C

C is the foundation of Western music theory — the C major scale uses all white keys on the piano with no sharps or flats, making it the first scale most musicians learn. C major sounds plain, clear, and open — the neutral ground every other key is measured against — while C minor is stormy and serious, the key of Beethoven's Fifth.

Middle C (C4, 261.63 Hz) is the anchor point of standard musical notation, sitting on the ledger line between the treble and bass clefs. The key of C major has been called the "people's key" for its accessibility.