By 1971’s IV, Led Zeppelin had mastered thumping blues, gentle acoustical folk, hard rock, and even pop. Producer/guitarist Jimmy Page had a real ear for sonic textures (like the soaring orchestral crescendo here on “When the Levee Breaks") that changed forever how hard rock would be heard and recorded. Loose-limbed anthems like “Rock ’n’ Roll” dovetail with lilting epics like “Stairway to Heaven," revealing a band at the height of their musical and rock-mystical powers.