This is an article written by Will Hodgkinson for "The Guardian" newspaper. I think you can see where I am going with this. Diabolus In Musica. The Devil. Heavy Metal. Music.
Blood On Satan's Claw is a nastily effective, if rather camp, classic British horror film from 1971. The story of a group of 17th-century village "children" (led by the distinctly full-grown Linda Hayden) who turn bad after developing patches of fur on their often naked bodies, Piers Haggard's movie derives much of its power from a score that's at once ominous and beautiful, much like the film's fecund pastoral setting. The secret of the music lies in the use of a troublesome interval, variously banned, feared and celebrated since the 11th century, called the Devil's Interval.
"I used a descending chromatic scale throughout the score," explains Marc Wilkinson, who was director of music at the National Theatre when Haggard approached him to write the score for Blood On Satan's Claw. "To make it scary, I omitted the perfect fifth, which is the one true consonant in the chromatic scale, and highlighted the diminished fifth, which ever since the Middle Ages in Europe has been known as the Devil's Interval."
There shouldn't, theoretically, be anything scary about a musical interval. Just as turning round three times with your eyes closed while reciting the Hail Mary probably won't make the devil appear before you, despite generations of schoolchildren believing otherwise, so playing the note of C followed by F sharp shouldn't encapsulate the essence of evil - but somehow it does. The movement from the first tone in a scale to the fifth, known as the perfect fifth, was the first accepted harmony of the Gregorian chant after the use of the octave. It was discovered in the 11th century that moving down a semitone to the diminished fifth created dissonance, and a nasty feeling of foreboding and dread. The church of medieval Europe quickly banned it, reputedly relying on torturous methods to ensure that the ban was upheld.
"As far as I'm aware there is no symbolic reason for it not being acceptable," says Wilkinson in between demonstrating the Devil's Interval on a piano at his house outside Paris. "It is simply that it feels nasty, an unpleasant sound that yearns to be resolved. Playing it is rather like standing with one foot in the air. You want to move on."
The Devil's Interval does, however, have a foreboding history. The 18th-century violinist Giuseppe Tartini claimed that he composed his Devil's Trill Sonata after Satan himself gave him instructions on how to do it, which might help explain why this piece of music is so incredibly difficult to play. In Wagner's Götterdämmerung, the diminished fifth illustrates a scene of pagan excess; Camille Saint-Saëns used it to tell the story of skeletons coming alive at Halloween in his Danse Macabre. Jimi Hendrix nailed it in the intro to Purple Haze to bring home the message that hallucinogenic drugs may be exciting but they're scary, too.
For some, though, the Devil's Interval has been where they want to stay. "I didn't think I was going to make devil music," says Tony Iommi of Birmingham's metal pioneers Black Sabbath, who used the diminished fifth on the band's 1970 debut to doom-laden effect. "It was just something that sounded right." Ever since, heavy metal bands have used the Devil's Interval whenever evil demands to be summoned - the American band Slayer even named their album Diabolus in Musica after it.
Whether the diminished fifth really does contain diabolical properties or is simply a scary-sounding interval is probably a theological issue rather than a musical one. But in a film about village children slowly changing into a coven of devil-worshiping, human-sacrificing sadists, it appears to have found its spiritual home. Perhaps the most sensible thing to do is to let it stay there, rather than meddle with forces we cannot hope to understand.