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Lip Sync: Getting Sound to Match the Picture
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June 2008      back to HDTV index

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Does it drive you crazy when people's lips don't match what they're saying? It drives my wife up the wall.

This has been a huge problem in television for many years. The entire TV industry can't figure it out, so you can't fix it at home. Don't adjust your sets; it's a problem with the broadcasters, satellite and cable. Again, watch any format of DVD and there isn't any problem.

This problem is worse today than the old days because of digital. In production and transmission, picture and sound travel separate paths. The processing delay for video is often much longer than the relatively simple processing for audio, so video tends to lag audio.

This was never much of a problem in the old days, because these delays didn't vary. One simply added an audio delay to match the video delay, and it was fixed.

Digital production and transmission gear today is wicked because it can have different delays every time it's turned on. When NBC did the 2002 Winter Olympics in HD, every morning they turned on all the gear, and they'd see if they got delays which they could correct. If not, they turned everything off and back on to try again.

If you think its tough getting the lips to match just shooting a show, imagine how impossible it is to get the audio and video to stay synced as programs travel different paths around the world, and then in your local TV station, and then in your cable company and eventually to you.

My wife thought our TV was broken. I assured her it's what's being sent to it. She calls the cable company, and the guy explained to her that they simply had no idea how to fix the problem, and that it's getting worse.

Flat panels don't help, either. Just as in program production, audio and video go through different paths inside your HDTV set. The video signal goes through a lot more processing in a digital set, and some sets can have much longer video delays than others. Most sets are smart enough to have the audio delayed to match the picture. If not, an external audio delay line can get sound to match picture. Heck, if your wife hates the errors on cable, use a delay line and let her adjust it herself!

For fun, look at all the screens in the store playing the same source. When the scene changes, not all the screens change at once. If you turn up each set's volume, unlike in analog days, you'll have a cacophony of unsynchronized audio. Gone are the days when everyone in my college dorm could tune in the same station and blare our stereos together. Since most HDTVs have equal audio and video delays, this isn't a problem for watching just one; but don't expect different models to synchronize with each other.

But hold on - what if you send your audio not through the set, but to a separate amp with no delay? Good luck!

Tektronix invented a genius solution, the AVDC-100 (audio-video delay corrector), that actually listened to the sound and video, and magically encoded the video with the sync information. The same unit could look at the video and sound anyplace else, measure the error, and correct it, on a continuous and automatic basis! It really worked.

You all know the problem I'm talking about, but when we at Tektronix presented this to the industry, everyone in the chain blamed the problem on someone else. No one wanted to use it, because everyone knew the problem wasn't with them. It was a chicken and egg proposition: no one wanted to buy them to produce shows if no one else had them to decode, and no one wanted to buy them to decode the shows that came in if no shows used them.

Sony would have given half of them away to seed the market, but not Tek.

So stop watching lips, or put on a DVD, and be happy. The problem isn't going away.



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