This is a common problem obviously. In searching for the solution you find a lot of people guessing. It would help if manufacturers would add just a little description with just a shred of evidence as to how something is supposed to work in their documentation. It is insulting actually as they go overboard in dumbing down the documentation clearly assuming that we do not have have the capacity to understand. They intentionally (at least I think intentionally) withhold the information, the logic, that you might need to problem solve or otherwise get the most out of your purchase. Let me describe what I have found relative to the 84LM9600. You can already guess that the documentation is useless.
So you are watching a movie which starts out great but after a while something doesn't seem right with close-up facial scenes and dialog. You realize that your surround sound is not synchronized with lip movement. Now that you have noticed this it becomes annoying and you are distracted from the plot. What is going on? How can you fix this?
The problem occurs because it takes time to move and process video frames from your HDMI cable to the display. That much you will read elsewhere. It also takes time to process the audio but generally not nearly as much. Inside the panel the manufacturer knows how much delay there is in their video presentation. There are timing signals that they can use for this. They can delay the associated sound appropriately so that from the internal speakers the audio is synchronized with the video no problem.
But if you run the audio through an external system, you add a variable to the equation that the display panel cannot automatically account for. If you run audio from the panel through an amplifier or receiver you can again delay the sound such that you can see the explosion on the screen before the concussion hits from your subwoofer. If you run the video through an A/V Receiver before it reaches the display (like I do), you will produce the sound before the image giving you the feeling that you know what is coming before you see it.
These delays are inevitable. They can reduce them with faster hardware and more efficient processing but they cannot eliminate them. It is not the length of your cable or the distance from your speakers. There are delays with both but those are the order of of microseconds or less. What you are experiencing though can be on the order of hundreds of milliseconds.
Alright, I obviously ran into this immediately. Having replaced a rear projection set (Pioneer PRO-710HD) with the LG 84LM9600 4K panel, I probably went from practically undetectable delay to what might be worst case (assuming that upconverting and displaying 4K is a lot more work than displaying standard HD).
Here's my set up:
Oppo BDP-103 Blu-Ray ====(HDMI)====> Pioneer Elite VSX-21TXH AVR ====(HDMI)====> LG 84LM9600 Panel
The video image experiences a progressive delay. It starts out synchronized (well call it matched closely) but after several minutes it is clearly out of synchronization. After a half hour you have stop and reset something to realign the sound with the picture.
The LG Panel has a menu option to enable "Audio Sync". Further they give you the ability to adjust (plus or minus) the audio delay separately for the internal and SPDIF (external) speakers. The range is from -5 to +15. I am not sure of the units but my guess would be frames of video and that a positive setting further delays the audio.
This is useful if you are amplifying the audio output from the panel processing the sound after
the panel. In this case you likely have a fixed delay in your audio system that you can now account for by adjusting the audio timing in this menu by a couple of frames (30 frames/sec assumed?) to the negative.
However this is NOT the adjustment that you need if you are extracting the audio before
the panel and playing it through your surround sound system.
Now in the AUDIO PARAMETERS menu on the Pioneer receiver you can adjust the audio delay in tenths of a frame from 0.0 to 10.0 frames. This is a fixed delay and as I mentioned the sound to picture delay is progressive. It continually increases. If you are up for a challenge, and I tried this, you can keep adding delay as your movie progresses. That works but after a while you can actually hit the 10 frame limit of the setting. It is also annoying in that making any change to this parameter briefly interrupts the audio eliminating any stealth that you might have in mind in trying to hide your effort from your audience.
Any acceptable solution to this MUST be dynamic. This is such a major issue that you know there has to be the solution, somewhere... right?
So further down in the AUDIO PARAMETERs menu on the AVR there is a AUTO DELAY setting (actually A. DELAY) where you can turn this ON/OFF. In my case it was ON! Wait a minute! ON?? So what does this do then? It clearly isn't addressing the audio synchronization that I am seeing. But if you read the manual it seems to imply that the purpose of this is the synchronize the sound with the picture. It was clearly not doing that.
This is what they don't tell you anywhere. How can the AVR synchronize the audio with the picture? How does it know what you are seeing on the screen to do that? It needs some kind of feedback from the panel. What it needs is an audio feed from the panel even though you are not going to play that sound. It can use it automatically delay the processed surround sound audio to synchronize with the stereo audio from the TV (assuming that the panel manufacturer already has done that internally). That's how I would implement it. I can't find this in writing although maybe someone out there can post what they have read. So I decided to verify the hypothesis by connecting the panel's audio output back to the AVR.
In the SOUND SETTING menu on the LG 84LM9600 you can enable ARC. This enables an Audio Return Channel for the HDMI-1 connection. This is a new standard apparently where the panel can send its audio back to the video source. Hmm... why?... Well apparently to support any automatic auto delay function. In this menu you can also turn off the TV SPEAKER and enable external audio or set it to AUTO which detects if the HDMI is active I assume.
I enabled ARC and made sure that I had the best HDMI cable I own in use for the connection but to my disappointment the sound remained out of sync. The Pioneer VSX-21THX documention says nothing about any Audio Return Channel on the HDMI. This AVR predates that apparently.
The next step was to connect the optical audio output of the LG panel back to the AVR. I also made sure that the TV was pushing audio out of the digital optical connection by setting it to use "External Speakers" when I selected the HDMI input. And... BINGO!... synchronized sound!
In order to use the AUTO DELAY or AUDIO SYNC feature which your AVR is likely to have, you MUST insure that you feedback the TV audio to the AVR. It uses this to close the loop and dynamically calculate the required audio delay.
With the LG 84LM9600 this can be either through the ARC function of the #1 HDMI connection or through the optical audio output. I assume that all of the new A/V Receivers will be compatible with this HDMI ARC function. If you have an older AVR with an AUTO DELAY feature then you will need to find another path back.
This appears to be the solution. I am testing it thoroughly by implementing the ultimate jinx and publicly posting it.
It would have saved me hours of frustration if they could have just described this requirement someplace. Hopefully, I can spare you the frustration.