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 experience octave equivalency, and its biological basis apparently is an octave mapping of neurons in the auditory thalamus of the mammalian brain. Studies have also shown the perception of octave equivalence in rats , human infants , and musicians but not starlings , 4–9 year old children , or nonmusicians . Most musical scales are written so that they begin and end on notes that are an octave apart. For example, the C major scale is typically written (shown below), the initial and final C's being an octave apart. \override Score.TimeSignature #'stencil = ##f \relative c' { </score> Because of