Music Theory Intervals
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Interval: The distance between two notes
Semitone: The smallest interval we have in western music. Moving up a string by one fret on a guitar or going to the very next note on a piano are both examples of a semitone.
Semitone = Half Step
2 Semitones = 2 Half Steps = 1 Whole Tone = 1 Whole Step
The 2 Parts of an Interval
There are 5 different qualities of intervals:
Perfect intervals are so-called as they have nearly-perfect consonance. In other words, they sound REALLY pleasant and agreeable.There are only 4 perfect intervals: Perfect Unison (or Perfect 1st - aka the same note as the original), Perfect 4th, Perfect 5th, and Perfect Octave (perfect 8th).
This leaves the 2nd, 3rd, 6th, and 7th that do not have a perfect interval. These numbers have major and minor intervals instead.
1st, 4th, 5th and 8th all have perfect intervals, so the 2nd, 3rd, 6th, and 7th are left to split between major and minor.
The major interval is always 1 semitone higher than the minor. The major is also the “happier” sounding of the major and minor intervals.
Any interval that can be major can be minor. Take away one semitone from a major interval, and you have that minor interval.
Minor intervals tend to sound darker and more sad than major intervals.
Augmented intervals are one semitone higher than a Perfect or Major interval.
Perfect + 1 semitone = Augmented
Major + 1 semitone = Augmented
Diminished intervals are one semitone lower than a Perfect or Minor interval.
Perfect - 1 semitone = Diminished
Minor - 1 semitone = Diminished
So, if we put all this information together, you’ll notice that intervals always follow a pattern. With “->” representing going up 1 semitone, this is what we have:
Diminished -> Minor -> Major -> Augmented
Diminished -> Perfect -> Augmented
The quality of interval is combined with the number of the interval. Usually, the number is simply the distance between letter notes.
Do you understand the alphabet? Good, because that’s all you need here. For example, how far away is G from C? C, (D, E, F), G. Since we count both the start and end note, this would be a 5th.
B from C? C, (D, E, F, G, A), B => 7th
E from C? C, (D), E => 3rd
3 Rules of Intervals
Next I’m going to give you 3 rules to remember that will help you think through intervals.
Incrementing up by one quality will always be going up 1 semitone
Minor 2nd -> Major 2nd = Up 1 semitone
Diminished 7th -> Minor 7th = Up 1 semitone
Augmented 6th -> Major 6th = Down 1 Semitone
Incrementing up by one number will always be going up 2 semitones
Minor 2nd -> Minor 3rd = Up 2 semitones
Perfect 4th -> Perfect 5th = Up 2 semitones
Major 6th -> Major 7th = Up 2 semitones
Major 3rd -> Major 2nd = Down 2 semitones
All numbers have either perfect or both minor and major intervals, not both
There is a Perfect 4th, there is not a minor or major 4th.
There is a major and minor 3rd, there is not a perfect 3rd.