Greenwich Time Signal
The Greenwich Time Signal (GTS), popularly known as the pips, is a series of six short tones broadcast at one-second intervals by many BBC Radio stations. The pips were introduced in 1924 and have been generated by the BBC since 1990 to mark the precise start of each hour. Their utility in calibration is diminishing as digital broadcasting entails time lags.
The six pips
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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 kHz tone (about half way between musical B5 and C6), which, for the first five, last a tenth of a second, while the final pip lasts half a second. The actual moment when the hour changes – the "on-time marker" – is at the very beginning of the last pip.
When a leap second occurs (exactly one second before midnight UTC), 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 possibility of an extra pip for the leap second thus justifies the final pip being longer than the others, so that it is always clear which pip is on the hour. Before leap seconds were conceived, the final pip was the same length as the others. Although "negative" leap seconds can also be used to make the year shorter, this has never happened in practice. 
Although normally broadcast only on the hour by BBC domestic radio, BBC World Service use the signal at other times as well. The signal is generated at each quarter-hour and has on occasion been broadcast in error.
The pips are used by several stations, but not always at every hour. On Radio 4, the pips broadcast every hour, except when they are replaced at the start of the 6 pm and midnight news bulletins (and the start of the Westminster Hour on Sundays at 10 pm) by the Westminster chimes from the Elizabeth Tower (formerly the Clock Tower) at the Palace of Westminster, with the hour chimes of Big Ben, sometimes called the "bongs" (though these are more associated in the popular mind with ITV's News at Ten).
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.
The pips were used on Radio 1 during The Chris Moyles Show at 6.30 am just after the news, 9 am as part of the Tedious Link feature, 10 am (at the end of the show) and often before Newsbeat. As most stations only air the pips on the hour, the Chris Moyles show was the only show where the pips were broadcast on the half-hour. Masterpieces, the playing of an album in its entirety, is begun with pips, and they also feature at 7 pm on Fridays to signify the start of the weekend and at 4 pm on Sundays to mark the start of The Official Chart Show. The pips are also used at 7 pm on Saturday evenings at the start of Radio 1's 12-hour simulcast with digital station BBC Radio 1Xtra.
The pips are used on Radio 2 at 7 am and 8 am during The Chris Evans Breakfast Show, at 5 pm between Steve Wright's and Simon Mayo's Drivetime show and at 7 pm at the end of the show. They are also broadcast during Anneka Rice's show at 7 am and 8 am on a Saturday and at 8 am and 9 am on a Sunday during Clare Balding's show. Radio 2's coverage of the Eurovision Song Contest is preceded by the pips.
The BBC does not allow the pips to be broadcast except as a time signal. Radio plays and comedies which have fictional news programmes use various methods to avoid playing the full six pips, ranging from simply fading in the pips to a version played on On the Hour in which the sound was made into a small tune between the pips. The News Quiz also featured a special Christmas pantomime edition where the pips went missing, and the problem was avoided there by only playing individual pips and not the whole set. The 2012 project Radio Reunited, however, did use the pips not as a time signal, but simply to commemorate 90 years of BBC Radio.
The pips for national radio stations and some local radio stations are timed relative to UTC, from an atomic clock in the basement of Broadcasting House 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 accurately received on long wave as far as 160 kilometres (100 mi) from the Droitwich AM transmitter, which is the distance to Central London.
As a pre-IRIG and pre-NTP time transfer and transmission system, the pips have been a great technological success. In modern times, however, time can be transferred to systems with CPUs and operating systems by using BCD or some Unix Time variant.
Newer digital broadcasting methods have introduced even greater problems for the accuracy of use of the pips. 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.
DVB, DAB (Eureka 147 and Digital Radio Mondiale) and FM Radio Data System all support separate time signal transmission subsystems with accuracy equal to or several orders of magnitude better than the pips, so the listener need not worry about decoding the pips to synchronize the clocks on these systems.
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 pendula. Two clocks were used in case of a breakdown of one. These sent a signal each second to the BBC, which converted them to the audible oscillatory tone broadcast.
The Royal Greenwich Observatory moved to Herstmonceux Castle in 1957 and the GTS equipment followed a few years later in the form of an electronic clock. Reliability was improved by renting two lines for the service between Herstmonceux and the BBC, with a changeover between the two at Broadcasting House if the main line become disconnected.
The tone sent on the lines was inverted: the signal sent to the BBC was a steady 1 kHz tone when no pip was required, and no tone when a pip should be sounded. This let faults on the line be detected immediately by automated monitoring for loss of audio.
The pips were also broadcast by the BBC Television Service, but this practice was discontinued by the 1960s.
Crashing the pips
The BBC discourages any other sound being broadcast at the same time as the pips; doing so is commonly known as 'crashing the pips'. This was most often referred to on Terry Wogan's show, Wake Up to Wogan, although usually only in jest since the actual event happened rarely. Different BBC Radio stations approach this issue differently. Both BBC Radio 1 and Radio 2 generally take a more laid-back approach with the pips, usually playing them over the closing seconds of a currently playing song or a jingle 'bed' (background music from a jingle), followed by their respective news jingles. Many BBC local radio stations also play the pips over the station's jingle. BBC Radio 4 is stricter. It is an almost entirely speech-based network; incidents at the end of the Today programme regularly cause listeners' complaints.
In the late 1980s Radio 1 featured the pips played over a station jingle during Jakki Brambles' early show and Simon Mayo's breakfast show. This was not strictly crashing the pips as they were not intended to be, or mistaken for, an accurate time signal.
At 8 am on 17 September 2008, to the surprise of John Humphrys, the day's main presenter on the Today programme, and Johnnie Walker, who was standing in for Terry Wogan on Radio 2, the pips went adrift by 6 seconds, and broadcast seven pips rather than six. This was traced to a problem with the pip generator, which was 'repaired' by switching it off and on again. Part of Humphrys' surprise was probably because of his deliberate avoidance of crashing the pips with the help of an accurate clock in the studio.
A sudden total failure in the generation of the audio pulses that constitute the pips was experienced on 31 May 2011 and silence was unexpectedly broadcast in place of the 17:00 signal. The problem was traced to the power supply of the equipment which converts the signal from the atomic clocks into an audible signal. Whilst repairs were underway the BBC elected to broadcast a "dignified silence" in place of the pips at 19:00. By 19:45 the same day the power supply was repaired and the 20:00 pips were broadcast as normal.
Similar time signals elsewhere
Many radio broadcasters around the world use the Greenwich Time Signal as a means to mark the start of the hour. The pips are both used in domestic and international commercial and public broadcasting. Many radio stations use six tones similar to those used by the BBC World Service; some shorten it to five, four, or three tones.
- Australia - pips are used on ABC Radio National and ABC Local Radio at the top of every hour, as well as on Fairfax Media talkback stations- 2UE, 3AW, 4BC and 6PR.
- Hong Kong - 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 during the day and on the hour at night, immediately before the news headline reports.
- Finland - on YLE's radio services the pips are broadcast on the hour.
- Netherlands - only three pips are used. There used to be six, however it was felt that people would lose count, so now only three are used.
- Spain - the signal is broadcast by almost all radio stations, even by music stations, but depends on the frequency: music stations usually use pips on the hour, but most of the non-musical stations broadcast the signal every 30 minutes. Los 40 Principales, the most important music radio in Spain, broadcast a different version of GTS: two first pips sound and then a music is added on the background, using the rhythm to create the corporative jingle of the radio. Other musical radios like Máxima FM and M80 Radio, both owned by PRISA, and Europa FM use a similar effect.
- Catalonia, Spain - dance music station Flaix FM and Hot AC station Ràdio Flaixbac, both owned by the same media group, broadcast every half-hour a very short sequence of two very short tones followed by a longer one, the whole lasting not more than one and a half seconds. Els 40 Principals, the Catalan edition of Spanish radio Los 40 Principales, use the same jingle, using a mix of GTS and corporative music.
- Malaysia - RTM radio stations use the pips hourly before the news broadcast but only the top-of-the-hour pip is sounded. Until late 2012, the time signal is simply a short pip on the 59th second before the hour and a longer pip on the top of the hour. In a news report in The Star on 1 January 1982, the pips were used to sound similar to the BBC's.
- Ireland - six pips are broadcast before news bulletins at 07:00, 13:00 and 24:00 on RTÉ Radio 1.
- Hungary - the national radio channel Kossuth broadcasts five stereophonic pips at the top of every hour, the fifth being longer than the others.
- Canada - the National Research Council Time Signal is broadcast daily on Ici Radio-Canada Première at 12:00 EST and on CBC Radio One at 13:00 EST. It is Canada's longest running radio feature and has been broadcast every day since November 5, 1939.
- United States - the pips can be heard on the Middlebury College radio station WRMC.
- North Korea - the pips are heard on Voice of Korea before its startup at 17:00.
- New Zealand - the equivalent of BBC Radio 4, Radio New Zealand National, plays the six pips at the top of every hour.
- Argentina - all news/talk stations (Radio Nacional, Radio Mitre, Radio Continental, Radio 10, Cadena 3, etc.) air the six pips similar to the BBC every hour, and 3 pips for every half-hour similar to Catalonia.
- France - the station France Inter broadcasts four very short pips every hour, which are almost invariably crashed. The last pip, which is as long as the other ones, marks the top of the hour. Some local stations of the France Bleu network also air four pips that are a little longer than Inter's.
- Belgium - Both RTBF and VRT broadcast six short peeps every hour.
- Germany - the Canadian Forces Network broadcasts a time signal before the hourly news bulletins from CBC. Every hour the German Deutschlandfunk broadcasts four beeps, the last one being longer than the others; between 05:00 and 18:00 on weekdays they are broadcast every half-hour and often omitted at 21:00 when there is no news programme scheduled. Similarly, Deutschlandradio Kultur uses six pips, the last one being longer than the others.
- Switzerland - The first channel of the Swiss radio used to play three short peeps, the third being higher than the others. It seems to have disappeared now.
- Israel - Kol Israel hourly newscasts begins with six tones
- former Yugoslavia- JRT broadcast the six pips before the news (on the hour) on radio as well as on television, before the start of the TV Dnevnik at 08:00 pm. The broadcast on TV was stopped in 1974 because the TV Dnevnik was moved to its current term at the bottom of the hour (07:30 pm)
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- Scientific pitch notation
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