in music. (1) An interval encompassing the eight steps of the diatonic scale or six whole tones. It is one of the perfect consonances. From the acoustical point of view, an octave is the interval between two frequencies f1 and f2, the logarithm of whose ratio to the base 2, in other words log2 (f2/f1), is equal to 1. This corresponds to the ratio of the upper cutoff frequency to the lower cutoff frequency, which equals 2(f2/f1 = 2). One octave equals 1,200 cents or 301 savarts.
(2) The eighth step of the diatonic scale.
(3) A progression of musical notes that comprises all the basic notes—C (do), D (re), E (mi), F (fa), G (sol), A (la), and B (si) —or the 12 semitones of the chromatic scale. The entire range of notes used in music encompasses seven complete octaves and two incomplete octaves. These octaves progress from the low notes of the musical range to the high notes in the following order: subcontraoctave (an incomplete octave, possessing only three upper notes—A, B flat, and B), contraoctave, great octave, small octave, one-line octave, two-line octave, three-line octave, four-line octave, and an incomplete octave (in Russian, fifth octave) consisting of the single note C.