The Architecture of Music

The Circle of Fifths

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Perfect Fifth Intervals

Whether notes are played sequentially as in a melody, or simultaneously as in a chord, there are two ways to describe the way a combination of notes will sound: intervals and P5 intervals. Intervals are the distance in semitones between notes (eg. C to E is a maj3 or 4 semitones). However, this is not always a good way to describe how two notes will sound together because certain intervals between notes—such as the min2—sound highly dissonant when played simultaneously. The min2 (equal to one semitone) is arguably one of the most dissonant sounds a combination of two notes can make, or the sound heard when two notes are slightly out of tune.

Instead, we can use perfect 5th intervals equal to seven semitones to describe the sound of two or more notes. They describe the sound created between notes better than semitone intervals because two notes played one P5th interval apart sound in repose. Study the diagram on the following page to understand the difference between intervals and P5th intervals. The harmonics give us a way to analyze sound using a phenomenon of nature that describes the way two or more notes sound together. By placing all the P5th intervals next to each other, we can now see the relationships of all the notes based on the harmonics.

Perfect Fifth Intervals