The interval between the fifteenth harmonic (15X) and eighth (8X) gives the major seventh interval.


This seventh interval is essential when we examine chords formed with four notes.

There are eleven semitones spanning the notes of a major seventh interval.

These chords are known as seventh chords.

The frequency ratio of the major second is 15X/8X= 15:8.

The interval covers seven white positions of the C major scale.

This seventh interval is essential when we examine chords formed with four notes.

There are eleven semitones spanning the notes of a major seventh interval.