Finding a song's BPM
Choose a file, read the tempo, then put it to use.
Your browser decodes up to a minute of the song, taken from across it, marks where each note and drum hit begins, and measures how evenly those onsets repeat. The steadiest period becomes the tempo, rounded to whole beats per minute. The key comes from the same pass.
Why half and double tempo show up
A track at 140 BPM often hits hardest on every other beat, which counts as 70, while busy hi-hats can count as 280. Both are steady pulses in the same song, so the page lists them too. Tap along with the chorus: the count that feels natural is the one to use.
Pair it with vocal removal
DJs line up an acapella with the next track by tempo and key; singers and drummers practice over the instrumental at the song's own speed. Remove the vocals to get both parts, or start from the acapella extractor if you only need the voice.