Thrash was essentially the sound of underground heavy metal during the '80s, dominated by a driving, percussive approach to rhythm guitar (thanks to a pick-hand technique called palm muting) and furious levels of aggression. Thrash was often technically accomplished, taken at fast tempos, and emphasized heavy, sometimes atonal guitar riffs over melody; however, these generalizations are far from absolute rules. In its early days, thrash was essentially the same thing as speed metal, the product of American bands who in the early '80s fused the lean, vicious attack of the New Wave of British Heavy Metal with the tempos of hardcore punk and Motorhead.