Dolby 5.1 content outputting as multichannel PCM 7.1 (since LPCM update)

  • 16 November 2020
  • 57 replies
  • 19130 views
L
Userlevel 5
Badge +11

Hi

Thought I would create this thread as a few have reported this issue in the lpcm update threads that are marked as solved so perhaps best to keep it separate.

Issue:

Before the LPCM update last week my sonos arc would receive atmos and Dolby digital 5.1 from the Apple tv 4k box, audio settings were set to the default AUTO-Atmos available.

My LG CX is capable of passing LPCM.

 

Now since the LPCM update with the above settings I still get atmos from apps such as netflix, apple tv + on the apple 4k box, but any content in dolby 5.1 is now outputting as multichannel PCM 7.1, 7.1 being the issue, it should be outputting as multichannel PCM 5.1

 

I have seen similar posts with this issue on the same device and other devices as well.

 

Thank you 

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57 replies

R
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@ledzep1


What happens if you pop an actual 4K disc in?

 

Does it play Dolby Atmos correctly via Passthrough? Also any other disc that doesn’t have Atmos. Does it passthrough?

 

This is a test I can’t perform based on the limitations of my PS5 and lack of Dolby Atmos output. 
 

If it does both those tests correctly via PASSTHROUGH is enabled on your TV then it still points to the physical Apple 4K TV and thin downloadable Apple TV apps we’re all experiencing problems with.

 

If this test doesn’t work using physical media then it very well could be an issue between Sonos Arc and the CX.

 

Still doesn’t takeaway from the other points stated but I’d be interested to know the results of this.

 

L
Userlevel 5
Badge +11

@ledzep1


What happens if you pop an actual 4K disc in?

 

Does it play Dolby Atmos correctly via Passthrough? Also any other disc that doesn’t have Atmos. Does it passthrough?

 

This is a test I can’t perform based on the limitations of my PS5 and lack of Dolby Atmos output. 
 

If it does both those tests correctly via PASSTHROUGH is enabled on your TV then it still points to the physical Apple 4K TV and thin downloadable Apple TV apps we’re all experiencing problems with.

 

If this test doesn’t work using physical media then it very well could be an issue between Sonos Arc and the CX.

 

Still doesn’t takeaway from the other points stated but I’d be interested to know the results of this.

 

Hi

I don’t really understand all your response, but on the Xbox I only play games and I have audio output set to uncompressed 5.1, playing games the Sonos app reports multichannel 7.1

I can play uhd discs fine on my Blu-ray player and get atmos.

It would be nice to get some response from Sonos, they seem very quite on here lately.

R
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@ledzep1

 

I’ll explain.

 

If you have the LG CX set on earc and PASSTHROUGH 

 

When playing a physical 4K Disc in your Xbox (which supports Atmos and HDMI 2.1) and you’ve applied the latest update from Sonos to your Sonos Arc Soundbar / Sub etc 

 

And while playing a 4K disc within your Xbox does it show in your Sonos App under “About” that it is playing in “Atmos” if so great. Now pop in another NON Atmos 4K or Blu-ray into your Xbox - play it - Check in your Sonos App (while playing the NON Atmos movie) and check “About” does it show LPCM 7.1 / LPCM 5.1? If it does that means it is truly passing through. 

 

If it shows LPCM 7.1 MULTICHANNEL or 5.1 MULTICHANNEL that means it is not PASSING THROUGH correctly. 

 

MULTICHANNEL is the key word while Looking at your Sonos App while playing a NON ATMOS movie. If it says MULTICHANNEL then it is not working as it should be. 

 

IF IT DOESN”T SAY MULTICHANNEL that means it is pass through correctly and that the problem lies within the PHYSICAL APPLE 4K TV AND “THIN” APPLE TV APPS PROVIDED WITHIN THE CX AND Xbox and PS5 Apps.

N
Userlevel 5
Badge +7

can someone explain why these are different and what the difference is?

 

  • Multichannel PCM 5.1
  • LPCM 5.1
  • Mutichannel 5.1

 

My brain wants to think those are all the same thing, but apparently its not - why??

SONOS ARC | SONOS Sub | SONOS Play 1 x 2 | LG C9 OLED | PS5 | RTX3090 Gaming PC | Sennheiser GSP600 Headset | Audio Pro T8L Desktop Monitors
R
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@Naekyr 

Their is lots of technical jargon that can go along with it but to simplify it. 
 

If you’re playing something and it says MULTICHANNEL you’re not getting the TRUEST FORM of sound output. 
 

If it says LPCM 7.1 or 5.1 WITHOUT MULTICHANNEL attached to it then your getting the TRUEST FORM of sound possible. 
 

Not to say MULTICHANNEL doesn’t sound good, but audiophiles want PURE PASSTHROUGH SOUND without the MULTICHANNEL gimmick. 

S

@RayCizel 

I believe the fault lies not with Apple TV, but with the Sonos ARC+LG CX combination. The problem with this combo is that they advertise to the client (I have tried PS4 and NVidia Shield TV Pro) as being capable of 7.1 LPCM. However, if one actually sends 7.1 LPCM with passthrough to Sonos, the 2 rear channels will be silent.

On the PS4, this can easily be demonstrated by doing a 360-degree rotation with respect to a sound-emitting object, and the sound will be almost inaudible when the object is right behind you. On the PS4, one can explicitly select 5.1 instead of 7.1 so that the PS4 will only send 5.1 sound-mix to Sonos. The 360-degree test will now sound normal.

On the nVidia Shield TV however, there is no option to choose 5.1 -- this creates a problem in apps/games that output 7.1 channels.

This issue is now being tracked in the following thread:

https://en.community.sonos.com/home-theater-228993/ps4-pro-outputting-pcm-via-lg-cx-shows-multichannel-pcm-7-1-for-sonos-arc-but-rear-surrounds-have-no-audio-6850771

Note: this has nothing to do with Dolby-encoded signals (DD, DD+ or TrueHD, with or without embedded Atmos), which can be correctly decoded and played by Sonos. This also has nothing to do with HDMI 2.0/2.1 -- assuming that both the TV (LG CX) and Sonos ARC have already been properly connected with HDMI 2.1 eARC.

Corry P
Userlevel 7
Badge +18

 Hi Everyone,

Well, this is embarrassing!

After some investigation, I’ve found that downmixing of 7.1 channel LPCM to 5.1 channel LPCM was indeed implemented on the Arc as a feature last year, but our literature wasn’t properly updated to reflect the change.

To be clear, the Arc does downmix 7.1 LPCM to 5.1, has done for some time, and we are working on updating our documentation to reflect the fact. Beam (Gen 2) has always supported LPCM and has always downmixed.

Thank you all for pointing this out to me so we can now make sure that this information becomes public. I’m sorry for the unnecessary confusion. I’ll post this in multiple threads.

This other issue with LG TVs is unrelated, but we’d very much like to get on top of it. We’ve requested the investigation of LPCM channels being played from the wrong speakers when an LG TV is involved, specifically when 7.1 channels are reported, and we will reach out to LG with details once we’ve gathered some solid evidence for them. Therefore, we’d very much appreciate it if anyone affected by this specific issue would visit this new thread I’ve made for gathering some details. Thank you.

 

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