Greenwich Time Signal

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Graph of the six pips

The Greenwich Time Signal (GTS), popularly known as the pips, is a series of six short tones broadcast by many BBC radio stations at the end of each hour to mark the precise start of the following hour. First introduced in 1924, continued use of the time signal on radio is currently in some doubt as the unavoidable time lags associated with digital broadcasting systems make it less reliable as an aid to calibration.

1 Structure
2 Usage
3 History
4 See also
5 External links
6 References

[edit] Structure

There are six pips (short beeps) in total, which occur on the 5 seconds leading up to the hour and on the hour itself. Each pip is a 1 k Hz tone which, for the five leading pips, lasts a tenth of a second, while the final pip lasts half a second. The actual moment when the hour changes – i.e., the "on-time marker" – is at the very beginning of the last 'long' pip.

GTS Time Signal

The six pips

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When a leap second occurs (exactly one second before midnight), it is indicated by a seventh pip. In this case the first pip occurs at 23:59:55 (as usual) and there is a sixth short pip at 23:59:60 (the leap second) followed by the long pip at 00:00:00. The leap second is also the explanation for the final pip being longer than the others. This is so that it is always clear which pip is on the hour, especially where there is an extra pip that some people might not be expecting. Prior to the conception of leap seconds, the final pip was the same length as the others.

Although normally broadcast only on the hour, the signal is also generated at a quarter-past, half-past, and a quarter-to every hour. It has occasionally also been broadcast inadvertently at these times.

[edit] Usage

The pips are used by a number of BBC radio stations to mark the start of the hour. On BBC Radio 4, the pips are replaced at the start of the news bulletins broadcast at 18.00, 22.00 and midnight by the chimes and strokes (popularly: the "bongs") of Big Ben, with the first stroke signalling the start of the hour. In 1999, pip-like sounds were incorporated into the themes written by composer David Lowe to introduce BBC Television News programmes. They are still used today on BBC One, BBC World News and BBC News. The pips can also be heard every hour on the BBC's worldwide radio station BBC World Service.

In the late 1980s, BBC Radio 1 featured the pips played over a station jingle during Jakki Brambles early show and Simon Mayo's breakfast show. The pips are also currently featured on The Chris Moyles Show on BBC Radio 1 at 6.30am just after the news, 9am as part of the Tedious Link feature, 10am (at the end of the show), and sometimes before Newsbeat bulletins. They appear on BBC Radio 2 at 7am (during Sarah Kennedy's show), 8am (during Terry Wogan's breakfast show) and at 5pm (currently between Steve Wright's and Chris Evans's shows).

In the past, the pips were also broadcast by the BBC Television Service although this practice had been phased out by the 1960s.

Talking, playing music or making any other noise while the pips are sounding is frowned upon at the BBC, and doing so is commonly known as 'crashing the pips'. This is most often referred to on Wogan's show, although usually only in jest since the actual event happens only very rarely.^[1]

As a contribution to the 2005 Red Nose Day charity day, the BBC developed a "pips" ring-tone.

Bill Bailey's self styled comedy included the BBC Rave, paying homage to the "pips", the footage can be seen on his Part Troll DVD.

Time pips are used elsewhere in the world; for example on ABC Radio in Australia.^[2] ABC Radio

In Hong Kong, similar pips are used on RTHK's radio channels for the same purpose and in the same way. The signals, which are provided by the Hong Kong Observatory, are broadcast every half hour (except in the late hours when the pips are broadcast only on the hour) immediately before the news headline reports.

[edit] History

The pips have been broadcast daily since 5 February 1924, and were the idea of the Astronomer Royal, Sir Frank Watson Dyson, and the head of the BBC, John Reith. The pips were originally controlled by two mechanical clocks located in the Royal Greenwich Observatory that had electrical contacts attached to their pendulums. Two clocks were used in case of a breakdown. These sent a signal each second to the BBC, which converted them to the audible oscillatory tone broadcast.

The tone on the line was inverted; that is to say, the signal sent to the BBC was "on" when no pip was required, and was pulsed "off" when a pip should be sounded. This allowed a fault on the line to be detected immediately.

Today the pips for national radio stations and some local radio stations are timed relative to UTC, obtained from an atomic clock located in the basement of Broadcasting House that is synchronised with the National Physical Laboratory's 'Time from NPL' and GPS. On other stations, the pips are generated locally from a GPS-synchronised clock.

The BBC compensates for the time delay in both broadcasting and receiving equipment, as well as the time for the actual transmission. The pips are timed so that they are accurate as received on long wave 160 km (about 100 miles) from the Droitwich AM transmitter, which is the distance to Central London.

Newer digital broadcasting methods have introduced even greater problems for the accuracy of the pips: on platforms which use digital compression, such as DAB, digital satellite, Freeview and Internet transmissions, the pips are no longer exactly on the hour. The encoding and decoding of the digital signal can cause a slight delay, usually around 2 seconds. In the case of satellite broadcasting, the travel to and from the satellite adds a further delay of around 0.25 s.