What is Musical Key?
Also called: key, tonality
The key of a song is its home note and the scale built on it, such as C major or A minor. It tells you which notes and chords sound settled in the song and where the music wants to return.
Western music uses 24 major and minor keys: one major and one minor on each of the 12 notes. Major keys are often described as brighter and minor keys as darker, though the feel depends on much more than the key alone.
Knowing the key is useful in many situations: writing a melody or bass line that fits, choosing samples that work together, transposing a song for a singer, or picking tracks that blend in a DJ set.
Songs can change key partway through, called modulation, and some music is ambiguous enough that two keys are both reasonable answers, especially relative major and minor keys that share the same notes.
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Detect Key and BPM