How a tempo is found
In two steps that are easy to run together and wrong to. First the recording is reduced to an onset curve — a line that rises wherever something new is struck and ignores everything that is merely continuing. Only then is that curve searched for a repeating period. Looking for a period in the waveform itself finds the pitch instead, which is why a naive attempt reports a bass note as the tempo.
Forty seconds from the middle of the track is enough. Intros and fade-outs are where the beat is least reliable, and the answer has settled long before the song has.
Why half and double time are the usual mistake
A bar repeats just as reliably as a beat does, so the tempo and half the tempo both look like strong candidates — which is why so many detectors report 87 for a 174 bpm track. Nothing about the audio says which is the beat and which is the bar; that is a musical judgement rather than a measurement.
So the ÷2 and ×2 buttons are next to the number, and the tool says when it is unsure rather than pretending. If the result feels like it is at the wrong level, it probably is, and one press fixes it.
Tapping, and when it is the better answer
Some music has no steady tempo to find: rubato piano, free jazz, ambient, anything recorded without a click. The tool says so instead of producing a number, because a confident wrong answer is worse than none.
Tap along and the tempo comes from the gaps between your taps — the median gap, so one clumsy press does not move the result. Leave it a couple of seconds and it starts counting again, which is what you want after losing the beat.
Frequently asked questions
The number is half what I expected.
That is the classic ambiguity: a bar repeats as convincingly as a beat, so both look right to any detector. Press ×2. The tool warns when its answer is not clear-cut, and that is exactly when to check.
Why does it say no beat was found?
Because there is nothing repeating to find. Free-tempo piano, ambient, spoken word and anything recorded without a click genuinely have no BPM — tapping along is the honest way to get a number for those.
How accurate is it?
Within a fraction of a beat on anything with a clear pulse. Live recordings drift by a beat or two over a song, so the figure is an average rather than a value that holds at every bar.
Does it find the musical key too?
No. Key detection is a different problem and much less reliable on a full mix; a number that is wrong a third of the time is not worth putting next to one that is usually right.
Is my music uploaded?
No. It is decoded and analysed in your browser and never sent anywhere.
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