Which time is correct?

[boblalux]

Hope this is the correct forum.
My TomTom (Start20), my Hermle radio-controlled clock (based on caesium clock and transmitted by DCF), and my SONY laptop all EXACTLY give the SAME time.
Why do the television clocks viewed just before news time give times about 20 seconds slower? (I view German television programmes, but I imagine this is the same problem for all 'TV clocks'.

 

[PaulR]

This is a good a place as any.

There are multiple reasons for the delay.

First. Compression of an analogue signal to digital takes a small amount of time. More time is needed for video than audio which is why there is a small, but noticeable, difference between speach and the movement of lips in live broadcasts. This is especially noticeable when there is another live link to an outside broadcast showing on screen behind the presenter, the distant reporter will have a noticeable disconnection between sound and vision.

Second. It takes about half a second for the signal to make the journey to satellite and then back again to earth. It may make the trip more than once - if you are watching a programme which is from a region within the country then it may have been uplinked and then down to the regional office before being uplinked again.

Third. Digital TVs take a litle while to process the signal from digital back to analogue.

Fourth. If you are using a PVR (personal video recorder) which buffers the signal to the hard disc to allow you instant pause of live programmes then this will also introduce a delay as the the signal has to be read from the disc before being passed to the TV.

There may be more reasons and I am surprised that the difference for you is as much as 20 seconds. Another possible cause would be if the Internet is used as a link somewhere. This can add another 4 -5 seconds with ease.

 

[TJExcalibur]

It is because everything French runs slower except for the trains and they are using most of the electricity.

 

[PaulR]

Does the same apply for Germany then?

Incidentally, I think that this digital delay is the reason that UK broadcasters now no longer show clocks. Frankly I'm surprised anyone still does.

Gawd help us if we ever go completely digital on radio as well. At present the most accurate transmission of the Greenwich time signal (the pips) is on Radio 4 Long Wave with R4FM a close second. They might as well close them down for digital.

 

[boblalux]

This is a good a place as any.

There are multiple reasons for the delay.

First. Compression of an analogue signal to digital takes a small amount of time. More time is needed for video than audio which is why there is a small, but noticeable, difference between speach and the movement of lips in live broadcasts. This is especially noticeable when there is another live link to an outside broadcast showing on screen behind the presenter, the distant reporter will have a noticeable disconnection between sound and vision.

Second. It takes about half a second for the signal to make the journey to satellite and then back again to earth. It may make the trip more than once - if you are watching a programme which is from a region within the country then it may have been uplinked and then down to the regional office before being uplinked again.

Third. Digital TVs take a litle while to process the signal from digital back to analogue.

Fourth. If you are using a PVR (personal video recorder) which buffers the signal to the hard disc to allow you instant pause of live programmes then this will also introduce a delay as the the signal has to be read from the disc before being passed to the TV.

There may be more reasons and I am surprised that the difference for you is as much as 20 seconds. Another possible cause would be if the Internet is used as a link somewhere. This can add another 4 -5 seconds with ease.

Thanks for the in-depth reply.
So I assume the TomTom and Hermle DCF77 time signal systems are the "correct" ones
Bob

 

[boblalux]

It is because everything French runs slower except for the trains and they are using most of the electricity.

At least the train systems are maintained!
Bob

 

[PaulR]

Probably...

There's obviously transmission delay for the GPS but that will be much less than for satellite TV as the satellites are much closer to the earth. And maybe they build in some compensation somehow. The clock uses a (very) long wave transmission so will be the most accurate I would think.

Regarding the laptop clock, again there will be some delay but as the time signals are sent out regardless of who receives them it will be miniscule. Again, maybe there's some compensation.

 

[smoggy07]

If I was given the choice I'd take the GPS time as gospel because they depend on having the most accurate time in order to function correctly, they take their time from atomic clocks I think

That said, even the most accurate atomic clock can't tell you what time it is now, they can only tell you what time it was about 2 weeks ago (the work it all out in a chateau in France somewhere based on readings from clocks all around the world)

I'd put the radio clock second, laptop 3rd

The problem with TV time is (as said above) digital processing, satellite uplinking and downlinking

Watch 5 seconds of an SD TV channel then flick over to the HD version and you'll be able to catch the same 5 seconds again due to the nasty delay HD encoding creates

 

[TJExcalibur]

Does the same apply for Germany then?

Incidentally, I think that this digital delay is the reason that UK broadcasters now no longer show clocks. Frankly I'm surprised anyone still does.

Gawd help us if we ever go completely digital on radio as well. At present the most accurate transmission of the Greenwich time signal (the pips) is on Radio 4 Long Wave with R4FM a close second. They might as well close them down for digital.

Not sure about Germany, never been there but I did notice in France everything appeared more relaxed in general. Not sure about the heavily populated places.

 

[sonnetpete]

For sure it's relaxed in the rural parts where I live. A lot of businesses still close for lunch and aren't too fussy about when they open up again. I doubt farmers bother if their watches are 20 seconds out LOL. The church bell in my village still tolls at 7am, noon and 7pm and I wouldn't be surprised if a lot of the retired village inhabitants still plan their day by it. It's true the trains are on time mostly but the health service is certainly up to speed as well...

 

[Analoguesat]

This can also bee seen on the Formula 1. Ive you flick between F1 coverage on RTL & the BBC the coverage from Germany is always at least 3 seconds in front.