For their fourth studio album, Black Sabbath expanded their sound to include the unlikely ballad “Changes,” which featured guitarist Tony Iommi on piano and the Mellotron he had taught himself to play while partying in the Bel Air mansion that the entire band lived in during the making of the album in Los Angeles. Such craziness was standard-issue for the era, and the trippy-indulgent instrumental “FX,” the warped time signatures of “Cornucopia,” and the cocaine-praising “Snowblind” further exposed and reflected the tenor of the times. Though this album took longer than usual to make, it features some of the band's best music. The opening “Wheels of Confusion/The Straightener” includes both the standard heavy Sabbath riffs and a complex instrumental jam over its eight minutes. The churning “Tomorrow’s Dream” didn’t chart as a single, but bands of Sabbath’s unusual heaviness were clearly album artists without pop-chart concerns. Other key tracks like “Supernaut,” “St. Vitus Dance," and “Under the Sun/Every Day Comes and Goes” further cemented their reputation as the band writing the rules of heavy metal as they went along.