The solution guaranteed to correct "lip-sync":

 

Before we address how to correct lip-sync error let's explain why it is so easily misunderstood:  Many "experts" - even video editors - have believed the fact that video is comprised of discrete frames meant the sound accompanying each frame was in alignment if it fell anywhere in that frame's 33 to 40 ms duration. They overlooked the reason motion pictures work in the first place! "The fact that repeated static frames create the perception of continuous motion in our brain.  Sound needs to align with that "perception" just as it does in the real world!"

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With a DD740 you can "see" this transformation from being out of sync as you add delay in small increments of 1 ms (or even 1/3 ms)  to being in perfect sync when sound aligns with video.  If you know this is what you need skip to our BUY Now link at the bottom of this page. If not, read on: We'll probably tell you more than you want to know about lip-sync correction.

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Many people are confused by HDMI's "automatic lip-sync correction" claim and think it can solve this problem. It can't and only allows a TV to request a "fixed" delay which is set for that particular TV and has nothing to do with the actual lip-sync error present in the signal. It won't correct lip-sync error any better than any other fixed delay and often makes it worse!

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Furthermore, many TV's (most Sony, Panasonic and Toshiba TV's for example) delay audio in their HDMI input and don't allow a user to stop it. Intercepting digital audio before a TV is allowed to touch it is the only way to completly correct lip-sync on those TV's. Samsung, Vizio. etc. usually allow turning any audio delay OFF but don't accept Dolby Digital in their HDMI inputs so intercepting audio is the only way to get Dolby Digital from HDMI inputs on those TV's. The DD740 supports both digital audio formats (optical and coax digital) and automatically converts between them.

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Our HD940 is the only HDMI lip-sync corrector ever developed as far we know.  After building  300 of them we stopped production and never released it.  For more info on "why" see our Digital Audio Delay page under "Using HDMI".  HDMI is great for video but not for synchronized audio.

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There is no way to automatically correct lip-sync because there is nothing to define when video and audio are in sync. From content creation until delivery by your large screen there are many places along the broadcast chain where audio video sync error - lip-sync error - creeps in.  An audio delay must be adjusted while viewing the out of sync video to offset the cumulative lip-sync error.

 

When sound is out of sync with the picture on your TV and voice does not match lip movement you have begun to notice lip-sync error or av sync error.  It plagues all TV's and projectors and is worse on larger 4K and 8K screens which is probably why you have just noticed it.

 

Lip-sync error causes audio to be heard "before" the action which produced it is seen. You hear speech before you see the lip movement that produced it. That's impossible in the real world but not on your TV!

 

If you have tried adjusting a fixed audio delay to correct  lip-sync you have already discovered it's impossible. A variable delay is required.  

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To achieve perfect lip-sync error correction you need to adjust sound delay in small steps when the video delay changes. 1 ms usually works well and 1/3 ms is even better for the most sensitive but the main requirement is to be able to change the audio delay in small steps without upsetting the image as you watch.  Pressing the DD740's + and - buttons accomplishes that.  Its numeric pad can be used for large delay changes.

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Most TV's, projectors and STB's provide a digital audio output - usually Toslink optical - which the DD740 will delay before it goes to your sound system. The DD740 will also delay coax digital audio but that's used less often.

 

The DD740 features "bit-perfect" reproduction so its digital output is identical to its digital input eliminating any chance of degradation.

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Synchronizing audio with video is important even if lip-sync error doesn't consciously bother you:

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You want a realistic home theater, right?  You've spent a lot and may feel you've achieved it  but the "image" is not all that matters when creating an immersive environment.

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Sound "before" the action that creates the sound  is impossible  in the  real world. Our brain can't reconcile this conflicting visual and aural information.

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There is strong evidence based on research done at Stanford that our subliminal defense mechanism to this impossibility is to look away from the faces and moving lips so as not to notice this contradiction of reality. Force yourself to focus on the lips in a "talking head" scene and you will probably be amazed at the error you have been able to ignore by subconsciously looking away.

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Just as we have less trust for those who do not make eye contact we get that same negative impression when "we" are the ones looking away from the characters faces. Even when we do it subliminally.

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To read the actual research report from Stanford that statistically proved lip-sync error interferes with viewer perception causing content to be less believable click HERE.  It's a PDF report you can save. Note that their results were the same whether viewers consciously noticed the lip-sync error or not. 

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If you think the industry should have solved this we agree and SMPTE has a solution but Tektronix's AVDC100  could have solved it almost 20 years ago.  The Stanford research has been known for over 28 years and still no solution. Why? Because it is a "chicken or the egg" problem. The audio and video must be synchronized at content creation and however it is marked (meta data in the current proposal) must be maintained throughout the entire broadcast chain to be used to restore sync. No one entity wants to invest in the required equipment until "everyone" has plus it won't solve the problem for any preexisting content.

 

So, lip-sync error is not just an annoying distraction noticed by some of us but it fundamentally disrupts the immersive home theater environment even when viewers aren't consciously aware of it.  It's ironic that these almost perfect 4K and 8K displays  demand such a large amount of data increasing the video delay which allows the sound to arrive even earlier and creates the most unrealistic spot on the planet - a place where sound comes before the action that created it!  The silver lining is that you can fix it.

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Correcting lip-sync error "restores reality"!

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With the DD740 you can easily align sound and picture and realize the realistic environment you've already spent so much to achieve.