This paper is an attempt to understand music theory from the perspective of written and sounding media. We will examine three radically different music-theoretical practices, which operate with different forms of written notation, different musical instruments, and with surprisingly different purposes in mind: the monochord-based theory of Franchises Gaffurius (1518), the siren-based theory of Wilhelm Opelt (1834), and the piano-and-score based theory commonly practiced in our age.