BPM Detector

Detect the BPM of a song from its audio file

The BPM Detector measures the tempo of a song file in beats per minute. Drop in an MP3, WAV, M4A, OGG or FLAC track and it shows the BPM, a confidence score, the half-time and double-time readings and a marker on every beat it found, drawn on the waveform. Turn on the click track and press play to hear the detected beat on top of the music.

DJs use it to label a crate before a set, producers to set the project tempo for a sample or remix, video editors to cut on the beat, and runners and dance teachers to sort playlists by pace. Drop a whole folder at once: each song gets a row in the batch table, and the results download as a CSV file for a spreadsheet or DJ library.

All analysis runs in your browser — the songs are never uploaded.

How to use the BPM Detector

1. Drop one or more songs onto the box, or click it to choose files.
2. Wait for the progress bar; each song takes a few seconds. Cancel stops a long batch.
3. Read the BPM, the exact tempo to one decimal and the confidence. If the number feels twice too fast or slow, choose a Tempo range.
4. Zoom the waveform to 10 or 30 seconds to inspect the beat markers, then tick Play a click on every detected beat and press play.
5. For a batch, use Show to open any song and Download CSV to save every result.

BPM Detector features

How the tempo is detected

1. Onset envelope. The audio is mixed to mono, resampled to about 11 kHz and cut into 46 ms windows every 5 ms. For each window the tool measures how much louder each frequency band became since the previous window (log-compressed spectral flux). Drum hits and note attacks show up as sharp peaks.
2. Periodicity. The autocorrelation of that envelope, summed at one to four beat periods (a comb filter), reveals which spacings between peaks repeat. The strongest candidates between 40 and 240 BPM are kept.
3. Half or double? For each candidate the envelope is folded at that period in 8-second windows; a real beat makes the folded peaks line up sharply. A gentle preference for tempos around 120 BPM, where listeners most often place the beat, decides between tempos that fit equally well.
4. Beat tracking. Dynamic programming (Ellis, 2007) picks the sequence of beats that best follows the onsets while keeping a steady spacing. A least-squares fit through those beat times gives the exact BPM.

When the result is wrong — and how to fix it

• Half or double tempo is the most common difference from a published BPM: a 170 BPM drum & bass track can also be counted as 85, and a 70 BPM ballad as 140. Choose the tempo range that matches the genre.
• Tempo changes and live drummers: the tool reports the main tempo of the analysed audio; beat markers follow gradual drift, but a song with a big tempo change is best cut into parts with the Audio Cutter.
• Ambient, classical and spoken audio with few clear attacks gives a low confidence. Tap along with the BPM Tapper instead, then practise with the Metronome.
• Songs longer than 15 minutes (DJ mixes) are analysed over their first 15 minutes.