Lossless/HD audio on LG CX from HDMI sources over eARC is broken
I received my 77" CX a week ago and up until last night I couldn't get lossless HD audio over eARC from HDMI sources connected directly to the CX including my Xbox One X, PC, PS4 Pro and Nvidia Shield.
Thinking that the culprit for not getting lossless audio over eARC from HDMI sources might be a HDMI handshake issue, I turned off my CX from the power outlet and after doing so I was able to get proper uncompressed DolbyTrueHD flavour of Atmos from the Xbox One X's Bluray player and in Atmos supported games. No stuttering and no Dolby Digital+ compressed garbage.
HOWEVER it is extremely flaky as whenever I turn off the Xbox One and turn it back on or or switch over to a different source device and then back to the Xbox One X input it goes back to Dolby Digital+ based Atmos. I discovered that turning off eARC and turning eARC back on again within the CX's sound settings brings it back to uncompressed LCPM 7.1/Dolby TrueHD based Atmos. To rule out the possibility of either the AVR or the cables being the culprit, I tested this on two different eARC capable AVRs including my Sony STR-DN1080 and Denon X3600H in addition to a range of HDMI cables which include Belkin's 48Gbps rated HDMI cables and had the same issue.
I also tested this with various different HDMI devices from Xbox One X and PS4 Pro through to the Nvidia Shield and PC and had the exact same issue with the CX's eARC not working properly until I disabled and re-enabled it within the TV's audio settings.
My hunch is this has all to do with the way the CX handles LPCM audio as that is what the Xbox uses to decode into Atmos (the readout on my AVR confirms this when I first boot up the Xbox displaying LPCM 7.1 before switching to DolbyTrueHD Atmos). And before anyone asks, yes I am using the latest firmware version 03.00.60, which supposedly enables MC-LPCM on the CX series but as my testing reveals, it is extremely flaky over eARC.
I applied the same solution on my HTPC and was able to get uncompressed Atmos but as was the case with the Xbox One X, switching it to another source or turning off the PC and back on again will default back to Dolby Digital+ requiring me to have disable and re-enable eARC within the TV's audio settings.
There's plenty of people on AVSForum reporting the same issue as well. Is LG working on a firmware update to fix this ongoing eARC issue?