Musically, doom metal is strongly influenced by the early work of Black Sabbath. A number of their early songs, such as "Black Sabbath" and "Into the Void" are considered embryonic or prototypical doom metal songs. Their third album, Master of Reality (released in 1971), features Tony Iommi's guitar and Geezer Butler's bass tuned down to C# for heavier riffing and reduced string tension for Iommi's previously injured fingers.