A death growl, or simply growl, is a vocal style (an extended vocal technique) usually employed by death metal singers but also used in other heavy metal styles, such as metalcore. Death growls are sometimes criticized for their "ugliness" and for being difficult to understand without a lyric sheet. However, the harshness of death growls is in keeping with death metal's abrasive music style and often dark and obscene subject matter. The progressively more forceful enunciation of metal vocals has been noted from heavy metal to thrash metal to death metal and some black metal.