Re: [LEAPSECS] BBC beeps

From: Ed Davies <ls_at_EDAVIES.NILDRAM.CO.UK>
Date: Fri, 05 Aug 2005 13:31:08 +0100

> "Clive D.W. Feather" wrote on 2005-08-05 07:48 UTC:
>
>>At the other end of the scale, BBC radio transmits the "Greenwich Time
>>Signal" on many channels on many hours, so the public expects it to be
>>correct.

Markus Kuhn replied:
>
> Oh, those good old analog broadcast days are soon gone.
>
> With the move to MPEG audio compression on many radio and TV broadcast
> channels, both the transmission latency and its variance have risen to
> several seconds. Unfortunately, the standards committees defining the
> DAB and DVB digital audio and video broadcasting standards neglected to
> define the exact phase offsets to be maintained between the transmitter
> and the receiver clock. As a result, the BBC beeps can be several
> seconds off these days and it is not easily possible for the broadcaster
> to compensate for the transmission delay. I'd expect them to sooner or
> later give up and remove sub-minute accuracy clock displays (such as the
> famous beeps) from these broadcasts.

A discussion of this a while back on this list caused
me to ask a retired BBC Radio (Radio 4, mostly) studio
manager about their timing - specifically about whether
they ran the studio operations a few seconds ahead of
local civil time to allow for digital transmission
delay. My recollection of the conversation is that he
said that they don't run ahead, they were aware of the
problems with the delay of beeps on digital transmissions,
that they were pretty unhappy about it and were, at the
time he retired, considering suppressing the beeps from
the digital signals - no time check being better than a
wrong one.

They run their schedules pretty accurately - to the
second or so. One of the more unusual skills
presenters are respected (or not) for (at least in
his rather specialised circles) is the ability to
smoothly end the programme at exactly the right time
even from an ad-lib live discussion.

Hence my recent comments about civil vs SI seconds
in TV; TV being a better illustration because of the
natural importance of stable short period times such
as frame rates.

Ed Davies.
Received on Fri Aug 05 2005 - 05:31:35 PDT