Hi, All,

Lip Sync (or loss thereof) is apparently the price we pay for progress.

I have not followed the latest in video and audio compression tools, 
but the problems started as soon as we had digital frame synchronizers 
that could delay incoming video so that it was in-time with plant video.

Since the two reference generators were not in sync, the delay was 
variable. Good design was to use a tracking audio delay at the frame 
synchronizer.

Enter digital production switchers...these had variable delays based on 
the amount of effects (some would compensate) and the audio console in 
the paired audio control room needed to have a delay to match the 
production switcher.

Then, of course, when moving from uncompressed video in the plant to 
compressed video transmission, what Tom said...

Now, it seems that cable companies MAY be recompressing the DTV signals 
to meet their bandwidth requirements, so there is another chance for 
audio and video to get out of sync.

I went into full-time audio tape restoration in the middle of this and 
have not kept abreast of the developments in video system design. I was 
part of the team that put in several early HDTV pilot facilities, but 
left after the first few mostly file-based plants were built.

I'm sure others know more, but keeping audio and video locked together 
has been a challenge for probably close to a quarter century. A single 
frame delay is not all that noticeable. Add a few more and it becomes 
annoying.

Cheers,

Richard


On 2014-03-12 2:01 PM, Tom Fine wrote:
> The audio out of sync with video seems to be one of the many prices of
> "progress", moving to digital TV. As I understand it, different digital
> compression and transmission protocols are used to send audio and video,
> and often don't arrive at the viewer's TV set at the same time.
> Hopefully one of the broadcast technical pros on the list can explain
> this better.
-- Richard L. Hess                   email: [log in to unmask] 
Aurora, Ontario, Canada                             647 479 2800 
http://www.richardhess.com/tape/contact.htm Quality tape transfers -- 
even from hard-to-play tapes.