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BPM Detector
Analyses an audio file and detects its tempo by autocorrelating the onset energy, with the runner-up candidates shown.
Video & Audio
Nothing uploaded
No sign-up
Free, unlimited
Drop an audio filedecoded and analysed in this page — nothing is uploaded
Add a file to begin.
In short
Tempo detection works by building an onset envelope — how sharply the energy rises from one short frame to the next — and then autocorrelating it to find the lag at which the pattern agrees with itself. That lag is the beat period. The limitation is mathematical rather than technical: half and double tempo fit the same pattern equally well, so no autocorrelation can tell 87 BPM from 174, and the choice between them is musical. Drum and bass is written as 174 rather than 87 and house as 128 rather than 64, so a detected figure that is exactly half or double what you expected is almost always that.
How to use the BPM Detector
- Drop the audio file in.
- Narrow the range if you already know roughly what to expect.
- Check the candidate table, not just the top figure.
About the BPM Detector
The BPM Detector analyses an audio file and detects its tempo by autocorrelating the onset energy, with the runner-up candidates shown. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.
What people use it for
- Finding the tempo of a track before importing it.
- Checking whether a recording drifted.
- Getting a starting BPM for a remix.
Details
| Method | Onset envelope, then autocorrelation |
|---|---|
| Frame | 10 ms |
| Ambiguity | Half and double fit equally — always shown together |
| Needs | A few seconds of steady pulse |
The candidate table is worth more than the headline number when a track is difficult. Two candidates within a few percent of each other means the detection is genuinely uncertain rather than confidently wrong, and a musician can usually pick correctly from the shortlist.
Where this tool stops
Assumes a steady tempo throughout. Live recordings, tempo changes and rubato produce an average that describes no part of the track.
Frequently asked questions
Why does it give me half the tempo I expected?
Because half and double are the same rhythm to an autocorrelation — a pulse every 345 ms fits a 174 BPM pattern and an 87 BPM one perfectly. Nothing in the audio distinguishes them; the answer is a musical convention. Both figures are always shown for that reason.
Why is my track undetectable?
Detection needs a repeating attack. Ambient music, solo strings, spoken word and anything with rubato give an onset envelope with no periodicity, so the best candidate is barely stronger than the rest — which is what the confidence figure reports.
Should I trim the intro first?
It usually helps. A long ambient introduction contributes onsets that belong to no tempo and dilutes the correlation. Analysing a representative thirty seconds from the middle gives a cleaner answer than the whole track.
Is the BPM Detector free, or is there a paid tier?
Free, unlimited, and no email address required. You can use it a hundred times a day and nothing changes.
Is my data uploaded anywhere?
No. The BPM Detector runs entirely in your browser using JavaScript. Nothing is transmitted, logged or stored, which you can verify yourself in the Network tab of your browser's developer tools.
What problem does the BPM Detector solve?
The jobs it is built for: finding the tempo of a track before importing it. Checking whether a recording drifted. Getting a starting BPM for a remix. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
When is the BPM Detector not the right tool?
Assumes a steady tempo throughout. Live recordings, tempo changes and rubato produce an average that describes no part of the track. Knowing where a tool stops being trustworthy matters more than the cases where it works.
Which values should I know?
Method is Onset envelope, then autocorrelation. Frame is 10 ms. Ambiguity is Half and double fit equally — always shown together. These are printed on the page itself, so you do not have to take them on trust.
Is there a file size limit?
There is no limit set by us, because your file is never uploaded — the only ceiling is the memory your own browser will give the tab. Very large files simply take longer to process, and a phone will give up sooner than a desktop.
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