What causes "lip-sync error" and how can I fix it?


Lip-sync error, sometimes called "lip-flap" or "av sync error", plagues most TV's. For plasma, LCD, and DLP displays with larger HD and 4K UHD screens the problem is even worse, but what causes it?

There are many causes (see Technical Details ) but most boil down to:

"delay of video more than audio allows speech to be heard 'before' the lip movement which produced it is seen"

Sound "before" the action that produces it can never occur in nature and is therefore very disturbing when the brain tries to process this conflicting and impossible visual and aural information.

There is strong evidence that our subliminal defense mechanism is to look away from the faces with moving lips so as not to be confronted by this impossibility.

But just as we have less trust for those who do not make eye contact we get that same negative impression when we are looking away from the characters faces.

To read the actual research report from Stanford that statistically proved lip-sync error interferes with viewer perception causing presentations to be less believable please visit our "Technical Details" page where you can download the PDF. Note that their results were the same whether viewers consciously noticed the lip-sync error or not. 

So, lip-sync error is not just an annoying distraction noticed only by a few but it fundamentally disrupts the immersive home cinema environment even when viewers aren't consciously aware of it.

Correcting lip-sync error "restores reality"!

Now that you are aware of the lip-sync error in your system you can easily correct it and realize the realistic environment you've already spent so much to achieve.

At InfoComm we demonstrated the contradiction of reality - "sound before the action that produced it" - called lip-sync error - which undermines viewer perception in home  theater systems.  Ironically the quest for realism - for the perfect image - creates the most unrealistic spot on the planet - a place where sound can occur before the action that produced it!

The only way to correct lip-sync error caused by delayed video is to delay audio an equal amount.

Most people initially only notice lip-sync error when it exceeds 40 to 75 ms but this varies enormously and really depends upon the individual's defense mechanism - how far he can look away from the moving lips so as to ignore the increasing lip-sync error.  We call the value at which it is noticed consciously their "threshold of recognition". 

An individual's "threshold of recognition" falls greatly once it has been reached and lip-sync error has been noticed.  At that point their defense mechanism can no longer compensate and the sync problem enters their conscious mind.  The same person who was never bothered by a 40 ms lip-sync error may, after noticing 120 ms error, become far more sensitive and notice errors only a small fraction of their previous "threshold".   Many people can "see" lip-sync errors as small as "one milli-second" and some can even detect 1/3 ms errors.


 But finally there is a "great" solution:


The Felston DD740  digital audio delay solves lip-sync error by letting you add an audio delay to compensate for all the cumulative video delays - no matter what their cause - at the touch of a button on its remote.

It connects between four digital audio sources and your AV receiver (or digital speaker system) allowing you to delay the audio to match the video achieving "perfect lip-sync".