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Dolby Digital 5.1 voice track coming from rear surround speaker

  • 24 December 2023
  • 5 replies
  • 311 views

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In the past few weeks the vocal track of Dolby Digital 5.1 sound has been only coming out (loudly) of the left rear surround speaker of a Sonos Arc System.  No voices come from the Sonos Arc, but it sounds like surround speaker sounds are coming from the Arc.  So shows in DD 5.1 are basically unlistenable.

My system: 1) Sonos Arc/Sub/2 Sonos One surrounds, 2) LG CX  77 TV, 3) Apple TV 4K 3rd gen

I stumbled upon a fix, which is to toggle eARC off and back on again on the LG CX.  After than sound comes from the Arc, but eventually this has be redone (see below). 

Why is this happening and is there a better fix? This is a new problem that started a few weeks ago.

Further details:

  • To play DD 5.1, I have to explicitly set Apple TV’s audio format to DD 5.1 because when you set it to “Auto, Atmos Available” you get Multichannel PCM 5.1 which sounds bad.  This is a known limitation of Apple TV (https://en.community.sonos.com/home-theater-228993/apple-tv-unable-to-switch-dolby-formatting-with-arc-6869224 ).  Voice correctly comes from the Arc with Multichannel PCM 5.1, but voice incorrectly comes from the left rear surround with DD 5.1
  • My fix of toggling eARC on/off works, but when you change Apple TV’s audio format to “Auto, Atmos Available” and back to “DD 5.1” then voice starts coming out the left rear surround speaker again.  It’s a pain to have to keep doing this, but better than having to listen to lower-quality multichannel PCM 5.1 instead of DD 5.1
  • Rebooting Apple TV doesn't help.  Removing/reinstalling surround speakers in Sonos doesn't help.
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Best answer by AjTrek1 24 December 2023, 22:39

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5 replies

Userlevel 7

Hi

First

  1. I recommend that upon the next occurrence you submit a diagnostic and post the reference ID in your next post. After the Christmas holidays call Sonos tech support to see if the diagnostic showed any anomalies.

Self-Trouble Shooting while waiting to contact Sonos Tech support

  1. Check HDMI cable connections between Arc and TV. 
  2. If they are seated properly I next suggest trying another HDMI cable and/or purchase a new one if necessary. We need to rule out the HDMI cable as the culprit. 
  3. Repost with results
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I recreated the audio problem and submitted diagnostic info to Sonos, reference ID 390130577.  I then toggled eARC on/off which fixed the problem and created a second diagostic report, reference ID 690079339.

The HDMI connect to the Arc is secure. Checking the TV is problematic. The “professional” installers of the LG 77 CX installed it to the wall in a way I can’t remove myself to check the cables. So I can’t check that without having an installer come to the house. 

However, I am able to reproduce and fix the problem every time so I doubt the cable is the issue.  All I have to do is set Apple TV Settings > Video and Audio > Audio Format > Change Format Off (Auto, Atmos Available) and then change it to On (DD 5.1).  Vocal track then comes from the Sonos One left rear surround speaker.  Toggling LG CX TV eARC off/on corrects the audio problem.  

 

 

Userlevel 7

Hi

OK...assuming your:

  • Sonos Home Theater (HT) is setup properly
  • You haven’t turned off the WiFi radios in any Sonos component associated with your HT
  • You haven’t made changes to your network
  • Try the following:

LG CX TV

Check LG for updates 

LG audio is set to Pass through

AppleTV

  • Check for updates

AppleTV Audio

  • Audio Out Default > TV Speakers
  • Audio Format > Auto (Dolby Atmos Available)
  • Audio Mode > Auto

AppleTV Airplay and HomeKit

  • Airplay > On
  • Allow Access > Same Network

UnPlug

  • TV
  • Sonos Arc, Sub and surrounds
  • Any other Sonos products
  • AppleTV

Reboot Router and let it come back

Plug-in

  • TV
  • Sonos Arc, Sub and surrounds (let all components come back)
  • Any other Sonos products (let all comeback)
  • AppleTV

Test your system

I have the same problem. Is there a fix which isnt only temporary? I habe a LG C2 with the acr, sub 2 and 2 one sl and the Apple TV 4K.

Userlevel 7
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I have the same problem. Is there a fix which isnt only temporary? I habe a LG C2 with the acr, sub 2 and 2 one sl and the Apple TV 4K.

As far as I know there‘s a problem of some LG TV models with multichannel pcm audio. The audio information gets a kind of a wrong channel information so that in the end for example center signals are in the rears. 
I think that just can be fixed with a firmware update from LG. 
As AppleTV with standard audio settings sends DD5.1 as multichannel pcm this could be the reason. If ATVs audio settings are set to force DD5.1 ist should work fine.