The first time Cage mentioned the idea of a piece composed entirely of silence was during a 1947 (or 1948) lecture at Vassar College, A Composer's Confessions. Cage told the audience that he had "several new desires", one of which was to compose a piece of uninterrupted silence and sell it to Muzak Co. It will be three or four-and-a-half minutes long—those being the standard lengths of "canned" music and its title will be Silent Prayer. It will open with a single idea which I will attempt to make as seductive as the color and shape and fragrance of a flower. The ending will approach imperceptibility.
In 1951, Cage visited the anechoic chamber at Harvard University. An anechoic chamber is a room designed in such a way that the walls, ceiling and floor absorb all sounds made in the room, rather than reflecting them as echoes. Such a chamber is also externally sound-proofed. Cage entered the chamber expecting to hear silence, but he wrote later, "I heard two sounds, one high and one low. When I described them to the engineer in charge, he informed me that the high one was my nervous system in operation, the low one my blood in circulation." Cage had gone to a place where he expected total silence, and yet heard sound. "Until I die there will be sounds. And they will continue following my death. One need not fear about the future of music." The realisation as he saw it of the impossibility of silence led to the composition of 4′33″.
In defining noise music and its value, Paul Hegarty in Noise/Music: A History (2007) contends that it is John Cage's composition 4'33" that represents the beginning of noise music proper. For Hegarty, noise music, as with 4'33", is that music made up of incidental sounds that represent perfectly the tension between "desirable" sound (properly played musical notes) and undesirable "noise" that make up all noise music.
"They missed the point. There’s no such thing as silence. What they thought was silence, because they didn’t know how to listen, was full of accidental sounds. You could hear the wind stirring outside during the first movement. During the second, raindrops began pattering the roof, and during the third the people themselves made all kinds of interesting sounds as they talked or walked out."
-John Cage sobre a estreia de 4'33" em 1952
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