Intervals
An interval is the distance between two notes, measured in semitones. Intervals are the most important concept in music theory — they determine whether a chord sounds happy or sad, and whether a melody feels tense or resolved.
The 12 Intervals
Since there are 12 notes in the chromatic scale, there are 12 possible intervals — from 0 semitones (the same note, called unison) to 11 semitones (a major 7th, just one semitone below the octave).
Each interval has a name that describes its quality: Root (0), Minor 2nd (1), Major 2nd (2), Minor 3rd (3), Major 3rd (4), Perfect 4th (5), Tritone (6), Perfect 5th (7), Minor 6th (8), Major 6th (9), Minor 7th (10), Major 7th (11).
Interval Qualities
Perfect intervals (4th, 5th) sound stable and open. Major intervals sound bright. Minor intervals sound darker. The tritone (6 semitones) is the most dissonant interval, historically called the "devil's interval."
In ChordColor
Every note on every instrument is colored by its interval from the current root. A major 3rd is always yellow, a perfect 5th is always blue — regardless of which instrument you are looking at. This is the core of ChordColor's "See the music" system.