|What they discovered at Stanford: |
Click HERE to read the full research report and see how this contradiction of reality undermines our perception even when we don't notice the problem. Note on page 4 how viewers described the characters when audio and video were out of sync as: 'less interesting, more unpleasant, less influential, more agitated, less successful' - the same way we often feel about people who don't 'look us in the eye'. Also note most viewers can ignore 2½ video fields of error (41.25 ms) but still suffer its negative impact.
What can explain this negative impact on our perception?
In the real world you can't hear a sound before you see the action that created it. To the contrary, you will see the action - lip movement for example - and the sound will follow, delayed 1 millisecond for every 13 inches it travels.Home theaters violate this physical relationship when delays from video and audio processing allow sound to arrive too soon or too late. Since we can't reconcile this physical impossibility, we avoid it, subliminally looking away from the characters' lips and faces. This hides the problem but causes the negative impression just as if the characters were the ones 'not looking us in the eye'.
Don't most A/V receivers claim to correct A/V sync?
Most can add a fixed audio delay to offset the fixed video delay caused by your display but that doesn't correct the sync error already in your broadcast or DVD sources. A/V sync can vary more between programs and DVD's than the 41.25 ms Stanford proved still undermines our perception.
Why doesn't HDMI 1.3 fix this?
The widely misunderstood 'automatic lip-sync correction' feature of HDMI 1.3 does nothing more than 'automatically' set the same fixed delay most receivers set manually. It does nothing to correct a/v sync error already in broadcasts or DVD's. Ironically, it can make lip-sync error 'worse' when audio arrives delayed.
How can an audio delay correct audio that's already delayed?
Alone it couldn't but with your display's inherent video delay it can. You simply reduce it below what's needed to cancel your display's video delay and you have an adjustable video delay to correct for delayed audio which is more common in DVD's.
The only way to correct lip-sync error and eliminate its disruption is to fine tune a variable delay while watching each source.
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|Unlike your A/V receiver's audio delay, the DD740 is designed for easy on-the-fly adjustment while viewing with no image disturbance. This makes fine tuning for perfect lip-sync practical as it changes between programs or DVD's, and the DD740's 680 ms delay corrects larger lip-sync errors common in HDTV.|
|Conduct your own test:|
We avoid this contradicton of reality by subconsciously looking away. To prove this, force yourself to "focus on the lips". You'll be amazed at the lip-sync error you've been avoiding and see why it's so disruptive.
|Felston Audio Synchonizer |