What is Beat Detector / BPM Counter?

The Beat Detector finds the tempo of audio in beats per minute (BPM) and also estimates the musical key on uploaded files. It picks up energy peaks in the waveform through the Web Audio API to pinpoint rhythmic patterns. You can analyze a file, listen live through the microphone, or tap along to any beat manually for a quick BPM reading.

Three detection modes share the same readout. File analysis decodes the audio with the Web Audio API, scans for onset peaks across 40-220 BPM to find the dominant tempo, then runs a chroma analysis with Krumhansl-Schmuckler key profiles to estimate the musical key (e.g. A minor, C major). Live mic captures audio from your microphone and refreshes the BPM in real time as it locks onto a steady beat. Tap tempo averages your last several taps, so you can clock a song playing on the radio with no upload required.

How to use

1. Upload an audio file (MP3, WAV, OGG), start the live mic to detect the beat in real time, or use the tap-tempo button to manually tap along to music playing nearby.
2. For uploaded files, the detector scans the audio waveform for energy peaks, calculates the dominant tempo, and estimates the musical key from a chroma analysis.
3. View the detected BPM with a confidence indicator and key readout, then copy the result or try another track.

When to use

• DJ prep — knowing track BPMs in advance to plan transitions and key matches.
• Setting a metronome at the right tempo when learning a new song on guitar or drums.
• Choosing music that matches a target running cadence (often 160-180 BPM).

Result

You're a DJ preparing a set and need to match tempos. Upload each track to instantly see its BPM — a house track reads 128 BPM, a drum & bass track reads 174 BPM.

FAQ

How accurate is the automatic BPM detection?

On tracks with a steady kick drum or strong bass line, expect accuracy within ±1 BPM. Songs with rubato, complex polyrhythms, sparse percussion, or heavy reverb can throw the detector off by 5-10 BPM, and the tool may flag low confidence on those.

Why does the detector sometimes report half or double the real tempo?

It's locking onto a different beat layer — picking up every other kick instead of all of them, or counting hi-hats instead. If the result feels wrong, double or halve the number and check whether the new figure matches what you tap with the tap-tempo button.

What audio formats can I upload?

MP3, WAV, OGG, M4A, FLAC, and AAC all work because the Web Audio API decodes them natively. Very long files (over 10 minutes) may take a couple of seconds to decode, but detection itself is near-instant once the buffer is ready.

How many taps does the tap tempo need before it gives a result?

Two taps produce a first estimate, but accuracy keeps improving up to about eight taps as the rolling average smooths out timing wobble. Tap on the strong beat (the kick or the downbeat) rather than every snare hit for the cleanest result.

What does the confidence value actually mean?

It reflects how clearly a single tempo dominated the beat-spacing histogram. High confidence means one BPM appeared in nearly every interval the detector measured. Low confidence usually means tempo changes mid-song, or two layers competing for dominance.

Related Tools