Interval
The distance between two pitches, measured in semitones, and the reason some gaps sound sweet and consonant while others sound tense.
Interval
An interval is the distance between two pitches. It is the atom of harmony: once you can hear how far apart two notes are, you can hear everything built from them. Intervals are counted in semitones — the smallest step on the keyboard — and each size has a traditional name: a gap of 7 semitones is a perfect fifth, 4 a major third, 12 an octave.
Why some intervals sound sweet
Consonance is not a matter of taste; it tracks arithmetic. Two tones sound consonant when their frequencies form a simple whole-number ratio, because then their overtones line up instead of clashing. The octave is the simplest ratio of all, 2:1. The perfect fifth is 3:2; the perfect fourth, 4:3; the major third, roughly 5:4. The more complicated the ratio, the more the tones beat against each other and the more tension we hear.
| Interval | Semitones | Approx. ratio | Character |
|---|---|---|---|
| Unison | 0 | 1:1 | identical |
| Major third | 4 | 5:4 | bright, sweet |
| Perfect fourth | 5 | 4:3 | open, stable |
| Tritone | 6 | 45:32 | restless, tense |
| Perfect fifth | 7 | 3:2 | strong, hollow |
| Octave | 12 | 2:1 | same note, higher |
Because Pitch is logarithmic, intervals add: stack a major third (4) on top of a minor third (3) and you get a perfect fifth (7). That simple bit of arithmetic is the seed of every Chord.
Hear the distance
The keyboard fixes a root on C (blue). Move the mouse to pick the second note (orange); the panel names the interval and tells you whether it leans consonant or tense. Click to freeze your choice.