Octave

12 semitones — the same note, one register higher

Degree 8Solfège: doNotation: P8

The octave is an interval of 12 semitones. Two notes an octave apart share the same name, degree, and (in NoSheet) color; they sound like the same note at different heights, which is why only 12 unique pitch classes exist. It is perfectly consonant — the most consonant interval of all, the higher frequency exactly double the lower (2:1 ratio, the 2nd harmonic). Unlike the perfect 5th, it creates no movement — it reinforces rather than progresses. Each degree appears once within an octave, defining the bounds of NoSheet's single-octave challenges; full-range challenges span several.

35791215171921CCCCCCCCCCC
The instrumentTap a note to hear it.
The octave in the harmonic series
ff completes 1 cycle in one period of the sum1 cycle2f2f completes 2 cycles in one period of the sum2 cycles3f4f5f6f7f8f9f10f11f12f13f14f15f16fsum2:1 — the higher note vibrates 2 times for every 1 of the lower: harmonics 2 and 1 of one fundamental2:18: the octave — the interval's degree above the root, as the app writes it8The sum repeats every 1 cycle of f — the shorter this is, the more simply the two notes fit together, and the more consonant the intervalrepeats every 1 cycle16 cycles of f
Harmonic seriesEach row is one harmonic of the note — n times the fundamental's frequency, about 1/n of its strength — faster and fainter as it climbs. The rows in ink are where the chosen interval first arises. The bottom row is the one your ear actually receives: those rows added, a single wave. The shaded band is one repeat of it — the shorter that pattern, the sooner the ear settles on it as one sound. Harmonics 1 and 2 — the ratio 2:1: a octave. Together they repeat every 1 cycle of the lower note — the shorter that pattern, the sooner your ear has heard it come round enough times to settle on one sound.

Related

Contained byIntervalsRelatedSolfègeSingle OctaveFull RangePerfect 5thConsonanceDerived fromHarmonic SeriesReferenced byPitchPitch ClassSemitoneChromatic Scale

Practiced in

Octave Bounce