Song key finder
Drop a track and read its key. The chord progression comes with it, which is usually the fastest way to confirm the key is right.
How the key is worked out
The key comes from the same chromagram used for chord detection. Averaging pitch-class energy over the whole track produces a profile of how much each of the twelve notes is used, and that profile is compared against the 24 key profiles from the Krumhansl-Schmuckler experiments, which measured how strongly listeners associate each note with each key.
The best-matching key wins, and the confidence comes from how far ahead of the runner-up it is. A track that fits two keys almost equally well is genuinely ambiguous, not a failure of the measurement.
Relative keys and modulation
C major and A minor contain the same seven notes, so no method that counts pitch classes can fully separate them. What separates them is emphasis: which chord the music keeps returning to. If the reported key looks wrong, glance at the chord timeline - the chord that starts and ends sections is usually the tonic.
Only one key is reported for the whole track. A song that modulates for the last chorus gets the key it spends most of its time in, and the chord timeline is where you will see the change.
Questions
- Why does it say A minor when I hear C major?
- Those two keys use the same notes, so pitch-class evidence alone cannot separate them. Look at which chord the sections resolve to on the timeline; that is your tonic.
- Does it detect modes like Dorian or Mixolydian?
- Not as such. Modal music is reported as the major or minor key with the closest note content, which for a Mixolydian song is usually the major key a fifth below.