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I think our helmet-clad robot friends might have been making a little joke that we’ve apparently all missed. The BPM of Harder, Better, Faster, Stronger is actually 123.45.

How do I know this? It so happens that for over 10 years I’ve written an app called Tempi that shows the music BPM in real time, so I know a little bit about the science and algorithms behind music tempo detection.

Most tempo detection software works basically the same way:

• A specialized algorithm called the Fast Fourier Transform (FFT) collects overlapping energy levels at different frequency bands.
• Those levels are refined into well-defined peaks that represent rhythmic events in the track.
• Another algorithm (autocorrelation) looks for patterns, or more accurately periodicity, in those peaks.

But these patterns are tricky because there’s all kinds of noise, performance inaccuracies, and rhythmic harmonics throwing things off. All that is to say, a) it’s complicated and b) it’s not perfectly accurate.

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