He was a professor at the University of Oslo from 1965 to 1998, and is probably best known for his long-term research on composer Edvard Grieg.
[2] Among his books is a study of composer Johannes Haarklou from 1961, Waldemar Thrane from 1961, and Musikklære (English: Music theory) from 1963.
[2] He co-wrote the biography Edvard Grieg – mennesket og kunstneren together with Dag Schjelderup-Ebbe in 1980, a work that has been translated to several languages, including English, German and Russian.
[4] From 1980 to 2004 he chaired the committee responsible for publishing the twenty volumes of Grieg's Collected Works.
He held honorary degrees as St. Olaf College from 1993 and Westfälische Wilhelms-Universität from 1996.