Studied in Detmold and Hamburg with György Ligeti before accepting a position in 1980 as Professor at the Conservatory of Music and Dance in Cologne, Germany. His early works are composed in a constructivist manner, as in his orchestral work TURMALIN (1984). In the 90's he turned his attention to an intensive study of the compositional process, leading to the development of a more subtle and „pure musical language. A series of ensemble and chamber works from this period can be heard in two Portrait CD recordings (Talking Music, 1998 and Cybele, 2001). Further investigations address the influence of expressive and semantic elements within a musical context - examples of which can be heard in LÄNDLER (2001) for ensemble and WASSER, ROSEN (2007) for seven instruments. In more recent years Jaecker has turned to include the element of room and space in his compositions, as in HARRY'S DREAM (2012), IN UNS (2013) for 25 voices in 5 groups and 2ND FLOOR for 12 pianos, 12 doors and 7 contrabasses (2016).