 Other major pioneers of the heavy metal genre had begun as blues-based psychedelic bands, including Black Sabbath, Deep Purple, Judas Priest and UFO.According to American academic Christophe Den Tandt, many musicians during the post-psychedelic era adopted a stricter sense of professionalism and elements of classical music, as evinced by the concept albums of Pink Floyd and the virtuosic instrumentation of Emerson, Lake and Palmer.