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Quite often I observed that whenever a caller participates in a live TV talk show, there is delay of time to respond a particular question asked by the compère of the program. This delay is due to the fact that signals take more time to reach the participant compared to a TV watcher. May I know the reason for such delay?

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    $\begingroup$ The telly guys delay the broadcast intentionally, so that you cannot take advantage of everything being live. eg. When you try to swear the Queen in UK on BBC, they cut the broadcast before everyone else hears it. $\endgroup$ – Gonenc Jul 14 '15 at 10:54
  • $\begingroup$ @gonenc I doubt that's the case with e.g. foreign correspondents or experts on live link-up on news programmes, for which there is also a noticeable delay. $\endgroup$ – innisfree Jul 14 '15 at 12:12
  • $\begingroup$ in any case, let's try to address the physics aspects of the delays, rather than whether it's judicious for TV broadcasters to insert an additional delay $\endgroup$ – innisfree Jul 14 '15 at 12:14
  • $\begingroup$ @innisfree: gonenc is correct, "live" TV is intentionally broadcast delayed by a few seconds for editing purposes, even for foreign correspondents as this Skeptics.SE Q&A show. $\endgroup$ – Kyle Kanos Jul 14 '15 at 12:55
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It is not that the interviewee experiences a longer delay - but that you see the whole scene delayed by the same amount.

Delays are caused by a number of factors:

  • sound is conveyed in packets that are digitized, compressed, and converted at various points along their path: at each point they experience at least "one packet's worth" of delays (can't send the packet until you received it).
  • satellite links travel considerable distances: if you use a geostationary orbit satellite (about 36000 km) it would take the radio wave over 1/10th of a second to go up and down (and more delay in the satellite...). If the satellite is not directly overhead the delay is even greater

Now you as the viewer experience a delay as well, due to the same reasons - but you don't notice this because everything coming from the studio is delayed. But the signal coming from the interviewee is delayed more.

Incidentally the delay is longer with video as there has to be a certain "buffer" built in to make sure packets arrive "in order". The sound packets are synchronized with the visual packets - the latter are much bigger and drive the transmission delays. As the quality of the link degrades the protocols build in extra time to "fix mistakes" - retransmission on error for example.

Sometimes the image goes "blocky" for a moment - that's when the error rate was too big to correct for. But because the delay only matters briefly during the handoff in the conversation it is usually considered better to buffer and get high quality, than to minimize delay and get more errors.

When you are Skyping you have less delay, and more frequent loss of quality. That is the trade off made when a medium is used for direct two-way communication. But for TV, relying often on satellite links, buffering is the way to go. You just don't notice it except when an extra "round trip" is suddenly added.

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It is more often the case that the broadcast is delayed a few seconds so that if the phone-in participant says something that the show's producers don't like it can be easily censored.

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