Octave
The octave spans 12 semitones and 8 steps (C–C′). Inversion: unison. To remember it: »Somewhere Over the Rainbow«, the first two notes.
- Semitones
- 12
- Steps
- 8
- Quality
- perfect
- Inversion
- unison
- Sound
- perfect consonance
In notation
First one after the other, then together — the distance as a step and as a sound.
On the keyboard
On the guitar: 12 frets higher on the same string.
How to count it
Counting 8 steps up from C — C, D, E, F, G, A, B, C′ — lands on C′. The number of steps gives the name: a octave. In between lie 12 semitones — the perfect size; one semitone less would be diminished, one more augmented.
Move the lower note up an octave and what remains is the unison: semitones add up to twelve, steps to nine.
Perfect consonance — the sound is at rest.
To remember it
»Somewhere Over the Rainbow«, the first two notes.
Where it occurs
In every chord as soon as a note is doubled — on the piano usually the octave in the bass.
Related
In the glossary: octave · Ear training: hear intervals and guess them · All intervals
Anotona does this for you
Photograph a page of sheet music or play the melody — Anotona finds the key, engraves the notes and transposes them into any other. Free.
See AnotonaEvery note on this page is computed, not typed in — following the rule that also makes F# major spell its seventh degree E#, not F.