Because these are massive objects, the chirp evolves more rapidly and lasts less time in the LIGO band than is the case with neutron stars. For the 15 Mpc example, you can still see the signal in the spectrum although it is not possible for the ear to detect it in the sound track. Please note to the this engineering run was a single arm test and that the sensitivity was much lower than a full interferometer can give. A process that results in a varying or time dependent signal can be characterized by its frequency spectrum. For example a pure harmonic tone such as a sine wave signal corresponds to a frequency spectrum with a single peak at the frequency characterizing that tone.
Most physical processes generate signals at many different frequencies simultaneously.
These are not astrophysical in nature and must be accounted for in the signal processing techniques that are designed to detect weak signals of interest embedded in our detector's noise. On the other hand the components of the simulated astrophyiscal signal are easily discernible above the background when the signal strength is sufficiently high. Physicists study gravitational waveforms in this manner.