Sonos Arc changes audio formats after switching off TV.

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!

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.

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.

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. 

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.

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.

Hi @GCGQLD 

Yes - the result should be the same.

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. 

Hi @GCGQLD 

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.

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.