My photo
Fuquay Varina, North Carolina, United States
A guy finding out if life really does begin at 50.

Friday, December 3, 2010

Getting things in sync

You may not know it but over the last few weeks I've been sorting out my HD and surround sound setup. Basically I had cables all over the place since I got that new HD TV in June. It's now nice and neat and everything is hooked up.

But I now have a BIG issue with lip sync when I use the surround sound (digital 5.1). There has always been a slight lip sync issue, but inserting the Google TV box between the Satellite receiver and the the TV made it way noticeable (worse).

The 5.1 audio signal from the Satellite receiver uses fiber optic cable to connect to the Surround sound with the 5.1 decoder. Next the decoded signals are amplified and sent to the various speakers. That decode does not take long. My guess is a millisecond.

But for the video the path is not so direct. The HDMI cable runs from the Satellite receiver to the Google TV box. The Google TV box de-interlaces the 1024i and rescans that to 1024p and sends that video to the TV using second HDMI cable. The TV then decodes the video again and displays it. It takes 1/15th of a second (2 1/30th second frames) to rescan 1024i to 1024p and it takes another 1/30th of a second to display a frame on so that's at least 1/10th of a second (100 millisecond) delay in the 'picture' relative to the audio. When viewing actors on screen I hear the audio long before their mouths open - their lips are out of sync.

Lip-sync is not an issue when using the simple stereo speakers built into the TV. The digital audio sent with the HDMI data is delayed by each box so that it stays in-sync. Also in reading the forums for my Satellite receiver it has some non customizable lip sync correction built in. But based on the forums, lip sync is still an issue. I suspect that's due to the differences in the Surround sound decoders people own.

To fix the lip-sync I bought a digital audio delay device.

I installed the device. The delay to correct the Satellite lip-sync turned out to be 200 milliseconds, and the Blue-Ray was 50 milliseconds. Each of the 4 inputs can have a different delay which is remembered across power on-offs. If can provide up to 680 milliseconds of delay. My guess is 50-250 ms delay is more than enough to handle typically lip-sync problems.

The audio delay device is made by Felston. Model DD740. It's an excellent, but pricey solution at $250. The 'more expensive' surround sounds have an audio delay capability you can adjust. I highly recommend that you check the specs before you buy a surround sound to make sure it has an adjustable audio delay. This delay is not the room balance adjustment. This is delay specifically to allow you to adjust for lip sync. I had to weigh the expensive delay device vs just buying another surround sound with delay capability built in. There is no 'cheap' delay device that I could find. In the end the device won because it can handle 4 sources, and it fixes the problem once and for all.


Anonymous said...
This comment has been removed by a blog administrator.
Anonymous said...

Don, I'm happy that you posted this information about lip sync delays with home theater systems. It got me thinking about whether I had an adjustment for it on my system which is a Yahama RX-V367. It's turns out I do have an adjustment up to 240ms.. I would encourage anyone with a lip sync problem with their system to check the manual first.