detect song BPM online
Detection sums the energy of three frequency bands (bass, mid and treble) into a novelty signal, then finds that signal's dominant periodicity through autocorrelation, inside a default range of 40 to 240 BPM. Instead of returning just one number, the result includes a confidence score and a half-time or double-time alternate, because the most common error in automatic BPM detection is locking onto the wrong octave.
The 64 BPM alternate is the automatically computed half-time, useful for anyone who prefers organizing the playlist at a slower tempo.
The 181.8 BPM candidate had higher salience (0.947 versus 0.931), but lost to 89.5 in octave resolution.
With no periodic energy to lock onto, the tool returns an explicit empty result, instead of risking a random guess.
BPM (Beats Per Minute) is the unit of measurement for musical tempo, how many beats occur per minute. 120 BPM means 2 beats per second. It is fundamental for syncing loops in music production, aligning video cuts to music, configuring delay and arpeggiators in synthesizers, and beatmatching in DJing.
It is octave ambiguity: strong off-beat hits can generate a double-time candidate that scores higher on raw salience than the real tempo. In a test with a 90 BPM track, the 181.8 BPM candidate scored higher (0.947 versus 0.931), yet the tool still chose 89.5 as the primary answer, keeping 181.8 as the alternate.
Three bands at different weights: 20 to 180Hz (weight 1.3, bass and kick), 180 to 4200Hz (weight 1.0, snare and vocals), and 4200 to 11000Hz (weight 0.65, hi-hats and cymbals). Summing all three instead of just one avoids missing the beat in songs where the bass is weak but the treble is strongly marked.
It means a second BPM candidate scores nearly as strongly as the chosen one, usually an octave above or below. It does not mean the BPM is wrong: on an ambiguous 90 BPM track confidence landed at 47%, even with a correct final value, because the 181.8 BPM candidate had a close salience score.
The analysis runs entirely in your browser (in a Web Worker). No file is uploaded to any server.