Greenwich Time Signal

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The Greenwich Time Signal (abbreviated GTS), popularly known as The Pips, is an audible series of short tones marking the precise time, broadcast on many BBC radio stations at the end of each hour. The signal has been used since 1924, but its long-term use is now in doubt because of unavoidable time lags associated with digital broadcasting systems.

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.

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

Usage and homages

The pips are used on some BBC official radio stations to mark the start of the hour. On BBC Radio 4, at start of the 6 o'clock evening, 10pm and midnight news the pips are replaced by the chimes and strikes of Big Ben, where the first strike represents the start of the hour. In 1999, pip-like sounds were incorporated into BBC Television News by composer David Lowe. This included news on BBC One and later BBC News 24 and BBC World. The pips can be heard every hour on the BBC's worldwide radio station BBC World Service.

In the late 80s, 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 and Chris Evans' shows).

In the past, the pips had also been broadcast on the BBC Television Service though this 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, though this is usually done in jest and in actual fact happens rarely..

Although rare, in some instances the pips have been delayed with this happening on The Steve Wright in the Afternoon Show back in November 2001 where the pips were delayed by over half a minute in order for the music to continue playing [as the song was being paid for by a listener as it was part of the annual Children In Need Radio 2 marathon].

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

The pips are used elsewhere in the world, namely on Australian Broadcasting Corporation Radio. ABC Radio

In Hong Kong, similar pips are also used on RTHK 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 an hour (except in the late hours when the pips are broadcast every hour) immediately before the news headline reports.

History

The pips have been broadcast since 5 February, 1924, and were the idea of the Astronomer Royal Sir Frank Watson Dyson and 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 the pendulums. Two clocks were used in case of a breakdown. These sent a signal each second to the BBC, who converted them to the audible oscillatory signal that is broadcast.

The signal on the line was inverted; that is, 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 easily.

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.

External links

http://www.miketodd.net/other/gts.htm
http://news.bbc.co.uk/1/hi/sci/tech/271319.stm
http://www.radionetherlands.nl/features/media/practical/time.html
http://www.bbc.co.uk/radio4/today/reports/arts/rednose_ringtones_20050307.shtml
http://www.clockco.co.uk/article_info.php?articles_id=15

References