The musical staff pictured here looks perfectly innocent, does it not? Yet at one time, these combined notes were banned by the Catholic Church from musical composition, and were claimed to have the ability to summon Satan himself.

Such is the power of music to affect human emotions, that the tritone has become known since Medieval days as 'the Devil's interval.' The tritone interval spans three whole tones on the musical scale. As such, the Church originally assumed that three tones must correspond with the the Holy Trinity, making the tritone the interval of God. This concept was rejected however, as the dissonant, disturbing effect of the tritone was undeniable, and it became associated with the Devil instead

In the Romantic period of classical music, the emotional effect of the tritone was used in transitioning from one key to another. The tritone has long been used in music for the movies, particularly in science fiction, horror and film noir.

In the modern era of heavy metal music, the Devil's interval became an often invoked sound, to conjure emotions of dread and evil.