Friedrich Wilhelm Opelt (1794–1863) proposed a revolutionary music theory based on the recursive features of human hearing. Opelt based his theory on a recent invention, Charles Cagniard de la Tour’s mechanical siren (1819), which he expanded and improved. Cagniard’s model consists of a metal disk with holes in regular intervals that, when set in rotation and with air blown through them, produce a series of air puffs. Once their pulsation increases above 20Hz, this pulse is heard as a continuous, rising pitch. Opelt employed this device to test the properties of hearing against the parameters of music: he noted that more complex patterns of holes translate into intervals, chords, and harmonies and showed that every pitch event can be translated into a corresponding rhythmic event. Pitch and rhythm may be different perceptual parameters, but physically, they are both temporal events, which merely inhabit different dimensions of the time axis.