Greenwich Time Signal 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
Time reversal signal processing time reversal (using a negative time) of that solution is also a solution. This occurs because the standard wave equation only contains even order derivatives. Some media are not reciprocal (e.g. very lossy or noisy media), but many very useful ones are approximately so, including sound waves in water or air, ultrasonic waves in human bodies, and electromagnetic waves in free space. The medium must also be approximately linear. Time reversal techniques can be modeled as a matched filter. If a delta function is the original signal, then the received signal at the TRM is the impulse response of the