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 an octave apart is therefore 2:1. Further octaves of a note occur at formula_1 times the frequency of that note (where "n" is an integer), such as 2, 4, 8, 16, etc. and the reciprocal of that series. For example, 55 Hz and 440 Hz are one and two octaves away from 110 Hz because they are (or formula_2) and 4 (or formula_3) times the frequency, respectively. The number of octaves between two frequencies is given by the formula: The octave is defined by ANSI as the unit of frequency level when the base of the logarithm is two. After