The Pips (Greenwich Time Signal)
To mark the start of the hour, the BBC broadcasts a series of 6 tones officially known as the Greenwich Time Signal or more commonly "The Pips". The first 5 tones last 0.1 seconds and mark the 5 seconds preceding a new hour. The last tone is 0.5 seconds long and begins precisely on the stroke of the new hour. All the tones are sine waves at a frequency of 1000Hz.
In these days of digital radio, the times taken to process signals can vary significantly across equipment meaning precise timing using the Pips is almost impossible. Nevertheless, they continue to be broadcast (though not on every hour) and remain an ubiquitous part of BBC radio.
You can listen to and download the Pips below using our soundcloud widget.