That flatted 5th is also called Diabolus en Musica (Latin)
It is a Tritone (tritonus), otherwise known as either an augmented 4th or a diminished 5th.
In medieval times, the Tritone, after being rejected by the Church as the interval of the Holy Trinity due to its extremely dissonant sound, became the interval of the Devil himself, and it was banned and cursed by the Church. They even went so far as to suggest that it invoked the Devil to prevent its use, and a great deal of diabolical superstition became associated with this devilish interval.
After equal temperament came into more common use, the Tritone started rearing its beautiful head of horns and became much less dissonant thanks to the 'everything is slightly out of tune' nature of the new temperament.
It is a Tritone (tritonus), otherwise known as either an augmented 4th or a diminished 5th.
In medieval times, the Tritone, after being rejected by the Church as the interval of the Holy Trinity due to its extremely dissonant sound, became the interval of the Devil himself, and it was banned and cursed by the Church. They even went so far as to suggest that it invoked the Devil to prevent its use, and a great deal of diabolical superstition became associated with this devilish interval.
After equal temperament came into more common use, the Tritone started rearing its beautiful head of horns and became much less dissonant thanks to the 'everything is slightly out of tune' nature of the new temperament.






