The tritone or 'Devil's Chord' – a musical interval, such as the augmented fourth, spanning three whole tones – has a long musical history of links to diabolism, from the Church's wholesale banning of it in the Middle Ages, through the Romantic era, blues and jazz, to modern film music and death metal.

Before the proscription of the interval it was, according to Professor John Deathridge, King Edward Professor of Music at King’s College London, often used to represent the presence of evil: "In mediæval theology, you have to have some way of presenting the devil. Or if someone in the Roman Catholic Church wanted to portray the crucifixion, it is sometimes used there." Later, though, it came to be seen as a dissonance, and was outlawed, says Deathridge, on technical grounds in which, perhaps, a theological ban can also be read.

Romantic portrayals of evil – particularly in the works of Wagner – brought the tritone's tension-inducing power to the musical fore, and modern musicians – from film composer Bernard Hermann to seminal 'metal' act Black Sabbath – have drawn on these associations to add a spooky atmosphere to their own work.