Heavy metal has long been the bane of rabid Christian groups who fear that metal music leads kids into satanism and suicide. How could they not? The genre has been built on the idea of the devil since Black Sabbath decided to play “horror music” as a change from jazz.
It turns out that a lot of metal music has made use of what’s known as the Devil’s Interval or the Devil’s Tritone. This is a combination of two notes that give a “spooky” effect. If you want to know what it sounds like, think of the first bit of the Simpsons theme tune (the “Simp” part of “The Simp..sons”). According to the BBC:
On the surface there might appear to be no link between Black Sabbath, Wagner’s Gotterdammerung, West Side Story and the theme tune to the Simpsons.
But all of them rely heavily on tritones, a musical interval that spans three whole tones, like the diminished fifth or augmented fourth. This interval, the gap between two notes played in succession or simultaneously, was branded Diabolus in Musica or the Devil’s Interval by medieval musicians.
A rich mythology has grown up around it. Many believe that the Church wanted to eradicate the sounds from its music because it invoked sexual feelings, or that it was genuinely the work of the Devil.
The tritone is used extensively in Black Sabbath’s eponymous song:
Guitarist Tommy Iommi says: “When I started writing Sabbath stuff it was just something that sounded right. I didn’t think I was going to make it Devil music.”
Other examples of the Devil’s Interval include Purple Haze and Foxy Lady by Jimi Hendrix and Maria from West Side Story.