Complex sentence: By 1986 he had composed the music for a dance piece, RAB which premiered at the Avignon Festival, and was touring worldwide with The Harmonic Choir, David Hykes' experimental vocal group which specialized in overtone singing.
Split into simpler sentences: By 1986 he had composed the music for a dance piece, RAB which premiered at the Avignon Festival. At the same time, he was touring worldwide with The Harmonic Choir, David Hykes' experimental vocal group which specialized in overtone singing.