Thrash metal was influenced both by heavy metal and by hardcore punk, the latter of which often incorporated shouted or screamed vocals. The first instance of screaming used as a constant delivery of lyrics was Chuck Schuldiner of the band Death. Musicologist Robert Walser notes, "The punk influence shows up in the music's fast tempos and frenetic aggressiveness and in critical or sarcastic lyrics delivered in a menacing growl." It should however be noted that the vocal delivery of thrash metal is incredibly diverse; some bands such as Anthrax use much cleaner vocals, early Metallica uses very hardcore punk influenced vocals while other bands such as Slayer use more "evil" shouts and yells, bearing little resemblance to hardcore punk. More recent bands within metal's various subgenres, such as Carnifex, are known for making use of multiple variations of both screaming and growling.