Multichannel PCM 5.1 dropping out since 14.10 update


Anyone else experiencing the same issue? Multichannel PCM 5.1 blanks out for a second every 1-2 minutes. I don’t think it’s a bandwidth issue as it works flawlessly with Multichannel PCM 7.1 (thorough test) and Dolby TrueHD Atmos (quick test). And it may have been caused by the Sonos 14.10 update. Setup is PS5→ LG C1→ Beam 2 (via earc).


2 weeks ago before the 14.10 update, I watched a bluray film wherein I had my PS5 transcode the DTS-HD MA 5.1 audio to Multichannel PCM 5.1 (as the C1 does not support DTS) and had no issues. Earlier today, I played a bluray film for the first time in 2 weeks and I encountered consistent audio dropouts every 1-2 minutes. It had the same setup where DTS-HD MA 5.1 → Multichannel PCM 5.1. I tested other bluray discs including the one I watched 2 weeks ago and they all now have the same issue.


Curiously, I’ve been gaming heavily on my PS5 the past two 2 weeks and haven’t had any audio issues. Then I realized that I’ve been using Multichannel PCM 7.1 when gaming on my PS5. So I made some changes under the PS5 sound settings to make it output Multichannel PCM 5.1 instead. Lo and behold, I am now getting the same consistent dropouts in games and even on the PS5 main menu.


I think it’s due to the Sonos 14.10 update as that’s the only firmware update I’ve done in the last 2 weeks. No PS5 update, no LG C1 update. Well actually while I was composing this post, I received and applied the latest LG C1 firmware update and I still have the same issue.

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I have an Apple TV-4HD with LG C9 TV and Arc, surrounds & sub and it’s set to default - to output 5.1 multichannel LPCM.

I played the movie ‘6 underground’ from Netflix for 30 minutes or so, just as a test …and that’s all working okay without any audio dropouts.


What settings do you have set on your c9 for audio?

These are my LG C9 TV Audio Settings…

  • Sound -> HDMI ARC (Digital Sound Out = Pass-Through / eARC = ‘ON’)
  • Sound -> Additional Settings (DTV Audio = Auto) / HDMI input format = Bitstream for all HDMI ports.
  • Connection -> HDMI Device Settings (Auto Device Detection = ‘ON’ / Simplink = ‘ON’ / Auto Power Sync = ‘ON’)
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I have no issues with my Arc either, but that’s also not connected to an LG TV, I have a Sony TV. I could hook up my Apple TV to the Arcana/Beam, maybe I can reproduce the issue with that but I don’t think so. Unfortunately I don’t have a PS5, if anyone knows where I can get one, let me know 😀. 

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It seems they fix one thing and break another, I'm looking to replace the Playbar and it's not an ARC straight fight which is unfortunate due to having the Sub etc already.



Yesterday I had finally some time to troubleshoot this. I ended up unplugging the LG to perform a full restart, the PS5 and the Beam2. After that I have been playing with the PS5 for more than one hour with PCM 5.1 as audio output  and I haven’t had a single dropout. Worth trying...

I’m seeing the same issue (Panasonic DP-UB450EB (LPCM) -> LG C1 (eARC) -> Beam2+Symfonisk) when transcoding 5.1 DTS discs in the player. No drops for 7.1 encoded discs. Repeatable switching between 5.1 and 7.1 LPCM on a games console. Occasionally 5.1 LPCM just doesn’t work at all. I tried swapping the Beam for an Amp as per Jay's thread, but of course the Amp is only ARC and therefore no multichannel LPCM to test with.

Frustrating that because LG are being stingy with their codecs (I get it), working around just hits a bug instead. Remains to be proven if this is in LG (v03.33.11) or Sonos (v14.14) or just user error on my part. It’s a narrow use case but it does mean some of my discs will currently only playback (without drops) in down mixed stereo.

Trying to run through this test case though made me think of a couple of gripes where Hifi meets Home Theatre in the same room: 

  • It would be nice to see eARC codecs, some kind of centre speaker configuration and non-Sonance Trueplay on the Amp, which sounded great with standalone speaker frequency range and the wider sound stage.
  • A line in on the soundbars/rears would be convenient for giving legacy components an input into the Sonos ecosystem. Seems odd, expensive and cluttered to need Amp/Speakers or headless port in the same room as a Beam/rears. I understand both the Amp’s and 5’s line in becomes non-operational when configured as rears.  
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Ah, I see. I didn’t realise multichannel LPCM required eARC.

I’m a little confused as to how the fault could be with the TV though if it’s set to just passthrough the bitstream?

Ah, I see. I didn’t realise multichannel LPCM required eARC.

That hadn’t occurred to me either until I tried it, or that the Amp was just ARC. 


I’m a little confused as to how the fault could be with the TV though if it’s set to just passthrough the bitstream?

Presumably the TV shreds the HDMI data stream from the console/bluray and only copies the audio stream to the eARC HDMI port. There’s enough software there for a memory leak or an exception to disrupt the process inside the TV, we know the Beam 2 is reporting the stream drying up. From reading other threads and forums it seems LG have had a difficult time stabilising multichannel LPCM, especially on the 9/X models. Having said that, it doesn’t rule out the Beam provoking the TV into quitting sending data. Would be interesting to know if the diagnostics had shown any kind of handshake during the recovery of the audio drop outs.

My 5.1 dropouts seem to have gone, none for at least 12 hours of music/films/games. Sadly I cannot attribute a single setting to the behaviour change. I decided to test removing the (wireless) surrounds  which did not fix the dropouts, so I added them back to the Beam 2. Then

  • Toggled “Sound Mode Share” out of curiosity (as it was mentioned in another thread) - didn’t notice any obvious change
  • Changed “passthrough” to “auto” - this changed the Beam input type from “Multichannel PCM 5.1” to “Dolby Multichannel PCM 5.1” (whatever that’s meant to be - I’m guessing MAT?). This format however had no dropouts for 10 minutes or so, so I flipped back to “passthrough”, but I don’t remember if the dropouts returned at this point :(

my colleague spotted some issues happening on the CEC network and suggests you factory reset your TV

  • Before factory resetting the TV as my next step (it’s not my main TV so not very inconvenient) I thought I’d try manually switching the devices on from standby instead of using CEC.

Then I noticed the dropouts had gone on “Multichannel PCM 5.1”. I then toggled CEC control on the source devices and the drop outs haven’t come back even when using CEC to standby/powerup .

I’ll try to isolate the steps above if the dropouts return, but I can see why the problem is not wide spread, seems to be a temporary state involving the C1/Beam2, possibly cleared by either the auto/passthrough setting or CEC order.

I can confirm that I am having the same issues on my LG C1 Oled with beam gen 2. The only audio file that I have cut outs with is PCM multichannel 5.1, when playing blu rays on my Sony X700 blu ray player. All other formats work fine, including Atmos. Neither Sonos support or LG support have been able to help. Really frustrating as obviously a lot of blu rays have 5.1 tracks on them and I would rather not have to watch them with standard stereo pcm which sounds as bad as the TV speakers. (Hyperbole).