Sound / picture out of sync

Pict

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Fife, Scotland
#1
I notice on Sky Digital that the sound and picture are slightly out of syncronisation. This is not just on my own setup but also on friend's systems as well. This is most noticeable when watching music channels and is really annoying.

Why does this happen? Is there any way of varying the sync between sound and picture to bring them into line?

Thanks.
Pete.
 

PaulR

Dazed and Confused Admin
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#2
I reckon that it's a function of digital TV in general. Both sound and video are run through what is essentially a computer to compress them.

The sound requires less treatment than video so remains nearly unaltered (in time) compared to an untreated signal. The video, however, requires a great deal of heavy-duty processing and this shows up as the video lagging slightly behind the sound.

You don't even have to have a digital receiver to notice this. As all the processing takes place at the broadcaster's end this artifact is noticeable even on analogue TVs as somewhere along the line the signal will have been digitised.

Try watching the live news on an analogue signal - you'll see what I mean.

PaulR

Things might get better in the future as faster signal processors become available so the delay might disappear some day.
 

methos_de

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Sunny old Bristol
#3
Does your friend have the same STB as you ? Maybe its a problem with certain models? I have a Pace SKY+ and my pic and sound sync is fine. Checked on just about all entertainment, movies, sports and music channels. Definately ok here.

Methos.
 
O

Old Fred

Guest
#4
Rebooting (switching wall socket off and on) usually fixes this problem for a while. Poor signal quality can exacerbate it.
 

BarMoo

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#5
My panasonic 30 went out of sync during Channel 4 News the other day. I left it to its own devices as it was fun to watch an interview with a Japanese guy speaking out of sync english :)

Normally, changing to a different channel and then back solves the problem.

Sometimes the sync problem can be broadcaster-side too. Video signals are often passed through kit that employs a frame-store. As far as I recall, one framestore introduces the need to delay the sound by about 44ms (since the audio is not affected and will be ahead of video). Indeed, the more the picture is messed about with - more is the likelyhood of this problem occuring.

These days, its more likely to be a presentation disk server that gets its knickers in a twist. Remember when bbc News 24 started?

Have Fun,

Mark.
 
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