Philip Glass's most unusual and challenging work has often been motivated by other artists and different media — think of Allen Ginsberg's poetry for his Symphony No. 6 or the lyrics of David Byrne and Paul Simon on “Songs from Liquid Days.” And so it was with the 1996 “Heroes” Symphony, a symphonic rendition of the classic 1977 David Bowie album of the same name. Each of the symphony's six movements is based on a song from that record, considered a landmark of pop experimentalism in its day. While Glass adds his own trademark overlay of oscillating motifs, the treatments are all remarkably straightforward; if you're looking for a good introduction to Glass's sound world, this could be the album for you.