Mahler, who had mobilized the youth of his day against slovenly Tradition, reerupted into a newly youthful popular culture in the 1960s thanks to both the centenary of his birth and the advent of the long-playing record. Not only musicians were touched by the wave of new recordings; modern pop culture and youthful “avant-garde” now blithely bridged the once-opposed realms of “high” and “low”...