# Lip sync / audio delay



## alienmuppet

Hi,
I have a Panasonic P42GT50 TV and a Panasonic BDT130 Blu Ray player. My AV receiver is a bit out of date; a NAD T752, so I have to feed it the audio via optical.

I notice lip sync issues sometimes when watching Blu Ray. Does anyone know if the TV tells the Blu Ray player what the delay should be (via HDMI) and the Blu Ray player then delay the audio out sent via optical? I've only heard about the TV telling the AV receiver what the delay should be, and the AV receiver delaying the audio as neccessary, but that obviously won't work in the configuration I'm talking about.

If it does not.. then I guess I have 2 options. Either upgrade my AV receiver to something a lot more up to date (like the later NAD maybe) that has audio delay automatically or manually adjustable, or I buy something that will delay the audio (I've seen a few).

Thoughts?


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## theJman

I don't recall ever seeing a TV with that ability. AV receivers yes, even some blu-ray players, but not the TV itself. Generally speaking, they aren't very "intelligent" devices - most of the logic and functionality of a HT system is in the receiver and/or player.


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## tonyvdb

Agreed ^^
its going to be a bit of trial and error to set the delay in the receiver or Bluray player but this delay can be caused by many different things including length of cable, number of devices the signal goes through and if you use some sort or frame creation/refresh rate increase in the display.


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## alienmuppet

I thought the idea though was that the TV told the AV receiver what the delay should be? If not, what does the HDMI lip sync do?


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## theJman

The TV is a passive device, with few abilities of it's own. Think along the lines of a speaker; without the amp sending a powered signal they really aren't able to do a whole lot. Same general concept with a TV.

The Lip Sync functionality sets a very small delay in the audio stream to compensate for the fact that the audio may be going through a "longer" or more elaborate (read: slower) signal chain than the video is, and therefore the timing of the two signals becomes different. The TV has no idea whatsoever that this is occurring though, and neither do any of the other devices for that matter. The setting is completely manual, and as tonyvdb states, is a trial-and-error adjustment.


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## alienmuppet

Thanks - I do understand all that, I'm a software engineer with a strong micro-electronics background, and a background in making devices talk and designing protocols to make them talk. However I have not spent much time researching HDMI and am new to it, I had a CRT up until recently.

I had read that the HDMI 1.3 standard (possibly 1.2a onwards) allowed devices during the HDMI handshake to pass delay information (that is a mixture of researched and gleaned information from forums, hence I came here to try and clarify and find out about if people knew the general norm).

Also in this case, it is the audio that is being delivered too fast, as the TV is processing the picture and likely causing a delay of over 60ms. The audio has a small delay due to the processing in the AV receiver, though I doubt it is up there with the picture processing delay.

I do not agree that A TV is a passive device like a speaker; it has a computer inside and it does exchange information with the HDMI device it is linked to. If I turn the TV off, my Blu Ray player knows this and will turn off too. In the other direction, the TV obviously knows the kind of signal it is receiving from the Blu Ray player.

How sophisticated this communication is in either direction I'm not sure, hence the question. I can't see any reason why a TV could not tell a device the processing time on initial HDMI handshake, so I wondered if this was the case.


Thanks for your replies so far


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## RBTO

The video processing by far takes longer than any audio processing and as far as I know, there is no delay reporting going on with HDMI other than possibly a handshake telling the display that the connection is HDMI (which has a short delay of its own) rather than analog. There is some reporting going on with HDMI, but I don't believe that applies to audio delay (Panasonic has VieraLink which can sync up the turn-on/off of Panasonic devices connected via HDMI - no audio syncing though). I have a Blu-Ray player which feeds my audio system via an analog path. I can send the video by analog (component) or HDMI and see no difference in lip sync, but that's my video display which has insignificant latency. I've heard stories of certain brands having noticeable processing latency but I've yet to run into it with my displays (a Panny projector and LED/LCD flat screen).

As was mentioned previously, "smooth motion" processing can be a culprit, but I always turn it off since it bothers me to no end. I would suggest you try disabling it in your display to see if it matters.


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## theJman

alienmuppet said:


> I do not agree that A TV is *not* a passive device like a speaker; it has a computer inside and it does exchange information with the HDMI device it is linked to. If I turn the TV off, my Blu Ray player knows this and will turn off too. In the other direction, the TV obviously knows the kind of signal it is receiving from the Blu Ray player.


I doubt you meant to put that 'not' in there, otherwise your double negative essentially means you're agreeing with me. 

If you'll note I said "Same _general_ concept with a TV" - I wasn't intimate they were identical. Obviously there are differences, but the bottom line is a TV and a speaker are far more similar than dissimilar; they both need something to give them signal, and tell them what to do and how to go about doing it. That's the only point I was making with my analogy.


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## alienmuppet

theJman said:


> I doubt you meant to put that 'not' in there, otherwise your double negative essentially means you're agreeing with me.


Yes, sorry, corrected!


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## tonyvdb

RBTO said:


> The video processing by far takes longer than any audio processing.


This really is the bottom line, as you add more processing to the video you introduce delay. Audio is much easier to process and at this point no TVs have the ability to correct this due to the fact that it has no way of knowing how many other devices are in the chain that have altered the signal


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## RBTO

tonyvdb said:


> This really is the bottom line, as you add more processing to the video you introduce delay. Audio is much easier to process and at this point no TVs have the ability to correct this due to the fact that it has no way of knowing how many other devices are in the chain that have altered the signal


Right, and there really aren't any cues in the audio which would allow auto syncing. How's the TV to know if the lip sync is off at all, much less by how much?


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## alienmuppet

tonyvdb said:


> This really is the bottom line, as you add more processing to the video you introduce delay. Audio is much easier to process and at this point no TVs have the ability to correct this due to the fact that it has no way of knowing how many other devices are in the chain that have altered the signal


I would bet that some TVs would delay the audio coming out of its own speakers to be in sync with the picture. If a TV knows that it spends 40ms processing the picture, there's no reason it cannot delay the audio for 40ms. The processing would not even be variable; it couldn't be because otherwise the frame-rate would not be smooth.

It seems a fairly simple idea that the TV could share this latency with say, an AV receiver so it knew how much to delay the audio automatically. The delay does not change, so it would only need to inform the device on handshake, or when the picture mode changed.

Here are some links I found on the subject:

http://www.allquests.com/question/2406237/Does-HDMI-13-fix-lip-sync-issues.html

http://www.octavainc.com/HDMI%201.3.htm

On the last link, see the bit titled "Lip Synch Correction".


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## tonyvdb

I can assure you that there is no feature that automatically corrects this audio or video delay. It has to be done manually.


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## alienmuppet

tonyvdb said:


> I can assure you that there is no feature that automatically corrects this audio or video delay. It has to be done manually.


Fair enough :blink: I'm confused at to why there is a lot of talk about it with the HDMI 1.3 standard :huh:


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## bonusbartus

tonyvdb said:


> This really is the bottom line, as you add more processing to the video you introduce delay. Audio is much easier to process and at this point no TVs have the ability to correct this due to the fact that it has no way of knowing how many other devices are in the chain that have altered the signal


I'm not sure if this is entirely correct, the TV could know how big the delay is between receiving its content and displaying it. Besides, my Philips PFL7606 from 2011, does have a HDMI audio delay setting....


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## RBTO

bonusbartus said:


> I'm not sure if this is entirely correct, the TV could know how big the delay is between receiving its content and displaying it. Besides, my Philips PFL7606 from 2011, does have a HDMI audio delay setting....


No argument about a TV knowing its _own _delay factors and compensating for them - most all do that. It's _other_ devices which might exist in the HDMI path (i.e., an AVR) which also contribute to processing delays that the TV could not be aware of, unless those devices transmit their delay factors to the TV (which at present _*isn't *_the case), so the bottom line is that any adjustments for overall system latencies _must_ be done manually (hence the _manual_ adjustment on your Philips).


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## bonusbartus

RBTO said:


> No argument about a TV knowing its _own _delay factors and compensating for them - most all do that. It's _other_ devices which might exist in the HDMI path (i.e., an AVR) which also contribute to processing delays that the TV could not be aware of, unless those devices transmit their delay factors to the TV (which at present _*isn't *_the case), so the bottom line is that any adjustments for overall system latencies _must_ be done manually (hence the _manual_ adjustment on your Philips).


No, it is not manual adjustment, its a called delay audio output (translated from dutch) but I guess it could also be used to delay only the audio going from tv over the HDMI back to AVR, and not send info on received content


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## RBTO

bonusbartus said:


> No, it is not manual adjustment, its a called delay audio output (translated from dutch) but I guess it could also be used to delay only the audio going from tv over the HDMI back to AVR, and not send info on received content


Is that on OFF/ON option then? I believe the feature you're talking about relates to the ARC feature (audio return channel) of the HDMI. ARC allows audio recovered by the TV (say an off-air channel audio) to be sent to an AVR using the HDMI connection.


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## bonusbartus

Yes I think you are right...

so on the manual settings...
I have my htpc->HDMI1_RX-V667-HDMIMONITOR->TV
I can give an offset in the yamaha for the lipsync's auto setting, or put it on manual.
sometimes it seems like it is ok, but a lot of times I get the feeling it is off...
It might have something to do with different audio formats (DTS/DD vs PCM)
any good/accurate/easy ways to set this up/calibrate/test this right?


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