Sonos Staff

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

Forum|Forum|4 years ago
April 11, 2022
75 replies
11342 views

Hi,

We want to gather some details from people experiencing issues with playback of 7.1 LPCM audio streams on a Sonos Arc or Beam (Generation 2), via an LG television set. Specifically, when channels are playing from the wrong speakers - for example, but not limited to, if you hear dialogue only coming from the rear speakers, consistently.

If you have experienced this channel mis-mapping, please provide, in this thread, the following details:

Your LG TV model number

Your media source device name and model number or TV app that the issue was noticed on, and the name of the movie/show that was affected

Models of any other HDMI devices connected to the TV (if applicable)

The confirmation number of a Sonos system diagnostic submitted while the affected media was playing and 7.1 LPCM was reported in the Sonos app.

Thank you for your assistance.

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slongChez

Trending Lyricist I

Hi @slongChez

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.

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

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.

Thanks for clarifying this Corry! Curious to what the results from the diagnostics return back.

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rbouley

Contributor I

Mine does this as well. Multichannel PCM 7.1. Happens on my PS4 Pro when watching Blu-Ray's and my Nintendo Switch.

I notice the center channel sounds left oriented and the right side sounds very hollow.

LG C1 55" Passthrough, eArc enabled.

Devices connected: Sonos Arc, Nvidia Shield Pro, Nintendo Switch, PS4 Pro.

Sonos Arc, Sub, two One's.

Diagnostic: 368466851

Corry PAuthor

Sonos Staff

Hi @slongChez

All 3 diagnostics show 7.1 LPCM being played - although not normal, this is what we now expect to see from an LG TV.

Hi @rbouley

You may want to try retuning TruePlay, if you have it activated.

Settings » System » [room name] » TruePlay » TruePlay Tuning.

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

Mutiny

Trending Lyricist I

LG CX + Beam Gen 2 + PS 5 here.

When switching to PCM on console the app shows Multichannel 7.1. Sound feels flat, volume is low and it feels like i am losing surround too, not sure how to describe it.

Compromising to Dolby or DTS on console gives me the best result though, sound difference is quite amazing. Not sure of how much of a “compromise” it is from a technical standpoint, but it is what it is.

Diagnostics - 1015551901.

Thank you very much for looking into this!

Hope this helps!

Corry PAuthor

Sonos Staff

Hi @Mutiny

When switching to PCM on console the app shows Multichannel 7.1. Sound feels flat, volume is low and it feels like i am losing surround too, not sure how to describe it.

This is probably expected - as I mentioned earlier, I have a Samsung BluRay/Amplifier, and if I play 7.1 sources I need to crank up the volume, often to twice that I’d use on another source. It should sound more tonally balanced once you turn up the volume. If it’s not to your liking, all I can suggest is to not use the PCM setting.

Compromising to Dolby or DTS on console gives me the best result though, sound difference is quite amazing. Not sure of how much of a “compromise” it is from a technical standpoint, but it is what it is.

Apart from the difference in dynamic range - which you’ve already noticed and can be a hindrance when not in a cinema - you’re unlikely to be able to tell the difference in quality. Dolby and DTS are lossy formats, so some information is thrown away during the encoding process, but the codecs are engineered so that the lost information is restricted to being related to sounds that you are unable to hear anyway. You are unlikely to be able to tell any qualitative difference unless in a direct, switching-back-and-forth-between-streams comparison. It’s important to note that if the original source doesn’t have an LPCM stream, meaning the LPCM stream is the result of the decoding of a compressed stream, then there is no difference in quality - only in where the decoding is done.

With that out of the way, it does seem that quite a few people are misunderstanding what it is we’re looking into here. If your Sonos app is reporting 7.1 LPCM when a different source audio is selected, that’s because your LG TV is choosing to decompress the compressed stream into LPCM, rather than allowing the audio device to do it. It’s a bit strange, to be sure, but there is nothing we can do about it - only LG can address this behaviour. Nor is there anything to be investigated about it - we are aware and we understand the technicalities of it, if not the why.

It seems that no-one actually has mis-mapped channels to report, which is fantastic. As this thread is now more off-topic than on-topic, I’m going to close it soon. If anyone does have mis-mapped channels to report after this thread has closed, please DM me.

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

Corry PAuthor

Sonos Staff

Hi All,

We feel it’s worth pointing out that, from a technical standpoint, there’s nothing wrong with LG sending a 6 channel stream via an 8 channel mapping - nothing is lost, and all channels appear to be playing from the correct speakers. We don’t view this as a fault that needs to be fixed, just a more unusual choice made by LG in this case.

When Sonos is given the opportunity to do the decoding, however, we will apply a gain boost to increase the volume, which is why DTS or DD will sound louder than LPCM. LG’s converting to LPCM may well be an attempt on their side to homogenise the volumes across various sources and compression types.

In the end, it’s really up to you, the end users, and what you prefer to listen to.

It does seem strange to me that the Passthrough setting on the TV does not seem to actually passthrough - this still might be something you’ll find worth reporting to them.

I hope this clears things up.

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

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ste_ms

Enthusiast I

It does seem strange to me that the Passthrough setting on the TV does not seem to actually passthrough - this still might be something you’ll find worth reporting to them.

It would be useful if Sonos could also report this to LG as I expect there would be a much higher chance of them actually looking into it and ultimately it would be to your benefit to have this resolved assuming LG TVs default to this behaviour with their new models going forward - less questions and support calls etc.

Airgetlam

I’d think the opposite. There’s no financial relationship between the two companies, so I would expect LG to listen more to people who have actually spent money with LG, rather than some random third party providing a competing product to their own sound bars.

Bruce

S

slongChez

Trending Lyricist I

Hi All,

We feel it’s worth pointing out that, from a technical standpoint, there’s nothing wrong with LG sending a 6 channel stream via an 8 channel mapping - nothing is lost, and all channels appear to be playing from the correct speakers. We don’t view this as a fault that needs to be fixed, just a more unusual choice made by LG in this case.

When Sonos is given the opportunity to do the decoding, however, we will apply a gain boost to increase the volume, which is why DTS or DD will sound louder than LPCM. LG’s converting to LPCM may well be an attempt on their side to homogenise the volumes across various sources and compression types.

In the end, it’s really up to you, the end users, and what you prefer to listen to.

It does seem strange to me that the Passthrough setting on the TV does not seem to actually passthrough - this still might be something you’ll find worth reporting to them.

I hope this clears things up.

There’s some weird things going on with Passthrough for sure. If I set it to Auto, my Xbox won’t give the options for Uncompressed 5.1 and 7.1. If set to Passthrough, the options are available again.

I’m guessing it’s just best to leave it set to Auto instead of Passthrough if it isn’t doing what it’s supposed to.

S

spacegrass

Lyricist III

LPCM 7.1 and 5.1 with ATV4K and LG TV Mis-directed channels Issue - Revisited

Old thread, but I just recently added rear surrounds (Ikea Bookshelfs) to my LG C1/Sonos Arc SL/ATV4K (2021) set up, and have since had multiple occasions where the sound from the ATV4K 5.1 source (being Prime, Netflix, and AppleTV+) is coming out the wrong channel - the main dialogue comes from the one or the other rear surround instead of the Arc SL). It is intermittent, but does keep happening. The channel mis-assignment can be “fixed” in the moment by power-cycling (unplugging) the LG TV. The ATV4K source also consistently shows as “multichannel 7.1” in the Sonos app, when it is of course a 5.1 PCM feed from the ATV. I have the audio settings for the LG C1 set to “bitstream”, “enable eArc”, and “passthrough” and ATV4K set to “Atmos/Auto”. When the source is from apps on the TV itself, “multichannel 5.1” displays correctly in the Sonos app, and there is no channel mis-assignment.

I know that this is an LG/Apple issue, and not a Sonos issue, but I am raising it here now because @corryp sought evidence of this “wrong channel” behaviour, and it did not appear anyone reading the forum at that time was experiencing it. I took a diagnostic when it happened today (main dialogue from right rear speaker) – watching Netflix via the ATV4k – number 538943573. No need to post “so what is your question?” - i don’t have one - this is fyi for Sonos.

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