williams mix / john cage

I don't really know the historical context, but I feel safe in assuming it was relatively mind-blowing for 1951. From http://sfsound.org/tape/CageAustin.html:

The process of creating the original realization of Williams Mix, as Cage explained, involved the precise cutting/splicing of recorded sounds to create eight separate reel-to-reel, monaural, 15-ips magnetic tape masters for the 4-minute 15-second, octophonic tape piece. The 192-page score is, as Cage referred to it, a kind of “dressmaker's pattern--it literally shows where the tape shall be cut, and you lay the tape on the score itself.”

I think you have to have done something really right to get a minute and a half of sustained bravos and boos from an audience of music critics and academics.