To an astonished audience, Nimtz announced that his team at Cologne had not only measured superluminal speeds for their microwaves, but had actually sent a signal faster than light. The signal in question was Mozart's 40th Symphony. What they did was frequency modulate their microwave source with the music and then measure how quickly the music arrived after traversing the forbidden zone in a waveguide. According to Nimtz, Mozart's 40th hopped across 12 centimetres of space at 4.7 times the speed of light. What's more, Nimtz actually had a recording to prove it. To his now bemused audience, he played a tape in which among the background hiss strains of Mozart could be heard. This was the "signal" that had travelled faster than light.