iOS Universal Music
What Key is a key detection app that determines the musical key of a song in real time. Using the pitch detection algorithm from Pitch to Note, What Key matches the notes being played to major, minor, blues, bebop (jazz) and other scales in all keys, picking the scale and key with the best match.
What Key is a universal app that runs on iPod Touch, iPhone, and iPad.
What Key works best on music with minimal percussion tuned to A4=440 Hz.
Updated for newer devices.