Re: The Lords get the Pip


"Richard Evans" <R.P.Evans.NoSpam@xxxxxxxxxxxx> wrote in message
news:1qAve.6872$%O1.881@xxxxxxxxxxxxxxxxxxxxxxx
>
>
> Scott wrote:
>
> > On Sun, 26 Jun 2005 15:29:37 +0100, "Stephen Peterson"
> > <nospam@xxxxxxxxxxxxxxxxxx> wrote:
> >
> >
> >>"Richard Evans" <R.P.Evans.NoSpam@xxxxxxxxxxxx> wrote in message
> >>news:lqnve.4481$rz1.2003@xxxxxxxxxxxxxxxxxxxxxxx
> >>
> >>>
> >>>Or another method might have been to define a standard for the
timing of
> >>>audio at the receivers speaker.
> >>>
> >>>Eg, the timing of a particular audio frame to the speaker could
be linked
> >>>to the time when the start of a particular TX frame was received.
> >>>
> >>>That way they could calculate exactly what time each audio frame
would
> >>>reach the speaker, and hence work out the correct moment to add
the pips.
> >>>
> >>>Richard.
> >>>
> >>
> >>People interested in accurate time generally use a GDS or MSF
receiver these
> >>days, not Radio 4 as their standard.
> >>
> >>That said, it is annoying that different radio sets around the
house deliver
> >>the output at different times. Surely the best way for the BBC to
correct
> >>this is to originate all programmes (including the pips) a few
seconds early
> >>and then delay the output to each transmission chain by different
amounts.
> >>This should be done in such as way that the inherent delays in
each chain
> >>plus the delay added by the BBC to that chain are all equal.
> >>
> >>Stephen
> >>
> >
> > My understanding is that the delay depends also on where the
> > transmitter is
>
> If a transmitter is 75Km away, it will take about 250us for the
signal
> to arrive. This delay would however be the same for FM. I also
seriously
> doubt that human perception could spot such a brief delay.
>
> On FM there might however be issues over the time taken for an audio
> feed to reach a distant TX site. This could be fixed if the pips
were
> added at the TX site, based upon some type of accurate time source.
>
> Alternatively the FM audio feeds could be time stamped, and then
> buffered at each TX site in a way similar to DAB data feeds.
>
> > and the type or receiving equipment used.
> That was my point. Different receivers may introduce slightly
different
> delays.
>
> I noticed this when I got into my car and switched on the stereo,
before
> turning off my personal stereo. The result was a significant echo.
Not
> huge but enough to be annoying.
>
> If a standard was adopted to link timing of audio frames to timing
of
> transmission frames, then two receivers tuned to the same DAB feed
would
> produce the same sound at the same time.
>
> As far as the pips are concerned. The BBC presumably have control
over
> the timing of Transmission frames on their DAB network. They can
work
> out which audio frames will be associated with which transmission
> frames. Therefore they could work out exactly when an audio frame
would
> reach the speaker on a compliant receiver. Therefore they could work
out
> an exact point in a particular audio frame for each pip.
>
> Richard.
>

Not as easy as that.

For a start the signal does not go from source to Tx. In most cases it
has to go through the local studio centre per region to allow for
opt-outs. To get a signal from London to, say, Pontop Pike in Tyneside
it very likely doesn't go up the east side of the country: most
signals from London go at least via Brum or Manchester.

Second, the BBC is responsible neither for distribution nor
transmission, that is all the responsibility of Crown Castle - now
called Gridcom - who mainly use BT for distribution.

Where BT run it is anyone's guess. Remember the fire in a tunnel in
Manchester last year (do a Google search in 'Guardian Telephone
Exchange')? One of my customers with HQ in Swindon lost circuits to
Huddersfield and Lincolnshire. Cheshire Police, Chester Division PR
local system lost four out of ten sites.

BT use a combination of fibre and microwave networks. Such networks
are built in rings connecting, let's say four locations A-B-C-D-A in a
ring. The 'normal' route for a circuit may be A-B-C-D, but if any part
of that route fails it will automatically reroute to A-D direct. There
will probably be a significant difference in the path length for the
two routes.

Every time the signal is mux'd up or down and/or travels over a fibre
or radio link the signal is subject to delay, and that may happen many
times as the signal wends its way to the Tx site. In some cases a
short path over co-ax mux may take longer than fibre or microwave. I
did a quasi-sync system for the AA in Manchester years ago; the signal
took longer to get from Cheadle to Winter Hill on co-ax and analogue
mux than it did from Cheadle to a site near Carlisle on fibre and
digital mux.

Ultimately, there is no simple answer, other than, as others have
said, using GPS, MSF, or Radio 4 LW on 198KHz from Droitwich - which
in audio terms is probably the nearest you will get.


--
Woody

harrogate2 at ntlworld dot com


.

Relevant Pages

  • Re: How could they have been so wrong?
    ... > show that the cross talk recordings were made through a radio receiver. ... > Although the Committee on Ballistic Acoustics should have tested heterodynes ... > provided by the committee showed AGC acted on audio. ... > different frequencies produce a beating of signals at an audio rate. ...
    (sci.electronics.design)
  • How could they have been so wrong?
    ... show that the cross talk recordings were made through a radio receiver. ... Although the Committee on Ballistic Acoustics should have tested heterodynes ... provided by the committee showed AGC acted on audio. ... different frequencies produce a beating of signals at an audio rate. ...
    (sci.electronics.design)
  • Re: DTV Reception Maps
    ... There is two values that affect digital signals most. ... level of the primary wave compared to the reflected waves. ... out the COFDM receiver didn't work right. ... In the first test in Baltimore done by Sinclair the COFDM receivers worked very well. ...
    (alt.tv.tech.hdtv)
  • Re: EGNOS/ESTB
    ... >> I have left my monochrome etrex Vista powered up ... > In car it may be difficult with buildings around. ... You carefully snipped my next sentence "When I held the receiver out of the ... The point of my message was that I had been receiving very strong signals ...
    (sci.geo.satellite-nav)
  • Re: The Lords get the Pip
    ... The other 1/2 is at the receiver, which has to wait for the delayed bits to arrive before passing the data onto the next stage. ... If you add to this the delay added to fix timing differences in telecommunication networks, then you have quite a significant overall delay that is not caused by the receiver. ... The BBC DAB mux is distributed to the transmitter sites by satellite, ...
    (alt.radio.digital)