 In 1968 , Stockhausen composed the vocal sextet Stimmung , for the Collegium Vocale Köln , an hour @-@ long work based entirely on the overtones of a low B @-@ flat ( Toop 2005 , 39 ) . In the following year , he created Fresco for four orchestral groups , a Wandelmusik ( " foyer music " ) composition ( Maconie 2005 , 321 ) . This was intended to be played for about five hours in the foyers and grounds of the Beethovenhalle auditorium complex in Bonn , before , after , and during a group of ( in part simultaneous ) concerts of his music in the auditoriums of the facility ( Maconie 2005 , 321 – 23 ) . The overall project was given the title Musik für die Beethovenhalle ( Maconie 2005 , 296 ) . This had precedents in two collective @-@ composition seminar projects that Stockhausen gave at Darmstadt in 1967 and 1968 : Ensemble and Musik für ein Haus ( Gehlhaar 1968 ; Ritzel 1970 ; Iddon 2004 ; Maconie 2005 , 321 ) , and would have successors in the " park music " composition for five spatially separated groups , Sternklang ( " Star Sounds " ) of 1971 , the orchestral work Trans , composed in the same year and the thirteen simultaneous " musical scenes for soloists and duets " titled Alphabet für Liège ( 1972 ) ( Maconie 2005 , 334 – 36 , 338 , 341 – 43 ) . 
