Lip-Sync, Understand and Measuring (1 Viewer)

[Guilo]

Hi all,

I'm a new comer here. I know for sure lip-sync issues are the subject of plenty of topics in this forum. But after reading plenty of literature on this matter over the internet, I am still having questions.

Long story short: I have an A/V setup on which I noticed some minor audio lag. I came up with ways to actually measure it and wanted to check with experts if what I experience is expected or not. Most topics around lip-sync I have read revolve around the video being late because of added video processing in the chain. My observations are the opposite: I have audio being late and no good way to fix this.

The Setup:
AVR: Yamaha RX-1080A
Source: Panasonic DP-UB9000
Display: Epson EH-TW7100
All connected through the same HDMI 2.1 cables

The Test:
I am playing an A/V pattern coming from Spears & Munsil UHD HDR Benchmark. It has a moving bar and a bip signal. It is a 4K HEVC video at 23.97fps. The test has 2 audio tracks, one in Dolby TRUEHD, one in DTS HD-MA
I record the video projected with a GoPro Hero7 Black at 240fps.
The I load this video on my computer and try to see if there is a lag between audio and video.

Observations:
- Audio is late by an average of 12 ms on the DTS track. Audio is late by an average of 40ms on the Dolby track. It doesn't matter whether the player is passing audio through or is decoding audio and sending PCM.
- Audio is perfectly in sync when bypassing the AVR and plugging the UHD player directly into the video projector, leading to think the AVR is the issue
- Setting the AVR in Pure Direct mode doesn't help. I also performed the test with headphones to eliminate any lag introduced by speakers distance. LipSync feature on AVR is disabled, video processing is disabled.


Questions:
- Are there any obvious flaws in my testing procedure?
- Is a 12ms delay expected for an AVR?
- Is it expected for Dolby TrueHD to take longer to decode? How are we supposed to compensate?
- LipSync features found everywhere always allow to delay the audio to match processed video lag. How come there are no ways to add a negative audio delay to catch the opposite issue ?
- I tried to turn on video processing in the AVR in the hope it would actually delay the video and maybe have both in sync as they both would be handled by the AVR but found no conclusive improvement.

Thanks a lot for reading this long post, sorry if some of these questions are obvious.

 

[JohnRice]

Just to explain one thing. There can't be a "negative" lip sync, because the audio can't be before it is, if that makes sense. You'd have to delay the video instead, which would essentially have the same result. Lip sync can be a mysterious thing. I don't have any solutions yet.

 

[JohnRice]

Just give this a try to see what happens. Run everything through the receiver, and turn auto lip sync on. See what happens.

 

[Guilo]

No visible difference with lipsync auto