John Cage, Experimental Music, 1958

"For certain engineering purposes, it is desirable to have as silent a situation as possible. Such a room is called an anechoic chamber, its six walls made of a special material, a room without echoes. I entered one at Harvard University several years ago and 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 was my blood in circulation."

from "Chance" Whitechapel Gallery Press