Almost anyone with a digital projector, LCD TV, or plasma TV will notice that the picture and the sound are not always in synch. This becomes most apparent in close-ups when lips do not move in exact time with the sound. This phenomenon is particularly common if you are sending the video signal to a display device, and the audio signal to a separate AV receiver. The reason it happens is simple: There is much less digital processing required to deliver an audio signal to a speaker than there is to deliver a video image to a screen. So the sound often gets to your ears before the picture gets to your eyes.
When audio arrives slightly ahead of video, it is annoying to say the least. It creates a sense of unreality that limits your ability to immerse yourself in the material. The human mind can accept video ahead of audio, since that happens in the real world all the time-you see the lightening before you hear the thunder. But when sound arrives before you see the event that caused it, the brain gets confused. Instead of concentrating entirely on the drama at hand, you are subliminally aware of the fact that the lips are not moving in time with the sound track.
When this happens you get distracted. You try to figure out if it's a chronic problem or a temporary aberration. You wonder whether you will notice it again in the next scene as much as you did in the previous one. This semi-conscious brain chatter is going on while you are trying to concentrate on the movie. So your ability to enjoy the big screen home theater experience is short-circuited, quite often without you even being aware of it. When audio and video are not in perfect synch, the whole experience is less "real" and believable.
The solution is to introduce an audio delay into the system. You might already have an audio delay feature on your AV receiver or external video processor. This can address the problem to some degree, but often not with the precision you really need. A more comprehensive solution is available with the use of the Felston DD740 Audio Delay. It is a little component selling (at the moment) for an introductory price of just $199, and it's a great way to get lip synch problems eliminated from your home theater.
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