#hdmi-arc

First off, let me state that in my opinion a guide like this shouldn't be needed. The whole point of HDMI-ARC is that you connect your ARC-compatible TV and soundbar with via a single HDMI cable and you're done. Sadly nothing ever works like it's supposed to, so here we are.

I recently upgraded my game room TV from a Sony XBR 49X800D, a 4K 49-inch LCD TV with middling HDR and black level performance, to LG's latest and greatest 48-inch OLED48CXPUB. I hated the black levels on the Sony XBR and wanted all the latest HDMI 2.1 features that the LG CX supports, including Variable Refresh Rate and Auto Low Latency Mode for use with my Xbox One X. I also wanted a "future proof" TV that can support 4K 120 fps when the Xbox Series X shows up later this year.

My sound system here is a Vizio SB36514-G6 36" 5.1.4 soundbar. I watch a lot of 4K UHD Blu Ray movies on my Xbox so I wanted a sound bar with Dolby Atmos and included both front and rear upward firing speakers. It also had to fit in my game TV cabinet so the 36-inch size is perfect, which is also the reasons I selected the LG CX as it’s the first 4K OLED under 50-inches.

It all has to fit in here

The CX doesn’t disappoint at all in picture quality - it blows away the Sony LCD and VRR in Xbox games is fantastic. Until I noticed the horrendous 500 millisecond audio lag with Xbox games and apps with my default Dolby Atmos audio output setting.

Originally with the Sony TV I had the Xbox HDMI output hooked directly to the Vizio soundbar and passed the video through to the Sony. The Sony has HDMI ARC but doesn't pass Dolby Digital or Atmos audio, and since it also doesn't support HDMI 2.1 it was fine to just let the Vizio pass the video through while it directly decoded the audio stream.

However with the LG CX the only way to take advantage of all the great HDMI 2.1 features is to connect the Xbox One X directly to the LG CX and then use HDMI ARC for the LG to pass the audio to the soundbar. The LG passes Dolby Digital and Atmos bitstreams through ARC, so it seemed the perfect solution.

I soon noticed the lag between the picture and the audio when playing Xbox One X games. Running test patterns in the Xbox Netflix app confirmed there is about a 500 millisecond audio lag with Atmos turned on.

And then there's the issue of the LG CX not passing DTS audio. I was a little surprised how many of my 4K UHD Blu-ray discs actually only have a DTS audio soundtrack, no Dolby Digital or Atmos. Even though my soundbar can decode all DTS formats, the LG TV wouldn’t passthrough the DTS bitstream.

So after a lot of experimentation with settings both on the TV, the Xbox, trying different combinations of cabling, here's what I found to be the optimal configuration settings if you want to use HDMI ARC with your LG CX and Xbox One X:

Connections: • Xbox HDMI to LG CX (use input 1, 3 or 4, save input 2 for Soundbar HDMI-ARC) • LG CX HDMI 2 to Soundbar HDMI Input

(Be sure to use HDMI High Speed cables, preferably certified for HDMI 2.1)

LG CX Settings: • Set Sound Out to HDMI-ARC • Set HDMI Audio Input Format to Bitstream • Set Digital Sound Out to Passthrough

Xbox One X Settings: • Playing Xbox Games and Apps (Netflix, etc.)      ○ Go to Settings > General >Volume & audio output      ○ Under Speaker Audio           - Set HDMI Audio to Bitstream Out           - Set Bitstream Format to Dolby Digital This will reduce the audio lag to 200 milliseconds or less, which isn't perfect but is acceptable. If you set the Bitstream format to Dolby Atmos for Home Theater you will get 500 milliseconds of lag which produces obvious lip sync and late audio cues. If you can live with it then by all means you can set this to Atmos, but I couldn't. 

• Playing 4K UHD Dolby Atmos Audio Blu-ray Discs      ○ Go to Settings > General >Volume & audio output      ○ Under Speaker Audio           - Set HDMI Audio to Bitstream Out (same as above)           - Set Bitstream Format to Dolby Atmos for home theater      ○ Go to Settings > Devices & Streaming > Blu-ray           - Select/check Let my receiver decode audio

With these settings the Xbox One X plays Dolby Atmos 4K Blu-ray movies in perfect sync with the full glory of Atmos sound. This leads me to believe the lag issues with Xbox games and apps when Atmos is turned on is a byproduct of the Xbox itself, something its doing in its Atmos processing. If that's the case, maybe this will be resolved with the dedicated audio processors in the upcoming Xbox Series X.

• Playing 4K UHD DTS Audio Blu-ray Discs      ○ Go to Settings > Devices & Streaming > Blu-ray           - Uncheck Let my receiver decode audio (the opposite of above) The LG CX isn't licensed to pass DTS audio through to your soundbar via HDMI-ARC. It is an incredibly annoying cost-cutting measure LG took considering their 2019 B9 and C9 TVs included DTS passthrough. But fortunately the Xbox One can transcode DTS on the fly into a Dolby Digital signal that can be passed over HDMI to the LG CX which in turn passes it to the soundbar which then decodes it. I tried changing the Xbox to use uncompressed 5.1 audio and changing the LG CX to pass PCM audio through but I couldn't get it to work. Simply unchecking the Let my receiver decode audio is the quicker, simpler solution anyway (less settings to change between gaming and watching a 4K Blu-ray). I tested this with The Fate of the Furious (don't judge) and the sound mix was excellent with plenty of action in the rear speakers and clear dialog via the center channel. 

Now there is one other option for Xbox games, apps and non-Atmos 4k discs and that's connecting an optical audio cable from the Xbox to the soundbar (assuming your soundbar supports optical audio; my Vizio does). This will actually give you perfectly synced Dolby Digital 5.1 audio for games and will pass through DTS soundtracks for the soundbar to decode natively since you’re bypassing the LG CX entirely for audio.

I ruled out connecting the optical cable for me as it just complicates the settings when you need to change them. On the Xbox you'd need to turn off HDMI Audio, turn on Optical Audio, and then switch the soundbar to the optical audio input. Then when I want to use the LG CX native Netflix app (which supports Atmos!) or use my NVidia Shield (which has no audio sync issues, by the way) I'd have to change the soundbar input from optical to HDMI, and if I want to watch an 4k Atmos Blu-ray disc on the Xbox I have to reverse all the optical settings back to HDMI. Sticking with HDMI lets me change just one setting between playing games and watching an Atmos movie on the Xbox (Dolby Digital to Dolby Atmos for Home Theater); for me the simplicity of that is worth living with the 200 millisecond audio lag with Dolby Digital in games over HDMI-ARC. And don't forget, the Xbox Series X won't have an optical audio output port, so that won't be an option on that console.

Something else that may help all of this is eARC, or Enhanced ARC. HDMI eARC supports the higher bandwidth of the HDMI 2.1 specification and should improve support for Dolby Atmos. The LG CX supports eARC (another reason I chose it), but so far I can't find an eARC soundbar under 43-inches wide with wireless upward firing rear speakers (having both front and rear upward firing speakers makes a huge difference with Atmos in my opinion). HDMI eARC is brand new so I'm hoping later this year there will be more choices available.