RF transmission delay

. During this time he pretends to be dumbfounded, or, pretends to be far, far away.

en anchor and correspondent.

There is a few seconds delay in all digital TV broadcasting since its takes time to encode a video signal into an MPEG bitstream and a similar time to do the reverse. MPEG coding compresses data by sending the *difference* be tween successive video frames and so needs a buffer of about 2 seconds to c ope with sudden complete changes in the image.

When simultaneous analogue and DTV broadcasting was available, the DTV sign al was always 2 to 4 seconds behind.

This is a real pain when broadcasters do person to person interviews from a studio to a remote location. It's like when NASA was talking to astronauts on the moon.

Otherwise it goes unnoticed, except when you change channel on a DTV set - there is a couple of seconds delay then too while data buffers and complete frames are reconstructed.

.... Phil

Both ends have a copy of the script so the guy at the far end knows the running order and can guess when to start his answers. What he cannot know in advance is the exact moment that the studio will switch to him.

A bit like the DVD transcript in the Dr Who programme titled "Blink".

There is almost always a turn around time when they are linking to a remote outside broadcast team since unless they can get terrestrial line of sight microwave link or fibre broadband the return video signal has to go via one or more a geostationary satellite(s).

But in the UK at least there has been a 7-10s delay on transmission of "live" TV reporting ever since at least the IRA era so that they could pull the plug if an atrocity took place with the cameras rolling.

You only really notice it if like on New Year's Eve you can compare TV broadcast "realtime" with the actual reference of true time.

Slightly more if it is from a satellite feed. It is a bit annoying when they broadcast incorrect "precise" time signals on digital radio and TV.

Not quite but there is a noticeable lag as far as the presenters are concerned. It is easier if both ends have a copy of the same script.

Its a bit quicker than that. First index frame and it syncs again.

The satellite delay is quite insignificant when compared to the digital compression/decompression delay, especially for effective compression. Sometimes they try to use a less effective but lower latency compression for this kind of work, but when a low capacity digital link has to be used it is not really possible.

Here is is even more, I think 30-60 seconds, and it is also used to insert live subtitling for the deaf. But this does not affect the above, as the delay affects the finally mixed content only, not the interactions between reporter and studio.

The extra delay for a single satellite feed is only 1/4 second one-way or 1/2 second two-way. So most of the "2 to 4 seconds" is not from that.

Presenters get extensive training for coping with the delay, amongst that is strictly adhering to the script, and how to cope with collisions. When there is a collision, the remote reporter should stop talking and wait for the presenter to give directions.

Unfortunately, a common problem is that the talkback link to the remote reporter inadvertently gets audio from the studio while the reporter is talking, and he hears back is own voice with a long delay. Some people can cope with that, but most will pull out the earpiece and can then easily miss the next question. Often in such cases they have a fallback scenario where they finish their entire story in a monologue and hand back control to the presenter.

And similar delays are experienced even when the correspondent is in the same city. As anyone who has watched DTV in the last 10 years must be aware of.

But obviously not brain dead morons like Martin Brown.

.... Phil