Chord Finder from Audio

The file is turned into a chromagram — how much energy sits in each of the twelve pitch classes, frame by frame. Blocks of about half a second are averaged and compared with triad and seventh chord templates by cosine similarity. The best match becomes the chord for that block, adjacent blocks naming the same chord are merged, and single-block flickers between two readings of the same chord are dropped.

That method is honest about what it can hear. Pitch-class energy tells you which notes are sounding, not which one is lowest, so inversions and slash chords are out of reach. Chords a third apart share two of three notes, so a masked note can flip a reading to the relative major or minor. Distortion and drums add energy across the whole spectrum and blur everything.

Use it as a fast starting point on a stem, a loop or a sparse arrangement, then confirm the low-confidence rows by ear. Paste the result into the Chord Progression Analyzer to see which keys fit the sequence, or the Chord Transposer to move it.