#augmented 4th

In those days composing music was very much an act of praising God. The music should therefore be beautiful and moving. The Augmented 4th, or Tritonus, which spans three whole steps in the scale, is one of the most dissonant musical intervals around. It was considered unpleasant and ugly, and was named 'diabolus in musica' - 'the devil in music' - and you wouldn't use anything diabolical to praise the Lord, would you?

There are strict musical rules. You aren't allowed to use this particular dissonance. It simply won't work technically, you are taught not to write that interval. But you can read into that a theological ban in the guise of a technical ban.

"It can sound very spooky. It depends on how you orchestrate. It is also quite exciting. Gotterdammerung has one of the most exciting scenes - a pagan, evil scene, the drums and the timpani. It is absolutely terrifying, it is like a black mass... There is a big connection between heavy rock music and Wagner. They have cribbed quite a lot from 19th Century music.

It was recognised to be a problem in music right back to the 9th Century. It is a natural consequence, and so they banned it. They had rules for getting around it. It was called Diabolus in Musica by two or three writers in the medieval or renaissance [period]. It was 'false music', the intervals weren't natural.

[Dissonance] is something that yearns to be resolved. A very good example would be the opening of West Side Story, Maria. It wants to resolve into the next note. It is a special kind of tension. It gives that angular, edgy, spooky feel. Film music is often extremely sophisticated at signalling to a listener here is a particular kind of character. It is a leitmotif, first used by Wagner.

The augmented 4th (the interval between the two tones of a fire-engine klaxon) exerts its unsettling effect even when the notes are sounded in succession and in conventional harmony and counterpoint, its use is still subject to rules and regulations. While the interval, used judiciously, gives vigour and interest to what would otherwise be rather anodyne melody, the churchmen thought its disturbing effect 'apt to provoke lewd and libidinous thoughts'. Naturally the ban ensured that the augmented fourth became a favourite device of church composers, and much later it was re-invented, labelled 'flattened fifth' and somewhat overused by young jazz players anxious to dissociate themselves from traditional styles.

The augmented fourth interval became the hallmark, in the '40s and '50s of the type of jazz known as Bebop, whose exponents called it 'the flattened fifth'. Jazzmen of that era also had a hand sign which consisted of a high five but with the thumb folded in to the palm. This gesture, used as a greeting between jazzers, was known as 'the sign of the flattened fifth' and was often accompanied by expressions such as Oolya Koo, man! Perhaps this explains why jazz has been called 'the devil's music'.

This interval was banned from church music because of its sound but is heavily used in death metal music. It is very hard to sing unless the vocalist employs a false chord technique, also known as a scream or a growl which is often used in death metal music. Death metal music is not something that is directly related to the devil. In our world, there exists two basic moods and sounds, one of beauty and one of which is ugly. The augmented 4th is the perfect choice of interval to express the later mood.