I am with a company which manufactures products to correct lip-sync error in home cinema systems (which I won't name so this is not promotion) and I'd like to mention a few facts about lip-sync error that are not intuitatively obvious which make discussions on forums somewhat difficult:
1. Lip-sync error of some magnitude is essentially always present in every broadcast and even encoded into many DVD and BluRay discs.
2. Lip-sync error is "impossible" in the real world and when we are confronted with this contradition of reality on screen we subliminally avoid noticing it by perhaps looking away from the offending lips and faces of the characters or perhaps defocusig and this defense mechanism allows most viewers to ignore very large lip-sync error often in the 40 to 80 ms range.
3.Once a viewer's "threshold of recognition" - say 80 ms for example - is exceeded (He can no longer look askanse enough to ignore it and it enters his conscious mind.) he begins to focus on the lips and can detect much smaller lip-sync error than before. His NEW "threshold of recognition" can be as low a a milli second in some cases.
4.Lip-sync error in broadcasts and in media like DVD and BluRay discs varies from programme to programme and from disc to disc and is largely ignored by the industry which focuses on the "fixed" lip-sync error caused when a display delays video more than audio. Most TV's nowadays add audio delay to its speakers equal to its video delay but even that's usually off a little since the video dealy will vary depending upon the format being sent to the TV.
5. HDMI 1.3 and above has an "auto lip-sync correction" feature which is widely misunderstood: Most consumers think it automatcally corrects the changing lip-sync error in the signal but it doesn't. It only allows a TV (the SINK) to tell its SOURCE the video delay it will add for progressive and interlaced formats (ignooring resolution and frame rate differences) and only those 2 FIXED delays (about 16 to 20 ms different) will be added (if the TV and source support the feature). That will come close to offsetting the fixed error caused by TV video delay but does nothing to correct the other lip-sync error already in the source signals. But it might get it close enough to be "masked" by the viewer's threshold of recognition.
6. About 20 years ago research at Stanford University in the US showed most viewers don't consciously notice lip-sync errro below 42 ms ( a PAL frame is 40 ms) but even when not noticed it still caused the negative impact on viewer perception their reserach statistically documented. The negative feelings about the charactrs they documented when lip-sync error was off were the same kinds of feelings we have about those who do not make eye contact with us but ironically it seems to be the "viewer" who is not making eye contact with the characters as he tries to avoid the impossibility of the lip-sync error confronting him.
Now for how this all applies to forum discussions:
Most discussion on forums about lip-sync error focus on "equipment" as the primary cause but often it isn't the equipment. When equipment causes a lip-sync error it is usually a FIXED error not changing over time and a fixed audio delay like most AV receivers and some TV's offer can correct it.
The problem is that once you notice lip-sync error and even aftre correcting the "fixed" error that may have pushed this into your consciousness your new "threshold of recognition" is so much smaller you then notice the changing lip-sync errro in the broadcasts. The only way to cancel those lip-sync errors that change from programme to programm is to adjust an audio delay while focusing on the lips during that particular programme.
This also means that one forum member who says his idetical equipment has no lip-sync error while another member is going crazy could be seeing the same thing but one has an intact defense mechanism and doesn't realize he is subliminally loking away from the characters faces. Almost everyone sees lip-sync error if they focus intently on the lips and that's what you have to do while adjusting the audio delay if you really want it perfect.
But many viewers don't worry about the negative impact as long as they don't consciously notice the problem even though the research at Stanford showed it is still there at 42 ms
Do a Google search for lip-sync error and you will find a lot of information on the subject. If your are interested in the Stanford research the authors of the paper were " Byron Reeves & David Voelke".
As you participate in forums keep in mind what one member "sees" isn't necessarily perceived the same way by another member and be aware that your own sensitivity to lip-sync error will change once you deliberately focus on the lips.
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