S. T. Erlewine. "Led Zeppelin". Allmusic. Läst 27 september 2010.
google.co.uk
books.google.co.uk
Michael Campbell & James Brody (2007). Rock and Roll: An Introduction. s. 201
Simon Frith, Will Straw, John Street. The Cambridge Companion to Pop and Rock. Cambridge University Press. s. 19
Miller, Jim (1980). The Rolling Stone Illustrated History of Rock & Roll. New York: Rolling Stone. ISBN 0394513223. Läst 5 juli 2012. "Black country bluesmen made raw, heavily amplified boogie records of their own, especially in Memphis, where guitarists like Joe Hill Louis, Willie Johnson (with the early Howlin' Wolf band) and Pat Hare (with Little Junior Parker) played driving rhythms and scorching, distorted solos that might be counted the distant ancestors of heavy metal."
Jane Beethoven, Carman Moore. Rock-It. Alfred Music. s. 37
web.archive.org
S. T. Erlewine. "Queen". Allmusic. Arkiverad från originalet den 12 februari 2011.