Chordec does chord recognition for songs from your iOS device. It was originally developed by Weibin Shen and is now re-released. Its algorithm has the highest accuracy among published algorithms till at least the end of 2012.
Chord recognition accuracy under default Sensitivity value:
82% if counting only major and minor chords,
65% if counting only maj, min, aug, dim, 7, maj7 and min7
Chordec features a Sensitivity slider. It can change the sensitivity of the chord recognition model. Although the default value of this slider can return meaningful chord estimation results for majorities of the music out there, for some music, tweaking this value may return a better chord recognition result.
Special Thanks To:
Georgia Tech Center for Music Technology (GTCMT)
International Society for Music Information Retrieval (ISMIR)