When massive bodies (black holes or neutron stars) orbit each other, they emit gravitational waves at twice their orbital frequency. Since the gravitational waves carry energy away from the system, the distance between bodies decreases due to the conversation of energy. Since the distance has decreased, the bodies must orbit each other faster. Hence the emitted gravitational wave signal increases in frequency, and is known as a chirp. This period of inspiralling is known as the inspiral phase. Eventually the distance between the bodies reaches a minimum, with maximum orbital frequency. Beyond this point, the masses plunge towards each other and form a single body (known as the merger phase). This new single body is expected to vibrate to its own internal modes for a short period of time. This period is known as the ringdown phase.
The range of frequencies emitted during the inspiral phase depends on the
masses of the bodies. For low mass bodies e.g those with 1-5 times the mass
of the Sun, the resulting chirp increase quickly up to about 1500Hz. This
is within the range of human hearing, ~40-1500Hz.
The mp3's on the right are designed to give an idea of what a gravitational
wave observer would hear, if the detector output were converted to the audio
spectrum. In it you should be able to hear a variety of very distinctive
chirps, that increase in frequency (or pitch) until they reach a maximum.
Later in the mp3 are some expected ringdown's, which have rapidly decaying
amplitude profiles. Also near the very end is a constant frequency, or tone,
which could be heard from a 'neutron star quake'. However in reality, the
gravitational wave detector is subject to all sorts of noise sources, and
the actual signal can become very corrupted. Indeed, the main job of a gravitational
wave data analyst is to remove the noise! The second mp3 is designed to
give an idea of the signal within the noise.