Hi everyone! Thanks for stopping by! So what's all this about the devil, and why would he have his own interval? Did the Catholic Church in the Middle Ages really excommunicate musicians and composers who used it? And what the heck is so evil about it anyway?
The technical names for this interval are the tritone, augmented fourth, or diminished fifth. To listeners accustomed to western music, it's the most dissonant interval in existence. It's almost painful. If you were to end a piece of music with this thing you'd risk being chased out of town with pitchforks. (But not excommunicated - that's an urban legend.)
The tritone, if you really insist on knowing, is created by starting with any note, then pairing it with another note that's three ("tri-") whole steps ("tone") away. So if you start with let's say F, the note that's three whole steps away is B.
How did I figure that? The first whole step is from F to G, the second is from G to A, and the third from A to B. It also works in reverse. (It helps if you can picture a piano keyboard in your head.) So our tritone would be F with B either below or above it.
If you're near a keyboard, give it a try. I dare you.
Ok, so what are you supposed to do with this diabolical sound? Well, it actually comes in pretty handy.
Using the easy-peasy C major scale as an example, the tritone interval occurs naturally in the G7, or dominant seventh, chord G-B-D-F. The dominant seventh is an extremely common chord that's used in just about every genre of music ever created. Ever.
When you play it and then follow it with the tonic triad, in this case C-E-G, it sounds very familiar and perfectly wonderful. That's because the tritone lurking inside the dominant seventh chord acts like a V8 engine driving that chord to the tonic. Those two notes, B and F, are each a half step away from C and E respectively, which you could say are two of the most important notes in the C major scale.
Geeky music types call this "resolution" - the opposite of tension, which is what the tritone has gobs of.
What's interesting about this IMHO is that even a listener who knows nothing about music theory whatsoever will start feeling very squirmy if you keep banging out a tritone in your music without resolving it. Listeners will only let you mess with their ears to a certain point before, well, they start going for the pitchforks. So handle your tritones with care, people!
I hope you found this helpful! Feel free to get on your soapbox or show me who's boss and leave a comment. Or you could just say hello. That would be even nicer.
See you next time!