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


Sound out of sync with the picture on your TV or projector? Voice doesn't match lip movement? Lip-sync error or "av sync error", plagues most TV's and projectors. Especially HDMI plasma, LCD, and DLP displays with larger 4K and 8K screens.  But what causes it and why do all the recommendations on how to correct it fail?

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

"delay of video allowing sound to be heard 'before' the action which produced it is seen"

The only way to fix it is to delay the sound to match the delayed video. Most TV and AV receivers offer a "fixed" audio delay  - often in a menu that's impractical to adjust while watching and usually offering adjustment in HUGE increments of 10 or even 20 ms!


But the main reason all the recommendations fail is that a fixed delay can't compensate for the changing video delay.

To really achieve perfect lip-sync error correction you need to be able to adjust sound delay while watching in 1 ms steps whenever the video delay changes. 1/3 ms is even better for the most sensitive but the main requirement is to be able to change the audio delay since video delay often changes between sources and even programs on the same source.


Since HDMI carries both video and audio as an HDCP encrypted signal you first need access to the digital audio so you can delay it. Most STB's and TV's have optical (Toslink) or coax digital outputs. You will continue to use HDMI for the video going to the TV or projector since it  will deliver 4K and 8K images

But why is it so important to align audio with video? (Especially if you aren't very sensitive to lip-sync error.)

Sound "before" the action that creates it can never occur in nature and is therefore very disturbing when our 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. Force yourself to focus on the lips and you will probably be surprised.

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. Even when we do it subliminally.

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"!

With the DD740 you can easily align sound and picture 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 in 4K or 8K resolution - 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.  We call the value at which it is noticed consciously their "threshold of recognition" and it varies enormously from person to person depending upon the individual's defense mechanism - how far he can look away from the moving lips so as to ignore the lip-sync error.

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.

If you aren't very sensitive to lip-sync error a TV's 20 ms fixed audio delay might make it tolerable but our DD740 allows perfect correction (within 1/3 ms) while watching which will satisfy the most sensitive among us while restoring reality.


 Here's our "great" solution:

The Felston DD740  digital audio delay solves lip-sync error by letting you delay audio in 1 ms  (or 1/3 ms in fine mode) steps to compensate for the cumulative video delays - no matter what their cause - at the touch of a button on its remote while watching TV.

The DD740 connects between up to four digital audio sources and your AV receiver (or Sound -Bar) allowing you to delay the audio to match the video achieving "perfect lip-sync".  Because lip-sync error changes between sources and even between programs on the same source the DD740's hand held remote is an essential part of true lip-sync error correction. It allows moving the audio back and forth at the touch of a button without any disturbance in the video

To buy the DD740 click the link to PayPal below. Our products are also on Amazon and eBay at slightly higher prices.(eBay because they offer an international shipping program beneficial to our foreign customers.)