Belfast Telegraph

Saturday 27 December 2014

Digital, analogue and the paradox of time

Grierson Gower ( letter, 16 August ) is concerned about the time delay between the digital and analogue time pips, and asks which is correct.

A moment's thought shows that the earlier signal (the analogue signal) must be the correct one, unless the BBC has discovered the secret of time travel, since it is derived from the Greenwich signal, which in turn comes from an atomic clock. The delay of six seconds Grierson Gower experiences varies depending on the receiving set and the region of the listener. In my area it is less than six seconds.



The BBC seems to be rather coy over the implications of this disparity. Various letters and queries by me about it have been quietly ignored. This may relate to the Corporation's obsession with presenting digital broadcasting as the new technological wonder, and their plans to kill analogue TV and FM radio, which has the correct signal – and far better quality sound for music broadcasts.



Perhaps Dr Who, a Time Lord, can offer some clarification and intervene with his sonic screwdriver? Some of the BBC mandarins certainly seem to have a screw loose.

Peter Curran, Kirkliston, West Lothian



Grierson Gower asks which time signal is correct, that from digital radio, or that from analogue. The simple answer is, neither.



Although the processing of the digital signal adds a delay, the radio signal itself is travelling at the speed of light, and is delayed a millisecond for every 186 miles it travels. Probably not significant if you are trying to adjust your watch, but it could be in some circumstances.



The idea of sending time signals by light beams or radio waves is one of the concepts behind Einstein's theories of relativity, which lead to the conclusion that there is no absolute time, only time relative to the observer. There is no simple answer to the question "What time is it?"

Paul Dormer, Guildford



The situation regarding time checks is more complicated than Grierson Gower states. We have analogue and digital radios and a digital TV which also receives digital radio. If all three are tuned to the same station it is quite possible when moving between rooms to hear the same words or music three times in quick succession, first on analogue radio, then on TV digital and, lastly, on the digital radio itself.

And they say there are too many repeats on TV!

Gordon Whitehead, Copt Hewick, north Yorkshire

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