Greg Fidelman (born September 4, 1965) is an American music engineer, producer and mix engineer. He has worked with many renowned and highly regarded bands in various genres, many in the heavier rock or metal genres, including Metallica, Slayer, Black Sabbath, Red Hot Chili Peppers, Bush, Audioslave, Marilyn Manson, Slipknot, and System of a Down, but has also worked on albums by U2, Johnny Cash, Neil Diamond and others.