Halloween week subject.... also interestingly posted on this Agnostic website: The Devil's interval... mooowaa haha!!

Everyone knows the sounds of Halloween: creaky floorboards, howling winds, the amplified sound of a beating heart. But back in the day, the devil was said to exist in a particular musical tone. For centuries, it was called the devil's interval — or, in Latin, diabolus in musica. In music theory, it's called the "tritone" because it's made of three whole steps.

"The reason it's unsettling is that it's ambiguous, unresolved," says Gerald Moshell, Professor of Music at Trinity College in Hartford, Conn. "It wants to go somewhere. It wants to settle either here, or [there]. You don't know where it'll go, but it can't stop where it is."

There used to be rules against writing music that contained this interval. Moshell says that during the Renaissance, all music had one purpose: to be beautiful and express the majesty of God. Anything otherwise was studiously avoided. But once music was no longer shackled to the church, it was free to express all kinds of tension. The devil's interval was ideal for that.

From classical to jazz to rock and even Broadway musicals, the tritone conveys feelings ranging from forbidden love and longing to fear and defiance. Listen below to a selection of songs that contain this unsettling tritone and hear the radio version at the audio link above.