How the hell does HDMI's "Auto Lip Sync" work? - AVS Forum
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post #1 of 9 Old 07-07-2009, 12:03 AM - Thread Starter
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I keep reading how HDMI 1.3b and 1.3c support "auto lip sync correction". I purchased two HDMI 1.3c cables hoping to correct the lip sync issue between my amp and Blu Ray player. It didn't seem to help, but then I set both the receiver and the player at a 30ms delay and everything seemed pretty much in sync. Is this how it works?
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post #2 of 9 Old 07-07-2009, 02:13 AM
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Good question.

I can't give the full answer, I am sorry to say. I believe, at minimum, the TV would need to support HDMI lip sync. Some device has to correct for the problem, and it's not clear to me whether this is the receiver or player - and whether it matters whether the receiver is doing the audio decoding.

Something to know is that HDMI features are often optional, so HDMI 1.3 does not guarantee the feature.

Some info is here -

http://www.abccables.com/info-lip-sync.html

"But this one goes up to 11"
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post #3 of 9 Old 07-07-2009, 07:02 AM
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The display device takes some amount of time to scale, create frames for 120hz, etc. This time is sent back to the AVR and it delays the audio by the same amount. Both the display and the AVR need to support the feature, its not enough to just buy a cable or that the display or AVR are 1.3. HDMI 1.3 does not mean the device supports all features.
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post #4 of 9 Old 07-07-2009, 07:31 AM
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Quote:
Originally Posted by Ghostman84 View Post

I keep reading how HDMI 1.3b and 1.3c support "auto lip sync correction". I purchased two HDMI 1.3c cables hoping to correct the lip sync issue between my amp and Blu Ray player. It didn't seem to help, but then I set both the receiver and the player at a 30ms delay and everything seemed pretty much in sync. Is this how it works?

This is an OPTIONAL feature of HDMI V1.3. Not all HDMI V1.3 devices will support it. It is something that has been way over-hyped.

The way it works is that an earlier device, which handles audio, can inquire of a later device, which DOESN'T handle audio, how much video delay the later device believes it is adding. The earlier device can then also delay the audio that much. Typically the later device is a TV and the earlier device is an Audio Video Receiver (AVR). The expectation is that the AVR is processing the audio, but NOT the video and so can't know how much video delay is being introduced except by asking.

The amount of video delay added by pretty much any TVs is a constant regardless of your settings in the TV or what you are watching. In fact the info returned by the TV when the AVR inquires is almost certainly a fixed number that's just built into its HDMI data block -- without regard to any settings you might have made in the TV. Which means you'd get just as good a result by MANUALLY setting the proper delay in your AVR -- using the simple test found on many calibration DVDs.

The real problem with this "automatic" adjustment is that it does NOT help if some even EARLIER device is screwing up, or if there is an error in the content to begin with. And in reality, these are the bulk of the problems people actually see as lip sync errors.

For example, some cable/satellite providers have been known to send out signals where the video is actually AHEAD of the audio -- i.e., as if they already applied too much audio delay before the signal was sent out. Adding additional audio delay just makes things worse. And there is no mechanism to add VIDEO delay so you are stuck.

In your case the problem appears to be a BUG in your disc player that is generating 60ms of uncorrected video delay. This should not be happening. The player SHOULD be sending out audio and video in sync for all the different types of discs it plays and for all settings.

Again, this is almost certainly a bug in the player. It is almost certainly NOT due to video delay being added by your receiver or TV. So even HDMI V1.3 doesn't anticipate that "automatic" lip-sync correction would handle it. In addition, I don't believe there are ANY HDMI V1.3 players out there which actually implement "automatic" correction -- which would require them to get video delay values from both the receiver and the TV and then add audio delay to their disc playback. This "automatic" stuff, if you find it at all, is almost certainly only going to do anything in AVRs.

And your AVR can't "automatically" correct the problem in the player because there is no way to inquire of an earlier device how much it is screwing things up. And since it's a bug in the player, even if there WAS a way to get that data, the player would probably just provide an incorrect answer!

-----------------------------------

Anyway, you appear to have a 60ms bug in your player. It happens. You are fixing that by adding 30ms delay in the player and an additional 30ms delay in your AVR. That's fine as a workaround SO LONG AS that delay value you have put into your AVR doesn't screw up any OTHER sources you are playing through that AVR, such as your cable/satellite TV.

Also keep in mind that some discs already have screwed up lip sync in the contents coming off the disc. There is no way to automatically correct for that. You have to make MANUAL adjustments disc by disc or just live with the problem on the faulty discs. To test what's really going on in your player you need to use a disc that doesn't have any such problem -- typically a calibration DVD.

The worst case is when the lip sync varies as you play the disc. This too is often due to a bug in the player. Error builds up and gets worse as you continue playing the disc. Often, pausing the disc or a brief reverse will cure the problem -- for a while.

If you conclude your player really is causing this delay, then check for a firmware update for your player.
--Bob

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post #5 of 9 Old 07-07-2009, 07:06 PM - Thread Starter
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Thanks so much. That's all really helpful stuff. I think the 60ms bug may be right because when I watch Blus at 60fps they seem pretty in-sync. it's only when i'm watching at 24fps that I have any noticeable sync issues. I called Sony's tech support (I have A BDP-S350 player) and they said they had never heard of that problem....then proceeded to show me where the A/V Sync adjustment was when a mere two minutes before I told him that I had already adjusted to 30ms delay. Alot of help there. He also suggested I keep the audio output set at 48mhz instead of 98mhz. To my understanding most blu-rays don't even feature 98mhz sound....would that really make a difference?
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post #6 of 9 Old 04-22-2011, 10:32 AM
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Hey guys I'm a relative newby When it comes to this. This is probably my 3rd system buy I consider it my first. I have a samsung un55c8000. Integra dtr 40.2. Bdc6900. Sib xl lcr, sib for Surround and a cub 2 sub all made by focal. Xbox 360 s 250gb and a comcast cable box. I am running everything into receiver thru hdmi except the Xbox to avoid game lag which goes to the tv hdmi and optical to the receiver. My 1st problem is lip sync. Every input is off and I am forced to use the manual av sync to correct it. I would think since all these devices are less than a year old and hdmi 1.4 compliant that I wouldn't have to do this and it would happen automatically. Cable is off about 40 ms and blu rays seem to vary. For instance older movies like the departed had to be cranked up to 250 ms. Tron legacy seemed to be fine. Why are my devices not speaking to each other? My second problem is I was hoping for some heavy bass. I realize only 1 8" inch downward firing sub isn't optimal but it doesn't rumble like it should. I have audyssey multeq set up and have even turned the sub trim level up 2 db after. Should I look into buying another cub 2 to match or I was looking at an hsu 15 inch sub so I can get lower than 40 hz. Any help would be much appreciated. Thanks.
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post #7 of 9 Old 04-22-2011, 11:27 AM
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We have found in many instances the amount of audio delay depends heavily on the source and its A/V stream. Frequently when a HD program is relayed it goes through various uplinks/downlinks which can create latency especially for the HD video.. And it can/will vary significantly between channels and sources..

So be prepared to tweak it as required as 1 setting is not universal..

Just my $0.02...
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post #8 of 9 Old 04-22-2011, 11:29 AM
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It makes me think that auto lip sync is a False claim
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post #9 of 9 Old 05-25-2014, 01:01 PM
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"Automatic lip-sync correction (TM)" Note the Trade Mark! Trade Marks do not have to be "true". "World's Finest Chocolare (TM)" could be the world's finest chocolate but they don't have to prove it since it is a trade mark.

The way the feature is supposed to work - if a TV (sink) supports it - is that the TV during the EDID session (like plug and play for computers) will pass 2 video latency values to the source (AV Receiver). One for progressive and one for interlaced video. It should also pass 2 audio latency values if there is any audio delay already added. The AVR is supposed to subtract the audio latency from video latency for the format being passed (progressive for example) and delay the audio by that difference. So, what Bob said above is 100% correct.

If it worked perfectly as intended it would rarely result in perfect lip-sync since most content is off before the TV gets it.

But the vast majority of TV's I've had do not support it AT ALL. They don't pass any latency values! A Samsung Un55 8000 series was mentioned above. I have the 60" Series 8000 which I feel sure is almost identical and it does NOT supply any latency values. Neither do my 32" Samsungs or my Vizio's. I have an older Toshiba which "does" - so it isn't a matter of whether they are NEW or not. The Toshiba supplies 100 ms for progressive and 116 ms for interlaced but it also supplies identical audio latency values so the net is zero. An AVR receiving those values would not apply any added audio delay because the Toshiba is already delaying the audio. While that "sounds" like a good thing - Toshiba delaying the audio equal to what it thinks the video delay is - it definitely is NOT because Toshiba (on that model) does not allow the user to control that audio delay. It is fixed and can't be turned off (unless via a service menu given only to authorized techs since an error can render the TV irrepairable). It's a bad thing for a manufacturer to do and at least Samsung and Vizio (on the models I have) allow the user to control the delay to their speakers even though they don't support "auto correction". I turn all audio delays OFF on all my equipment and let a dedicated lip-sync correction box solve the problem,

Bob mentioned cases where the audio is already delayed too much (I've even seen DVD's like that) and in those cases you can often correct lip-sync by lowering the audio delay you are adding below what's needed to offset the TV's video delay. In that way you can use the TV's inherent video delay to offset the audio delay. As long as the audio delay in the source signal isn't greater than the TV's video you can. When I encounter arriving audio delay I simply lower the delay (on my Felston DD740) until it's perfect and so far I've never seen arriving audio delay above my TV's video delay. So I can correct up to 100 ms arriving audio delay as well as up to 680 ms video delay regardless of where it comes from. But back when I watched that Toshiba I could not do that since Toshiba had a fixed 100/116 ms delay applied to its speakers. I couldn't correct arriving audio delay at all. Luckily there is usually additional video delay - not audio - in the arriving signals so I am usually adding more audio delay.
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