[3] With Heinrich Besseler, Stephan went to the University of Göttingen, where he obtained his doctorate in 1950 with a work on Die Tenores der Motetten ältesten Stils by musicologist Rudolf Gerber (1950).
He was a visiting professor in Vienna in 1981, and his colleagues at the Berlin Institute were musicologists Tibor Kneif and Klaus Kropfinger, and from 1984 onwards Jürgen Maehder, who became his Director General from 1990 to 1992.
He has made innovative contributions to the revision of the image of the works of Gustav Mahler, Hans Pfitzner, Max Reger and Paul Hindemith, as well as to the recognition of the importance of the Second Vienna School for the history of music, Arnold Schönberg, Alban Berg and Anton Webern.
[2] As a publisher, Stephan contributed to the general editions of Arnold Schönberg's and Alban Berg's musical works[5] (1989–1996).
[2] Among Stephan's students were the musicologist Reinhold Brinkmann (1934-2010), as well as musicologists Rüdiger Albrecht, Regina Busch, Károly Csipák, Klaus Ebbeke, Thomas Ertelt, Werner Grünzweig, Heribert Henrich, Reinhard Kapp, Ulrich Kramer, Claudia Maurer Zenck, Adolf Nowak, Wolfgang Rathert, Christian Martin Schmidt, Matthias Schmidt, Martina Sichardt, Lotte Thaler and the teacher Bernd Riede.