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.