 Karlheinz Stockhausen ( German pronunciation : [ kaʁlˈhaɪnts ˈʃtɔkhaʊzn ̩ ] ; 22 August 1928 – 5 December 2007 ) was a German composer , widely acknowledged by critics as one of the most important ( Barrett 1988 , 45 ; Harvey 1975b , 705 ; Hopkins 1972 , 33 ; Klein 1968 , 117 ) but also controversial ( Power 1990 , 30 ) composers of the 20th and early 21st centuries . Another critic calls him " one of the great visionaries of 20th @-@ century music " ( Hewett 2007 ) . He is known for his groundbreaking work in electronic music , aleatory ( controlled chance ) in serial composition , and musical spatialization . 
