.

From that point, if you were to switch to another movie, would you then get 2.0 again until you rebooted the Arc once more? As in, will you only get 5.1.2 if you reboot the Arc after the movie has started?

I’m not sure what I’d do with the answers to these questions, but if they’re Yes, then I guess it re-enforces the idea that the TV is at fault.

I presume the cable was to short because your TV is wall-mounted? The amount of times I’ve seen people on this forum struggle with TV audio issues until they go back to the supplied cable is surprising - if you can arrange things so you can use the supplied cable at least temporarily for a test, that would presumably be easier than lugging your Arc round to your friend's house. Admittedly, it seems like a long shot, but if it’s not too difficult, worth trying.

I hope this helps.

"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein
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Hi Cory P,

Once I have restarted the Arc all movies play correctly in all apps. I can go back to Atmos and it is all good after watching 2.1 or 5.1. It is only after switching TV off for a bit and turn back on were everything reverts back to 2.1.

I will arrange things so I can try the supplied  cable and let you know how that goes.

Thank again for all your help.

Cheers,

G

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Something interesting just happened. My daughter turned on the TV after being off all night and watched Netflix in 5.1 and the Arc is correctly playing DD+.

Now I need to work out which app maybe changing the Arc to 2.1 and then does not change back.

I’ll get back when I have more information.

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It seems to be working 95% of the time now. I have switched of eArc on the TV and most of the time when it comes on the sound on the Sonos Arc is playing correctly, so I am pretty happy with the outcome.

The Dolby Atmos is also playing from Disney+ as I assume it is compressed and does not require eARC as Cory P mentioned above.

Every now and again it reverts back to Stereo but then the next time is will be OK. No idea why but I can live with that.

Thanks again for everyone’s help.

 

 

Corry P
Userlevel 7
Badge +18

Hi @GCGQLD 

I’m glad to hear that things are at least satisfactory, if not ideal. You are correct - streaming services will supply compressed Atmos via Dolby Digital +, which can be carried over standard HDMI-ARC. Only exterior devices are ever likely to supply an uncompressed format, and they can often be told to send compressed streams instead.

Thanks for updating the thread.

"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein
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