Freeview Question.

[paul kersey]

I live in a bungalow with the kitchen being next to the lounge. We have a 14'' TV in the kitchen and a 37'' TV in the lounge. Each tv has its own aerial with the aerials being mounted, one above the other on the same chimney.
When the two TVs are tuned to the same station, why is there a slight time difference between the two tv's that results in an echo effect which distorts the sound on both TV's and means that watching the TV in both rooms is at least un-comfortable if not in-audible?In theory, would this disappear if we had one aerial with a splitter ?

[MartinU]

No, almost certainly it wouldn't. I imagine that the different delay is occurring at the Freeview decoders in (or connected to) the two TVs which are delaying the signal by slightly diffferent amounts. It's the price you pay for digital broadcast. Unless... the two TVs happen to be tuned to different transmitters, then another effect comes into play as well.

Long ago (long before digital) I could receive two ITV regions. I happened to have my VCR's tuner tuned to one ITV station and playing sound through my stereo, when I switched my TV over to the other ITV region, with the sound up. There was a noticeable time delay between the two: a fraction of a second, but long enough to be noticeable as slight reverb on the sound. Probably due to the different signal paths from the studio to the two transmitters, and then from the transmitters to my aerial, though you'd need a distance of 30,000 km to give a time difference of 100 msec, so maybe there was some sort of signal-processing delay in one of the transmitter feeds as well.

[Arfur Teacake]

What technology has failed to do is provide a digital convertor box that feeds out to RF,
so that you could leave it in the loft and feed all your old and new tellys via normal splitter in the usual way through the aerial socket with a uniform timed signal.

[Steve Crook]

Try it with different radios around the house, all tuned in to radio 4. One gets its signal direct via VHF, one is on DAB, another is via the cable. When the time pips go off you hear how out of synch they all are as it goes pi-pi-pip, pi-pi-pip, pe-pe-peep

Steve

[MikeB]

As Steve points out, this delay is most noticeable on radio (we all tend to have several radios around the house, generally tuned to the same station, but using FM, DAB, internet, etc). The tuners in your TV's, recorders, etc, are likely to be different, and thus have a slightly different processing time. Since most people tend not to watch the same thing in different rooms at the same time (couples will often say they want a smaller TV in another room so that she can watch her soaps, while he can watch his sport!), the slight delay is not normally an issue.

Since the delay is in the different tuners (unless you do have them tuned to different transmitters, as MartinU pointed out), there is not a lot you can do about it, although a 14" TV is pretty unusual these days, and its possible that a replacement would have a faster processing speed. Although we operate all the TV's off several main feeds at work, I've yet to notice a difference as to picture/sound between them (the 19"-26" TV's are usually on a digital signal alone, and the larger ones on digital/HDMI). It might be that one of the receivers is particularly slow, and a replacement box might be then in sync with the other TV.

The effect was worse before digital switchover, when you could have analogue, digital and satellite feeds all at the same time. There is roughly a second or two between each of them, and customers would get very confused (although we seldom set up the analogue signal anyway). There is of course still a delay between freeview and freeview HD signals, of about two seconds, and the Sky feed is also slightly different.

PS - a very similar question was asked on UKFree.tv a while back (12th May 2010) http://www.ukfree.tv/fullstory.php?s...00&PGSTART=200 - the answer was

Not all decoders will take the same time to decode the signal, the only way you can get around the problem is to have exactly the same make of decoder for each set

- although I must point out the person asking the question did have a very complicated setup!

[Pricey]

I have nothing practical to offer on this one but just wanted to share my own frustration that digital radio Test Match Special and Radio 5 live coverage is always at least a few seconds ahead of Sky and ITV TV coverage, which means I can't easily replace the awful TV commentaries on both with the far more enjoyable BBC radio commentaries.

[autolycus]

There are many possible ways around this problem. Some are mentioned here

http://www.botecomm.com/bote/radio/radiodelay.html