Audio FilesThe binary black hole merger events that LIGO has detected are in the audio band. They can be converted to sound (.wav) files, so that you can hear them.
|Data: whitened, bandpassed|
|Data: Whitened, bandpassed, frequency shifted +400 Hz|
|Waveform template derived from GR, whitened|
|Waveform template derived from GR, whitened, frequency shifted +400 Hz|
Notes on audio files:
- Gravitational waves are not sound; for example, they travel at the speed of light, not the speed of sound.
- In a similar way, radio waves are not sound, and they also travel speed of light; but our radios have no problem converting that to sound.
- LIGO data has lots of noise at both low and high frequencies, so it's virtually impossible to hear the weak signals unless the data are first whitened and bandpassed to suppress the low- and high-frequency noise, leaving the quiet band between 40 Hz and 300 Hz untouched.
- We also whiten the waveform template derived from GR that best matches the data.
- The signals are at the low end of the audio band (below a few hundred Hz). They sound like faint thumps; it's hard to hear the "chirp". We can frequency-shift the data and the waveform template by +400 Hz, into the sweet spot of our hearing range; then we can hear the chirp better.
- All the signal processing details are in our binary black hole event tutorials; for example, for GW150914.