Choose (or drag in) an audio file your browser can decode: If that doesn't start the music, hit Play . If the thing seems to be detecting spurious beats, tweak this threshold slider: You can also go wild and tune the adjustment speed: Or the smoothing factor for detection: If you really need to, you can also set the target BPM: If everything seems out of whack, you can: reset the playback rate, reset the smoothed BPM, or reset the beat detection ring buffers... An @akx joint. Open source.