View Full Version : Audio/Video Sync with Dolby Digital
10-14-2005, 10:30 PM
I seem to have the opposite problem from most people....
When I turn on Dolby Digital on my HDTivo, I get a sync problem where the video is ahead of the audio (so I see the lips moving before I hear the words). Most "fixes" for this issue seem to be aimed at delaying the audio, which in my case, would simply make matters worse.
Is there any fix for this kind of problem? My video comes straight into to the TV while the audio is sent directly to a receiver. Because of the way I'm set up (my HDTivo is in a different room from the HDTV, I have to use a device to turn the optical digital audio to coaxial, and a device to send component video and digital audio over CAT5 (1080i-dot-html at the svideo-dot-com website). Are these devices causing my problem? Is there any way to delay the video to compensate?
10-15-2005, 12:56 AM
Ok, more information:
I hooked up the HD Tivo to another receiver that I have that is co-located, and everything works fine with DD. So it must be my optical-to-coaxial digital audio converter that is adding in the delay.
Does anyone know of a device that can convert optical digital audio to coaxial digital audio without introducing a significant delay? The HD Tivo is not co-located with the HDTV (and I need it that way), and I have no way of feeding an optical cable the 30+ feet between them. Since the HDTivo has only an optical output (what the hell is the problem with providing a reasonable number of outputs???!!!), what else can I do?????
P.S. I used the digital audio out (set to dolby digital) on my old Tivo with no problems. I also have no problem with this setup when the HDTivo is set to standard audio output (with non-DD audio still sent over the optical-converted-to-coaxial setup).
10-15-2005, 07:04 AM
The problem that you have that is common to everyone elses is starting new threads about the same issue. :rolleyes:
10-15-2005, 09:42 AM
Billy66, that's not the least bit useful. All of the other threads I've found are about the audio being ahead of the video -- hence people discuss options for delaying the audio to compensate (using audio delay in their receiver, the "lipfix" device, etc). In my case, it's the opposite. The video is ahead of the audio. I need to know if there is any similar device for me to delay the video so the audio can catch up, or a device which does the optical-to-coaxial conversion without introducing so much delay.
Again, my problem is not with the source. When I hook up to my projector, and the sound processor in the wiring closet where the TV is (where I can use a straight optical connection without the optical-to-coaxial conversion), everything works fine! It's only when I do the o2c conversion that I get a problem.
So please, refrain from your nasty comments.
10-15-2005, 12:41 PM
How much are you willing to spend? Video delay processors are currently very expensive, although I did find this link using Google that promises something cheaper in the future ....
10-17-2005, 03:53 PM
I have used my DVD recorder to delay the audio (I know this is not your problem, stay with me tho) and listen to the delayed audio with undelayed video, to sync up the two. The delay is about two to 2.5 frames. If you have a DVD recorder at you "alternate location" maybe you could view the DVD-R delayed video and listen to the "slowed due to O2C conversion" delayed audio, and they would sync up. I hope that makes sense.
Another posibility is change the output resolution of the HD-Tivo, so that there is one extra conversion in the chain. You probably tried this already. On my TV, 1080i and 720p out of the tivo ususally look very similar in quality. YMMV.
10-17-2005, 06:56 PM
... All of the other threads I've found are about the audio being ahead of the video -- hence people discuss options for delaying the audio to compensate (using audio delay in their receiver, the "lipfix" device, etc). In my case, it's the opposite. The video is ahead of the audio...
You are right to make that distinction. Most broadcast and transmission problems cause audio to lead video. DD in consumer gear is one place where the opposite happens. Short of a time machine, you need a way to delay the video. DVDRs work, but there aren't any HD-DVDR's available yet, and won't be for a long, long time.
01-26-2006, 11:59 PM
Are you determining that video leads audio subjectively (visually)? I ask because an optical to coax converter will not delay the s/pdif signal. It is simply a Toslink optical receiver and perhaps an output transformer for the coax output. If you video is indeed ahead of your audio it won't be due to that converter.
It is VERY difficult to look at lips moving and tell whether audio leads or lags. It is eaier with a musical performance especially one with occasional percussion not spaced closely.
Syncheck makes a device to actually measure this by playing their test DVD and using the instrument to measure what it SEES. It's $290, however plus $20 for the DVD. Good for stores maybe.
I'd suggest getting a Felston DD540 from LipFix Technology for $230 and trying it - an audio delay. If your problem actually is a video signal ahead of the audio you are right that it won't help but you will at least have confirmed it and they offer 100% money back return for 14 days so it won't cost you anything to find out. My guess is that you will discover it is really a video delay that just looks like an audio delay (since I have never seen a consistent audio delay in any equipment that wasn't designed to specifically delay audio). For a measureable audio delay to occur the audio must be stored in memory and read back later. Unless the TIVO gets confused and plays its audio track behind its video there is nowhere for the audio to get delayed. It could happen if a broadcaster overcorrects but I have only seen that once.
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