Question LG TVs -- Auto or PassThru for HDMI ARC audio?

Clem_Dye

Distinguished Member
I ask the above, as my LG 49SM8500PLA TV, which I've had for about a year or so, routinely throws two hissy fits (not at the same time, from what I've noticed):

1) It flags Freeview channels as having 5.1 audio, which is wrong (ITV HD, C5HD, Talking Pictures, etc.)
2) Stuff flagged as having 5.1 audio on Amazon Video and NowTV only plays back in stereo

My TV is connected to a Yamaha YSP4100 sound bar. My first thought, given that the bar is perhaps 10 years old, was that it was starting to fail. However, all other sources connected to it work fine, and a power cycle, when the LG was mis-flagging audio, made no difference to the problem.

I can clear both (1) & (2) by removing mains power to the TV, but it's a hassle trying to unplug and plug-in cables (the proverbial rats' nest, that we all know and love).

The last time that problem (1) happened, which was earlier this week, rather than bouncing the TV's power, I toggled the HDMI ARC setting from Auto to PCM and back again, which seemed to fix the issue. At that point, I did wonder if I should be using the PassThru setting rather than Auto. The only other bit of kit connected to the TV that supplies 5.1 audio is a NowTV box. The TV seems to have no problem routing audio from the box into my soundbar.

For problem (2), the next time that this happens, I'll also try toggling the HDMI option, and I'll also force quit the offending app. to see if I can avoid pulling power.

I suspect that a previous firmware update might have introduced the above issues, as for the first 6 months or so the TV and bar combination was fine. That, or I have marginal hardware or a weird fault somewhere. I further suspect that the two problems are somehow linked, given the audio switch around, but I've never investigated the two issues at the same time, having always pulled the TV's power when one or other surfaces. Anyway, I'd appreciate any LG TV owners thoughts on the above problems. Is PassThru a better bet? Has anyone experienced the same or similar issues? Any insights would be greatly appreciated.

Cheers.
 
Last edited:

marcd5123

Well-known Member
Hiya @Clem_Dye as you know I own a 55SM8600 my self scene March 2020 this year.

Okay let's see Reading your post... Well iv always had my sound setting set as "pass through" it's less CPU work for the TV plus why do I need the TV to do all the work as I have 2015 Denon X4100W that can do all the decoding work it's self I paid £1.3k for the bugger so it should do it all 👍😊...

Yes I too have had issues with my 55SM8600 doing a so called "hissy fit" btw I love that term... Iv had it happen every now and then. To be honest I had it happen on my previous 2017 49SJ810V that also used to do it.

I personally put that down to it being a computer. I work in the IT industry my self and an IT engineer my self so I'm used to it. These TVs are essentially PCs they have pretty much all the ussal elements of a PC with a large screen.

If my TV was do pull a hissy fit and restart each day or several times in one day or just to many times in a few consecutive days then I would worry somewhat more.

I had a and now keep it as a spare Amazon 4K Firestick and that also would crash now and then it reset it self out the blue. Iv recently upgraded to the new Amazon 4K Fire Cube and love it to bit absolutely awesome power peace of kit.. But in the few weeks iv had that it has reset it self a few times, but that's been now and then again it's a PC so I tend to view it that way.

Yes, I digress with regards it being a software /firmware issues possibly 🙄... I tend to find that firmware updates tend to solve some issues and then flag up others. It's not just LG the same goes for Sonys as well I used to own one. It's in their nature to behave this way to be honest.

Unless it gets ridiculously bad I would not worry to much as for the sound problems iv not had any to note my self so far anyway. All decoding is and has been done correctly that I can see, I also use freeview and Denon does as it should that I can see.
 

Clem_Dye

Distinguished Member
My testing so far using Freeview is that PassThrough works correctly for 2.0 and 5.1 material. I haven’t yet tried any of the streaming apps. or the NowTV box. Talking of hissy fits, the TV decided to turn itself off this evening after about 20 minutes use. It’s done that before — this will be the 5th time since I’ve had it, from memory.

I think that post lockdown, I’ll look to replace it. It’s been by for the flakiest TV that I’ve ever owned. Now that 2020 Sony TVs have the NowTV app. I think that’s what I’ll be going for.
 

Clem_Dye

Distinguished Member
Well, I’m still experimenting with the options. Auto and Passthru do make the Netflix app. behave differently. If I have the LG set to Auto, when I fire-up Netflix, my soundbar switches to 5.1. Everything that I then watch is played back in 5.1, regardless of source audio — 5.1 is 5.1, but stereo stuff also plays back in faux 5.1, even when I check the stream info., which confirms a stereo stream.

If the LG is set to Passthru, when the Netflix app. is started, my soundbar is set to stereo. Watching 5.1 material switches the bar to 5.1, and when I stop, it switches back to stereo. However, 2.0 stuff still plays back as faux 5.1.

If I use and external source for Netflix and the TV is set to Auto (I’ve yet to test Passthru) 2.0 and 5.1 audio is rendered correctly. Hopeless!
 

Clem_Dye

Distinguished Member
The NowTV app. seems to deliver 5.1 audio with the TV set to Passthru. Amazon is my next port of call. I also need to watch an English language BR to check for any lip sync oddities, although BR audio isn’t routed via the TV.
 

next010

Distinguished Member
Yeah that is strange behavior, LG don't explain it all in the manual. Tour list of settings->sound->digital sound out is the most you get.

As far as I understood it the pass-through function is for use with eARC.

Prior to its introduction, the Auto was for ARC and PCM for stereo.

So what pass-through does on a non-eARC TV is a bit of a mystery, it might be bugged/broken given the behavior you have outlined.
 

Clem_Dye

Distinguished Member
I suspect there’s something amiss with the software, rather than a fault per se. When I bought my TV last year, Currys were doing a model that was £200 more. It was basically the same TV but it had eARC support. It seems to be performing better with Passthru enabled, rather than Auto, with the exception of the Netflix faux 5.1 audio on stereo sources. Odd. Post lockdown, I’ll be looking to replace the TV, as much as I like it. It’s too flaky.
 

SeeMoreDigital

Well-known Member
As far as I understood it the pass-through function is for use with eARC.
I suspect there’s something amiss with the software, rather than a fault per se. When I bought my TV last year, Currys were doing a model that was £200 more. It was basically the same TV but it had eARC support...
The LG televisions HDMI eARC 'pass-through' mode should indeed do what it implies, which is to pass-through any audio format type including lossy and lossless DTS bit-streams and multi-channel PCM.

This lack of full functionality, lets down the 2020 range of TV's...
 

marcd5123

Well-known Member
The way I see it..is quite simple from what I understand without having to over complicate things..

Passthrough is just doing as the name suggests it's passes through the "raw" bitstream data Stright out the TV via the HDMI-ARC channal without it being decoded by the TV. That's the entire point of Passthrough to send the Raw bitstream data out the TV via the HDMI-ARC channal to an appliance in this case an AV AMP that can handle and decode that raw bitstream data it receives.

That's it simple. Auto or PCM is just that you tell the TV how to handle the data. whether it's ARC and or e-ARC.

That it... Iv had my 2019 55SM8600 for 8 months now with it set to Passthrough to my 2015 Denon X4100W AMP and not once have I ever had any issues with decoding material. That's either with Freeview or Prime Video or Netlfix or Disney +. Britbox. I also have a stack of 4K HDR10 films on my Ext USB 3.0 HDD as MKV files and once agian every film I have watched all decode correctly no problems what so ever and that's plugged into the correct USB HDD socket at the side of the TV. The PVR function also works correctly.

And that's either using the TVs own built in apps or what I mainly use was Amazon 4K Firestick up until recently I upgraded to Amazon 4K firecube and that decodes perfectly fine.

This is also with the latest firmware update from this year June 2020.

If you are having issues then do a factory reset if that does lot work then theirs either a fault with the TV or the recipient device handling the bitstream data coming in.

From memory I have Now TV for a short while this year with the added so called rip of Sky boast to get 1080p and 5.1 and when I used that for 1 month that worked perfectly fine and agian decoded correctly. 😊👍
 

Clem_Dye

Distinguished Member
The LG televisions HDMI eARC 'pass-through' mode should indeed do what it implies, which is to pass-through any audio format type including lossy and lossless DTS bit-streams and multi-channel PCM.

This lack of full functionality, lets down the 2020 range of TV's...
Yes, I get that, but my TV only has ARC, not eARC, although the principal is the same. If using Passthru fixes my issue, then all well and good!
 

marcd5123

Well-known Member
Hiya @Clem_Dye Yes mine has ARC all 2019 models have ARC apart from the 9 series then it's eARC. Sorry I meant either ARC & eARC. Btw I did post yesterday theirs a new firmware update out. Iv done mine already. 😊👍
 

Clem_Dye

Distinguished Member
New firmware, just as we head into another lockdown? Oh great. If the update bricks your TV then there’s no chance of a repair. Nice timing, LG. Not.
 

Clem_Dye

Distinguished Member
Looking at the readme, it seems to be all about ads., nothing about any real improvements, like Atmos support from the ATV app. I won’t be rushing to install this update. Luckily, my TV hadn’t started nagging me about it yet.
 

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