gizmobench

BPM detector

Drop in an MP3, WAV, M4A, OGG or FLAC and this reads its tempo without the file leaving your tab: the browser decodes it, the tool builds an onset envelope from the audio and autocorrelates it, and the strongest steady pulse between 40 and 220 BPM comes back with a score. What it also shows is the part other detectors hide. A pulse matches itself just as well at half its rate and at twice it, so the half-time and double-time candidates are listed with their own scores rather than quietly discarded, and a confidence figure says how far the winner stands above the best tempo that is not one of its own octaves. If the estimate reads the song the other way round, tap along with the Tap button or type the tempo in, and the beat markers move with it. Up to 50 MB a file, and up to 60 seconds of it analysed at a time.

Open an audio file

· or drop a file anywhere on the stage. It is decoded here and never sent anywhere.

Never uploadedNo accountUp to 50 MB40 to 220 BPM
Estimate
not measured yet
Confidence
not measured yet
Candidates
not measured yet
Analysed
nothing yet

Ready. Choose an audio file, or drop one on the stage.

  • Tempowhat the tool concluded, and from how much audio
    No tempo measured yet.
  • Half and doublethe same pulse counted the other way, with its score
    Open a file to see the half-time and double-time candidates.
  • Beat markersseconds from the start of the section analysed
    Open a file to place the beats.
Why there is a list and not one number. A steady pulse matches itself just as well at half its rate and at twice it, so an algorithm that answers 140 and one that answers 70 are usually reading the same song. This tool scores the strongest pulse between 40 and 220 BPM, leans towards tempos near 120 the way a listener does, and then shows the half and the double with their own scores instead of hiding the choice it made. If it picked the wrong one, tap along with the Tap button or type the number in the Your tempo box: both replace the estimate, and the beat markers move with it.

What the readings mean

Confidence is one specific thing: how far the winning tempo stands above the best tempo that is not one of its own octaves. A half-time reading never counts against it, because that is not a disagreement about the beat. An unrelated tempo scoring alongside the winner does, and that is the file worth tapping along to. The beat markers are placed by finding the phase that lines up best with the onsets, so they are as steady as the performance is: a track played to a click lands on them, and a band that drifts will not.

Accuracy. An estimate, not a reading from the session file. It scores the strongest steady pulse and lists the half-time and double-time candidates beside it, because those are genuinely ambiguous in most music. Tap along or type the number to correct it. Nothing is uploaded: the file is decoded in this tab and dropped when you leave the page, and at most 60 seconds of it are analysed at a time.

Common questions

Is my audio uploaded anywhere?
No, nothing is uploaded. The file is decoded by your own browser in the page you are looking at, the analysis runs on the samples in memory, and nothing is sent to a server at any point. There is no account and no queue, and closing the tab is all it takes to be rid of the file.
Why does it show half-time and double-time instead of one number?
Because a steady pulse correlates with itself just as well at half its rate and at twice it, which is why one detector says 140 and another says 70 about the same track. The tool leans towards tempos near 120, the way a listener does, then shows you the half and the double with the scores they actually earned, so you can see the choice rather than inherit it.
What does the confidence figure mean?
It is how far the winning tempo stands above the best tempo that is not one of its own octaves. A half-time reading never counts against it, because that is not a disagreement about the beat. Strong means one tempo scored well clear of every unrelated rival, weak means more than one unrelated tempo fits and tapping along is the fastest way to settle it.
The number is wrong. Can I correct it?
Yes, two ways. Press Tap on each beat and the tempo those taps describe goes straight into the Your tempo box, which is exact arithmetic on your taps rather than an estimate. Or type the number yourself, between 40 and 220 BPM. Either one replaces the estimate on screen, and the beat markers are re-placed around the tempo you gave.
How much of the file does it listen to?
Up to 60 seconds, starting at the beginning unless you type a start and an end. When your section is longer than that the readout says so rather than trimming it quietly. A tempo is measured from a stretch of steady pulse, so a chorus is usually a better section to point it at than a fade-in.
What are the limits, and what will it refuse?
Files up to 50 MB, in any format your browser can already play, and sections of at least 4 seconds. Silence, an empty file, a format the browser cannot decode, a section too short to hold the slowest tempo twice, and a stretch where nothing starts at all, a held note or room noise, all come back as a message naming what happened and what to change, never as a number that was guessed.
Does it detect the key as well?
No. This measures tempo only: an onset envelope, an autocorrelation and the candidates that came out of it. Nothing here reads a key, a time signature or anything written in the session file the track came from.

An estimate, not a reading from the session file. It scores the strongest steady pulse and lists the half-time and double-time candidates beside it, because those are genuinely ambiguous in most music. Tap along or type the number to correct it.