Leap second

Live recording of time signal station CHU, Canada, on 30 June 2015 beginning at exactly 23:55:00 UTC on a frequency of 7850 kHz. The recording last exactly 10 minutes and 1 second, ending at 0:10:00 UTC. A leap second occurs at 23:59:60 UTC. This can be noted by the 1 second of silence between the 5m:00s mark in the recording (23:59:60 UTC) and the 5m:01s mark (0:00:00 UTC) denoted by the start of the one-second-long tone. This is followed by 9 seconds of silence. Before the leap second, the forecast difference between UT1 and UTC (DUT1 = UT1 minus UTC) to a precision of one tenth of a second was -0.7 seconds. This is indicated by CHU by using a sequence of double tones at 9 seconds through 15 seconds after the start of each minute except for the minute beginning an hour. Following the leap second, DUT1 is +0.3 seconds, marked by double tones at 2 seconds through 4 seconds after the start of the minute, again, except for the minute beginning an hour. 

Recorded by Richard Langley, courtesy of the Shortwave Radio Archive.

Part of the Shortwave Transmissions project, documenting and reimagining the sounds of shortwave radio - find out more and see the whole project at https://citiesandmemory.com/shortwave