Led Zeppelin's fourth studio album appeared in 1971 and was officially untitled, though it is known as Led Zeppelin IV. The cover featured four symbols, each chosen by one of the band members. The album included songs such as Stairway to Heaven, Black Dog, Rock and Roll, Going to California and When the Levee Breaks. Singer Sandy Denny provided guest vocals on The Battle of Evermore. Recording took place largely at Headley Grange, where among other things the distinctive drum sound of When the Levee Breaks was created. Musically, the album combined hard rock with blues and British folk. Led Zeppelin IV has sold tens of millions of copies worldwide.