In music theory an interval refers to the distance between two notes.
Every interval has its own name, for instance the interval between C and G is called a perfect fifth, the interval between C and D is called a major second.
Every interval has not only a different name, but also a different sound.
Some intervals, like the perfect fifth, sound pleasing to the ear, and are considered as consonant intervals. Intervals of a major second sound less stable, and are thus considered dissonant.
One may think this means that to make beautiful music you should only play consonant intervals since they are the most pleasing to hear.
In reality, this is rarely the case and the aim of this lesson is to show you the value of dissonance, and that the magic happens, not when there is a series of consonant intervals, but when consonant and dissonant intervals are blended together to make beautiful melodies.
The study of different intervals, their names, and how they form scales or chords, goes beyond the purpose of this lesson but you should definitely consider learning music theory if you’re not doing so already. Read this article to learn what music theory is not – and what it really is.
In these examples I will be using only 3 intervals
- Perfect fifth – Very consonant
- Perfect fourth – less stable than the perfect fifth, but still, a consonant interval
- Augmented fourth – also called the Tritone, an interval so dissonant that also got itself nicknamed “the Devil’s interval” through the years.
Play these 3 intervals on your guitar (or any other instrument) and listen carefully to their different sounds.
Notice that when you play the augmented 4th, the tritone, your ear wants to hear another note, to resolve the tension that has been created.
In the first example, we are going to resolve the augmented 4th interval into a perfect 4th from the root.
The root note (C) moves up an augmented 4th to an F#. This creates tension but it soon resolves to the note F which is a perfect 4th from the root note C
Though the perfect 4th is less consonant than the Perfect 5, after the dissonance of the tritone, it sounds stable enough to resolve to.
Next, we’re resolving the Augmented 4th (F#) into the Perfect Fifth (G) from the Root (C)
Notice what a different effect it produces.
And if you’re saying “where have I heard this before”, it’s probably because it’s the same sequence of notes that opens the theme for “The Simpsons”
In all the examples above, the augmented 4th resolves on either a perfect 4th or a perfect 5th note from the root.
But what if the augmented 4th not resolved? What if, instead, you end on the triton?
Well, if you’re reading this lesson while preparing for music theory exams, I suggest you wouldn’t even try to end of the triton.
If, on the other hand, you’re a rock and roll rebel, you know that the rules are there to be broken.
Which is exactly what Tony Iommi did when he wrote the song “Black Sabbath”
Many heavy metal fans credit Tony Iommi for being the father of heavy metal, and some even consider the song Black Sabbath as having given birth to the whole genre.
This is the intro riff to “Black Sabbath” (I simplified it a bit, Tony Iommi embellishes this with an ornamental trill, which goes beyond the purpose of this article).
The notes in the first and second bar are both G, with an interval of an octave between the two.
But the third note – the one there is the emphasis on, is the augmented 4th, the triton, the devil’s interval.
And this is the beautiful thing about music. The rules can be creatively broken.
Music theory is like a path, and you want to walk that path because it’s the path great composers have followed – there is no doubt that it works.
But sometimes you want to stroll away from that path, you may want to discover an intriguing cave behind the rocks – like Tony Iommi did when he broke all the rules and ended the phrase of his iconic riff with the most dissonant note of all.
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