It's a chirp obtained by running a gravity wave through a loudspeaker. It chirps because as the black holes spiral closer they spin faster sending out a higher frequency gravity wave. Starts off at 35 hz and gets to 250 hz prior to the collision. The two colliding black holes were 29 and 36 times the mass of the sun. That's a big collision!

This is the first confirmed gravity wave signal from the LIGO device.