Augmented seventh Augmented seventh In classical music from Western culture, an augmented seventh is an interval produced by widening a major seventh by a chromatic semitone. For instance, the interval from C to B is a major seventh, eleven semitones wide, and both the intervals from C to B, and from C to B are augmented sevenths, spanning twelve semitones. Being augmented, it is classified as a dissonant interval. However, it is enharmonically equivalent to the perfect octave. Since an octave can be described as a major seventh augmented by a diatonic semitone, the augmented seventh is the sum of an octave,
Octave mandolin also varies widely, from as few as 17 to as many as 24 frets: 18 or 19 frets is typical. From the mid-20th century on, a number of makers have produced octave mandolins with guitar-shaped (e.g., the "hourglass" or "figure-8") bodies. These instruments are typically constructed essentially like acoustic guitars, with similar woods and internal bracing. the neck, however, is much narrower, and supports the mandolin string layout, rather than the traditional 6-strings of the guitar. As with the mandolin and mandola, the octave mandolin has four courses of two strings each. The two strings in each course are tuned