Simply a harder, louder form of rock than what was generally explored in the hippie heydays of the late sixties, Black Sabbath all but created the sound we know as metal today by down tuning their guitars, turning them up, and playing slowly and seriously. With an emphasis on guitar and often shrieked/growled/shouted vocals (but not always), metal is typically seen as rock music's more extreme, less forgiving cousin. The genre has since expanded into every conceivable direction, from fusions with jazz to classical to hip-hop.