GTS (Greenwich Time Signal)
Nick Rodger
I know the exact time is given by the front edge of the sixth pip when listening on FM, but how long is the digital delay on DAB, and is it even longer listening online? Does broadband speed and buffering come into the equation?
Keith Wicks
An answer to the first question — I got the information from the Wikipedia article on Greenwich Mean Time:
“… On digital platforms such as DVB, DAB, satellite and the Internet, the pips—although generated accurately—are not heard by the listener exactly on the hour. The encoding and decoding of the digital signal causes a delay, of usually between 2 and 8 seconds. In the case of satellite broadcasting, the travel time of the signal to and from the satellite adds about another 0.25 seconds….”
I remember once noticing a delay of several seconds between an FM broadcast and the same programme online. I don’t know if this is the norm, but it does mean I don’t trust online GTS. If I remember, I’ll compare an online GTS with my computer’s clock –– which is supposed to be synced to an atomic clock (Apple Europe). But does anyone correct this for delays in transmission… ?
As an example, around 20:0 hrs this evening (29th October 2015), I listened to Radio 4. When GTS indicated 20:0 hours, my computer clock, linked to the Apple Europe clock, indicated 27 seconds past the hour. Exactly what conclusion can be drawn from this is anyone’s guess. Would anyone like to guess?
Graeme Wall, Dave Plowman
Radio 2 had an item about exactly this subject on the 28th October 2015 in the afternoon. Apparently the delay can vary between two seemingly identical radios on DAB. Same thing happens with TV sound from FreeView.
Keith Wicks
I did a further check on clock times at around 2100 hours 29th October 2015.
| My computer clock, linked to Apple Europe | 21: 00:00 | ||
| GTS on Radio 4 Long Wave | 21: 00:00 | ||
| GTS on Radio 4 online | 21: 00:34 | ||
| My domestic radio controlled clock | 21: 00:00 |
I know that the time signals on Long Wave are reckoned to be accurate. But I was surprised that my computer clock agreed with it. My domestic radio controlled clock should agree with it as it is supposed to be accurate to within one second in a million years (or something extreme like that). But I don’t entirely trust it as it was an hour out recently, having been unable to cope with the end of British Summertime.
Brian Curtis
The delay for Internet radio is very interesting! At this moment I’m doing my regular weekly programme on Vectis Radio on the Isle of Wight (www.vectisradio.com ). I have the intriguing situation where I can do a link in the studio and walk through to the production area and hear the end of my link coming out of the "off air" ("off digital ether" ?) monitoring speaker!
I’ve just done a quick check and the current delay this evening is 11 seconds!
Terry Meadowcroft
The delay varies widely from equipment to equipment and transmission path to transmission path. Believe the FM transmission, it is always right.
But, having said that, I have two radio controlled clocks and one radio controlled watch. They are remarkably accurate and even change your clock for you for BST and GMT. The transmissions are on VLF, look here:
https://en.wikipedia.org/wiki/Radio_clock
for details.
I check the pips for accuracy with my watch or the clocks! Dead reliable!
Tony Crake
Here is a little story about audio delays and the "pips"
When I was on Short Wave Transmitters up at Skelton in the early 1960s, the Transmitter site on Ascension Island was being planned… a difficult bit of civil engineering ! (‘they’ even wanted me to go there.. but I declined..)
Eventually there were, I think, Six 250 KW transmitters installed, but the diesel generators were a little short on the job, especially if all six were re transmitting the same programme. What really did the system in was the "pips" on GOS (General Overseas Service ): the peak power required caused the diesels to almost stall and they each uttered a big puff of black smoke. They were not happy!
A plan was mooted to put some sort of staggered time delay in each audio feed to the six transmitters…. permission was sought back in London through ever increasing layers of Senior Management. It was refused! BBC must radiate the pips correctly at all costs!
Keith Wicks
I agree that the BBC should radiate the pips correctly. Although all is well on AM and FM, transmissions by DAB and on the internet suffer from delays of several seconds. So, by these media, the BBC regularly broadcast what will be incorrect time signals when they reach the audience. Presumably the BBC are aware of this, although one can never be sure these days. Is it not ridiculous that time signals keep giving the wrong time?
I think the BBC should cut out the pips on DAB and internet transmissions, perhaps replacing them with something that might come to be regarded as an approximate time signal. Even a silence would be better than an incorrect time signal. The GTS should be reserved for use on services that will not degrade it.
Mike Jordan
Not forgetting the stories of “pip generation”!
Back in pre-history when I was in BH, pips were generated at Greenwich as “negative pips” and sent to BH on a GPO line where there was a ring modulator (or similar) which switched in the 1 k/c tone generated by GPO in Dollis Hill which came by landline via BT Tower exchange. This was supposed to be an incredibly accurate frequency tone.
Later I believe it was generated by a very stable BBC source somewhere in the basement. I would guess the final “death knell” was when Greenwich moved to Herstmonceaux.
The system was supposed to be timed so that it was correct coming out of Droitwich on Long Wave allowing for all the delays on the way.
Takes one back to days of when Big Ben striking could be heard on radio in Parliament Square before hearing it coming down from the tower. Now hearing PIPs etc on sources throughout the house digitally on all routes and analogue is like hearing “Imperial echoes” resounding around the house.
Main and reserve lines from a nasty little room near the base of the Tower to BH and spare via Bush House.
Mike Giles, John Howell (Hibou), Dave Mundy
I know a certain sound person who did an attachment from TV to Northern Ireland: he worked on a radio programme where the presenter kept crashing the pips, so my anonymous friend, oblivious of the high level approval required, recorded them and played them in when the presenter had finished!
I believe the same anonymous friend, to relieve the boredom, plugged the pips to two channels on the sound desk and faded them up alternately.
I heard a story about a sound operator who recorded the pips because the regional news always over-ran and it was the only way to get all 6 pips broadcast before the national news opt-in!
Bill Jenkin
The version of that which has been told to me was that in a London Control Room cons they had been known to put the pips on six channels and got each pip on a different channel. The problem was trying to explain how one of the middle pips was missing if you got it wrong.
Alex Thomas
I well remember working with the RTE political correspondent on UK Party Conferences in seaside towns like Brighton, Blackpool and Scarborough.
We called him the “Leprechaun” and he seemed completely unfazed by the inability of Dublin’s CAR to get their act together and accept the feed.
“Don’t worry,” he used to say, “We don’t play the Angelus at 6 o’clock until we are ready.” It often went out several minutes late.
We had a system known as “ The Barber’s Shop” where various BBC regions had a slot or window in the first half of Nationwide.
Each region booked its slot and then there was about 30 seconds to drag the previous journo or guest out of the chair and insert the next “victim” into the chair. It all depended on very strict timing.
I was at Brighton at a Tory Party Conference when Sir Keith Joseph arrived a little bit late. We stuck him in the chair and the interview over the line began almost immediately.
I could see that he was a bit unhappy with the interview as the veins on his temples were starting to bulge.
The interview ended abruptly and I dragged him out.
“Who on earth was I talking to?” he said.
Before I had a chance to say “Leeds Newsroom” (his constituency was Leeds North East) Selwyn Cox manning the static camera leaned round the camera and said “Norwich, sir”
“Why the hell would I be talking to Norwich” said the flustered and misinformed Secretary of State for Education.
“No time to explain” I said as I dragged the Look East journo into the seat.
Great times and such fun!
Mike Jordan
When I was working in London Switching Centre in the late 1960s, we used to use network distribution to feed pieces into regional news programmes.
All the bookings were made to the minute and as the person operating the “return feed to network” key, I was often responsible for getting extremely close to cutting off inserts to the regions. Kept one on one’s toes though.
Similarly in General elections at the time, London Switching Centre was the South East “hub” to route various OB sites/results over a single line to TC.
None of the complexity of nowadays and still looked OK!
Big Ben
John Howell
There used to be a horn loudspeaker adjacent to the BH clock for relaying the sound of Big Ben "at approximately its natural strength". I’ll bet the guests at the Langham Hotel appreciated the service!
Keith Wicks
I’ve read that the speaker was installed to placate neighbours who complained that the new building shielded them from the distant sounds of Big Ben that they used to hear. But is this true?
I ask because the speaker was installed on the side of BH opposite the Langham Hotel. But Big Ben is to the southeast of BH, so the only neighbours shielded from the sounds of Big Ben would have been living in Duchess Street, to the North of BH. Can anyone explain why the speaker was apparently installed in the wrong place?
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John Howell, Rex Palmer, Keith Wicks
The loudspeaker was installed in the early 1930s, soon after BH was completed: the speaker is pictured in "Broadcasting House" published in 1932: see picture above. This was before the time when The Langham became BBC offices. The BBC occupation of The Langham started in 1945, before it later reverted back to being a hotel.
Geoff Fletcher
Now, who is the guy on the roof?
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Pat Heigham
Arthur Askey or Richard ‘Stinker’ Murdoch, as on the Radio "Band Waggon" they had a fictitious flat on the roof of BH: – (oh, OK, that wasn’t until 1938, so the figure could be Dr. Who!)
Mike Jordan
The Langham was BBC offices/overnight rooms for shift staff and a really fabulous BBC club – long gone and reduced to a nasty place in Western House (which I believe was originally built as a car show room).
I was outside The Langham on OBs when the Queen re-opened BH or something. Usual case of taking BBC power from a corridor at the side and of course it failed just before the show!
There were “steam pipes” across Portland Place from BH basement which we also used for the TV tielines to The Langham from BH – wonder if it is still there?
The 1932 picture and many more are at:
http://flashbak.com/twenty-five-stunning-pictures-of-bbc-broadcasting-house-in-1932-30877/
(Keith Wicks)
The photos clearly show the houses where Egton House is now, that forced the “Catslide” sloping roof on the top floors where Control Room was before the war. That has of course now gone since BH was re-built this time around!
Pat Heigham
If Big Ben has to be shut down for repairs, will a recording be played?
Keith Wicks, Dave Buckley, Pat Heigham
They probably would use a recording of Big Ben. It was apparently done during WW2 as it was found that the ‘tone’ of the main bell changed due to the weather and this change could be used to work out what the weather was like over London. That could have helped the Luftwaffe! But on the other hand, maybe put out the message that London had not succumbed to them knocking out its iconic symbol.
Mike Jordan
If my memory serves me correctly, the clock was shut down for a while in the 1960s and alternatively one called “Big Tom” was used. I know we set up microphones and lines to BH.
Pat Heigham
I now remember that during an earlier maintenance, Great Tom in St. Pauls was the understudy.
(From a Wikipedia Q & A site:
Q: Are the chimes on BBC Radio 4 transmitted live?
A: At certain times, yes. If you visit the belfry, you can see the microphones hanging down from the ceiling. When Big Ben is out of action, Great Tom from St. Paul’s Cathedral does the honours. Or you hear the "pips" which mark the hour).
Is the mic still a ‘ball & biscuit’?
Dave Mundy
When I was at school in Nottingham I was told that ‘Little John’, the largest bell of the Council House chiming clock, had been used as a replacement for Big Ben. Now all the papers are reporting that Notts. Council have offered to do it again! Apparently, it is the most accurate electric striking clock in the world.
Pat Heigham
There’s a lovely story – maybe a Ronnie Barker source – that when there were works going on in the clock tower, a programme came out early, Continuity faded up the Big Ben mic ready, and the immortal broadcast went:
" ‘ere Bill, chuck over the hammer!" "Bong"
Nice, but probably invented!
Bell rings reminds me of a comedy play (I was Grams) involving a character oversleeping on a Sunday. He wakes up to church bells which sound wrong. He realises that he is supposed to be on bell 3 – panic journey to church and all befalls him etc.
It is impossible to edit out one bell from a peal, so I organised a special recording at Guildford Cathedral on their practice night – (I knew the right people), and asked for a standard ring down of 8 with the 3rd missing – leaving a gap, then a single recording of the missing bell – later laid up in sync on the second track of the TR90 tape. So a fader tweak when he eventually took his place in the bell tower to bring it right.
The ringers wanted to know why such a particular recording was necessary. I felt I couldn’t tell them it was for a comedy show (being on hallowed ground) so I faffed about an explanation of harmonics build up!
Well, they might not have done it, otherwise, but in today’s atmosphere, maybe they would be amused.
Peter Neill, Bill Jenkin
Of course, it was the advent of digital broadcasting (both satellite and Freeview) which caused the demise of the in-vision clock ticking the seconds up to the Ten O’clock News, and cue dots for live TXs. (Although they still use them sometimes on ITV/Ch4 to cue in the commercial breaks.)
The “filler” countdown up to the hour on the News Channel (formerly known as News 24) gets away with it because they don’t say what it’s counting down to.
Digital v Analogue – Synching Sources
Alec Bray
On a related theme. Production could not have mixed in the live sound from the “Proms in the Park” (12 Sep 2015) as the pictures from Hyde Park (at least) had a countable delay from the pictures from the Albert Hall. Russell Watson was at least half a bar out in his singing of “Jerusalem” and other songs. Presumably the feed from the Albert Hall to the Hyde Park screens suffered a delay. This was a really jarring visual, seeing a world renowned soloist seemingly out of time.
Also, the display monitors inside the Albert Hall had a noticeable delay compared to the transmitted picture. Difficult to capture this, but in this still, the display on the arrowed monitor is some “frames” behind the picture as transmitted. (and I don’t think it is the violinist’s bow giving a false positive).
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This is not a problem which would have happened in the days of CRT monitors and old style projection television screens. Modern technology has not necessarily produced a better viewing experience.
Analogue 1, Digital 0
… Come back Genlock, all is forgiven …
Jeff Booth
Flat screen tellies have a processing delay of (a few) frames. Different by manufacturer. Hence the issue.
The RW sync was likely due to much the same problem. Additionally, delays through video synchronisers and links wouldn’t have helped!
Dave Plowman
You see this all the time on live programs like “Newsnight”. In-shot monitor of an OB out of sync. Anything with any digital processing introduces a delay.
Pat Heigham
Please don’t get me going on about sound/vision sync on digital TV.
My guru tells me that it’s no good chasing sync with the audio delay facility built in to players and TVs as the processing time for picture depends on how complex (or busy) the image is at the time.
There used to be a ‘sound-in-syncs’ transmission system. Could not some clever person design a splitter to separate the audio and picture signals and let them out of the decoder at the same time?
Alec Bray
With the “Last Night of the Proms”, my issue was less technical than aesthetic.
Mr and Mrs Viewer at home are watching a top rank Music Programme: a large orchestra and a very large choir all singing in time with the conductor.
But they are SEEING three distinct, and time-separated, set of images.
1. The direct visual feed as broadcast
2. The "PA" display on digital monitors in the Albert Hall, the image delayed by "some" (as unspecified) frames
3. The OB feed from Hyde Park which is countably delayed from the direct feed from the Albert Hall.
The various picture streams and the music do not match, and it was quite disturbing – (even) my wife commented on it!
Surely it could be sorted: they have remote choirs on things like "Children In Need" all singing in time!
The “Children in Need” ‘singalong’
Jeff Booth
In order to get all the regions/OBs singing in sync, the backing track has to be sent from London so they can hear the music.
Sounds simple, but…
The BBC regions have switched talkback from London (and pre coding and mux vision and audio feeds).
The issue is with how long the vision from the region/OB etc. takes to get from/to London. With the regions that have fibre, the delay is only half a dozen frames or so. If a satellite is used (from a remote OB) then the delay can be several seconds. With reverse vision over the satellite, this delay is doubled.
So, during the day, the reverse audio to each region/OB is used to send either timecode or a clapperboard to get the exact delay (there and back) in frames/milliseconds.
The backing track is loaded into a DAW (Digital Audio Workstation) and each output is adjusted to allow for the delay established above. There could be a dozen feeds of the audio (all out of sync with each other) going from London.
So by the time the audio gets to each place and back, it appears in London ‘in sync’.
However, the backing track sent to the region is not used on air. The music is played to the performers but only the clean voices are sent to London.
The backing track that matches the longest delay is used on TX and the clean voices mixed by the Sound Supervisor as the vision is mixed around.
