Please read if you have encountered issues with 7.1 LPCM playback on Sonos via an LG TV

Hi

Is there any particular content/ test pattern we could use to test this issue, as I presume its not easy to hear if there is an issue? 

I have an LG CX and all content over HDMI, be it oppo203, apple tv 4k, all the DD 5.1 audio is ouput as multichannel pcm 7.1, but as you say LG seems to up convert it.

Hi @ledzep1 

That is a good question which I personally can’t really help you with, other than to presume if you were watching an action/sci-fi/superhero movie it would, at some point, be obvious that something was off. Certainly dialogue should be the easiest to spot if not coming mainly from front and centre. If you can find/play a 7.1 test video on a platform/device capable of outputting 7.1 then that would obviously be ideal. If anyone knows of any such tool, please share details here. I have heard that some streaming services have these, but I’m not sure of the details (how many channels and what configuration).

As a few LG CX owners have already reported back stating that they experience no such issues, I’m starting to conclude that it was mis-reported in the first place, or resolved back in July ‘21 when we incorporated 7.1 downmixing to 5.1 into our software

Incidentally, there’s no real harm in the TV converting to LPCM - LPCM is how all digital, audio-capable devices handle audio internally after decompression. Also, the TV only does this when it knows the connected audio device can handle it. Unfortunately, there is often a volume difference, with LPCM being quieter - this is due to the Arc/Beam no longer having an opportunity to boost the gain post-decompression (there is no decompression with LCPM). Personally, I don’t have a Sonos Home Theatre device and I have to adjust the volume on my Samsung BluRay/amplifier with pretty much every program, movie or YouTube video I ever watch, with movies in 7.1 having to be turned up the most (and a lot). It’s just a fact of modern life.

For what it’s worth, I can’t believe there isn’t a setting on LG TVs to prevent them from outputting 7.1 LPCM - my guess would be to not use “Bitstream” as the output format, but my TV is Samsung too, so I can’t test it. Annoyingly, there’s also no way for me to know what codec is actually being played through my audio device - no helpful app!

Whether channels are being mapped to the wrong speakers or not is almost irrelevant. Fundamentally the audio that we are playing from the source e.g. 5.1 is being messed with in the chain somehow and that is the problem - I upgraded to a Beam Gen 2 from a Gen 1 precisely because of the promise of eARC being able to handle full bandwidth audio transferred bit-perfect from the source and that is not happening. It’s possible that the end result is the same (e.g. the TV is adding 2 empty channels which Sonos then drops) but until we get some clarity from Sonos on exactly what is happening and why these questions will continue to be reported here and presumably through your support channels taking up valuable time and effort. Other audio systems e.g. AVRs connected to LG TVs don’t seem to do this as far as I’m aware.

I would assume it would be trivially easy to check some diagnostics and confirm what is happening? Maybe the Sonos end is somehow advertising itself as wanting a 7.1 signal, maybe it is too ambiguous and the TV assumes it’s 7.1 capable? Maybe the app is buggy and reporting 7.1 when in fact 5.1 is being played? Who knows, not the users on this forum certainly.

If the Oppo can play an MKV file, try this DTS-HD Master Audio 7.1 Sound Check:

https://thedigitaltheater.com/tools/

You should be able to AirPlay this 7.1 AAC MP4 file from an iOS device to your Apple TV 4K:

https://www2.iis.fraunhofer.de/AAC/7.1auditionOutLeader_v2_rtb.mp4

Hi @ste_ms 

Not to this thread, which is expressly for the investigation of exactly that, and presumably not to anyone who has to tolerate it. I appreciate that you’re trying to solve a problem that you have, but this thread might not be where to do it.

We don’t “drop” any channels - we downmix them so the channels that don’t have physical speakers to go to end up coming from equivalent speakers (so a side channel would play through the front and back speakers of that side, resulting in still appearing to come from the side). But yes, the end result may well be indistinguishable.

Yes - it is easy. In all cases, diagnostics report that the incoming stream from the TV is 7.1 McLPCM. We have no reason whatsoever to change the format, nor do we. We don’t even include the software libraries required to do so. The app reports 7.1 because that is what is being fed to the Arc or Beam, from the TV. Given that this issue only appears when certain LG TVs are involved, it’s also easy to say that the LG TV is doing it, and that it is doing it because it has been programmed to decide that 7.1 LPCM, regardless of the incoming format/codec, shall be sent to an audio device when that device is capable of receiving it. The Beam and Arc are capable; there’s no false advertising and the TV does not assume anything - it is told by the audio device over HDMI-CEC all the formats that will be accepted. However, they never state a preference, as you seem to suggest.

As I mentioned, I can’t believe there’s not a setting on the TV to control this behaviour - if there isn’t, I urge you to express your displeasure to LG. Technically, the “Passthrough” setting on the TV should make it feed the input stream directly to the audio device without alteration, though various reports from users on the forum (getting Atmos to play) have made me think at least some TV engineers might have a different definition.

Thanks to @GuitarSuperstar for providing those links! There’s a star in their name for a reason! 

Not to this thread, which is expressly for the investigation of exactly that, and presumably not to anyone who has to tolerate it. I appreciate that you’re trying to solve a problem that you have, but this thread might not be where to do it.

I’ve read all of the many threads on this issue both here and elsewhere and have never seen a report of channels being swapped, only of rear channels missing which presumably was fixed as part of the 7.1 implementation last year. That may partly explain the lack of responses here as people are no longer seeing an issue and so not coming back to the forums.

Yes - it is easy. In all cases, diagnostics report that the incoming stream from the TV is 7.1 McLPCM. We have no reason whatsoever to change the format, nor do we. We don’t even include the software libraries required to do so. The app reports 7.1 because that is what is being fed to the Arc or Beam, from the TV.

I think this is the first time I have seen a response from Sonos that this has in fact been checked and found not to be an issue with Sonos and definitely on LG so that’s useful.

As I mentioned, I can’t believe there’s not a setting on the TV to control this behaviour - if there isn’t, I urge you to express your displeasure to LG

Using passthrough is what causes this issue, the alternative is to use Auto but that has other undesirable effects like converting some input signals to improve compatibility and preventing ‘full’ Atmos from being sent.

However, I’m fairly certain now that with Sonos confirmed to handle 7.1 inputs correctly and to not be incorrectly requesting a 7.1 signal that this is not an issue that impacts the sound and so not something to be concerned with so thanks for that.

I tried this, although I don’t have rear surrounds, just the ARC and sub. the audio file played and I could hear the test voice speak all the channels and they all seemed to play correctly on the ARC.

I was able to test the 7.1 file via AirPlay to my Apple TV 4K. My set up is a LG CX + Beam (Gen 2) + 2 One’s as rears. When the file plays the Rear Surround Left, it comes out of the Rear Left and Rear Surround Right comes out of the Rear Right. The Sonos app shows Multichannel PCM 7.1 

I also did the Uncompressed 7.1 audio test on my Xbox Series X and the same thing happens. The Rear Surround Left comes out from only Rear Left and vice versa. Sonos app does Multichannel PCM 7.1 as well

Uncompressed 5.1 test on Xbox Series X does play out of all the speakers correctly, but app shows as Multichannel PCM 7.1

I do have a PS5 set via LPCM 5.1 giving the Multichannel PCM 7.1 reading as well but did not submit a diagnostic for this one.

I’ve submitted 3 Diagnostics:

• 658268328 - 7.1 audio file via AirPlay to Apple TV 4K
• 1059676763 - 7.1 Uncompressed test via Xbox Series X
• 1377827016 - 5.1 Uncompressed test via Xbox Series X

This is not the case for me. The side channel audio only comes out from the rear speakers.

Hi @slongChez 

Apologies - this was pure supposition on my part, and it turns out I was incorrect. Unfortunately, there isn’t any internal documentation for me to consult yet .

The rear surrounds (LRS, RRS) are mixed together with the surrounds channels (LS, RS) and the result is played solely from the satellite pair, rather than the surrounds channels (LS, RS) being mixed to both front (LF, RF) and the satellites, as I suggested. What you experienced is the expected behaviour.

Apologies again for any confusion.