 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).
