Seventh chord an augmented fifth, and an augmented seventh (i.e., a sequence of 3 major thirds, such as C–E–G–B), is a rarely used tertian seventh chord. The reason is that the augmented seventh interval is enharmonically equivalent to one entire octave (in equal temperament, 3 major thirds = 12 semitones = 1 octave) and is hence perfectly consonant with the chord root. The seven commonly used chords are: Seventh chords can also be constructed using augmented or diminished thirds. These chords are not tertian and can be used in non-tertian harmony. There are many (mathematically, 64) chords that can be built, however,
Pitch interval Thus the ordered pitch class interval, i<"x", "y">, may be defined as: Ascending intervals are indicated by a positive value, and descending intervals by a negative one. Pitch interval In musical set theory, a pitch interval (PI or ip) is the number of semitones that separates one pitch from another, upward or downward. They are notated as follows: For example C4 to D4 is 3 semitones: While C4 to D5 is 15 semitones: However, under octave equivalence these are the same pitches (D4 & D5, ), thus the #Pitch-interval class may be used. In musical set theory, a pitch-interval class