Sound is a wave and a wave has a time period. A note consists of a fundamental (which determines its pitch) and a series of harmonics (or overtones) with frequencies that are integer multiples of the fundamental. If you record a note and slow it down a lot, it will eventually appear as a series of discreet pulses. "Hora Harmonica," realized in 1983, is not a piece of music, but conceptual art inspired by the physics of sound. Albert Mayr proposes a harmonic clock, a model of non-linear time. Imagine a note that has a fundamental with a period of exactly 60 minutes. Its first overtone would "ring" at 30 and 60 minutes; its second at 20, 40, and 60; its third at 15, 30, 45, and 60; and on and on. Mayr created such a "virtual" note (i.e., this is not a note slowed down, but digitally re-created for practical audibility purposes), placing in the period of one hour its harmonics up to the 12th. The full "sound" sounds at the very beginning of the track. Then the listener waits for five minutes before something else (the 12th harmonic) is heard again. The 11th appears alone at five minutes and 27 seconds, the tenth at six minutes, the ninth at six minutes and 40 seconds -- a chart details the action (or lack of) in the booklet. Besides suggesting a different way to keep track of time, in which one would eventually recognize five-, six-, ten-, and 12-minute periods by the sound of their respective harmonic, Mayr's piece doesn't fertilize much ground for philosophical thought. But his realization of the concept is exemplary and the 16-page booklet is generous in historical and conceptual background.