Gravitational waves originating from the inspiral phase of compact binary systems, such as neutron stars or black holes, have the useful property that energy emitted as gravitational radiation comes exclusively from the orbital energy of the pair, and the resultant shrinking of their orbits is directly observable as an increase in the frequency of the emitted gravitational waves. To leading order, the rate of change of frequency f is given by d f d t = 96 π π 8 / 3 ( G M ) 5 3 f 11 3 5 c 5 , where G is the gravitational constant, c is the speed of light, and M is a single (therefore computable) number called the chirp mass of the system, a combination of the masses ( m 1 , m 2 ) of the two objects M = ( m 1 m 2 ) 3 / 5 ( m 1 + m 2 ) 1 / 5 . By observing the waveform, the chirp mass can be computed and thence the power (rate of energy emission) of the gravitational waves. Thus, such a gravitational wave source is a standard siren of known loudness.