Octave (music): hear it in Somewhere Over the Rainbow
An octave is 12 semitones: the same note, higher. Play it, hear it in Somewhere Over the Rainbow, and learn why the frequency doubles.
An octave is 12 semitones: the distance from one note to the next note with the same name, such as C4 up to C5. The upper note vibrates exactly twice as fast (A4 = 440 Hz, A5 = 880 Hz), so the two sound like the same note, higher. Somewhere Over the Rainbow opens with a rising octave.
Listen to a octave
C to C: 12 semitones.
What does a octave sound like?
Empty and pure: the two notes merge so completely that people often think one note was played. Men and women singing "in unison" are usually an octave apart.
Songs that start with a octave
| Song | Direction | Where |
|---|---|---|
| Over the Rainbow (The Wizard of Oz) | Up | the first two notes |
| Take Me Out to the Ball Game | Up | the first two notes |
Titles only. Each melody's opening was checked note by note; songs we were not sure of are left out.
How do you recognise a octave by ear?
- If the second note feels like the same note, only higher or lower, it is an octave.
- A major seventh sounds like an octave that missed; a minor ninth like an octave that overshot.
- On a piano, an octave spans 8 white keys counting both ends (C D E F G A B C): hence "oct", eight.
Quick test: octave or not?
Four sounds. Each one is a octave or one of the intervals people confuse it with. Listen, then pick.
Score: / 4 (your score updates as you answer)
The octave on every note
Intervals are spelled by letter: a octave always spans 8 letter names (the same letter), which is why the top note is sometimes a sharp or a flat.
| From | Octave up | Hear it |
|---|---|---|
| C | C | |
| D♭ | D♭ | |
| D | D | |
| E♭ | E♭ | |
| E | E | |
| F | F | |
| F♯ | F♯ | |
| G | G | |
| A♭ | A♭ | |
| A | A | |
| B♭ | B♭ | |
| B | B |
Octave in numbers
| Measure | Value |
|---|---|
| Semitones | 12 |
| Size on a piano (equal temperament) | 1200 cents |
| Pure (just) ratio | 2:1 = 1200.0 cents |
| Piano vs pure | +0.0 cents |
| Inversion | Unison |
Frequently asked questions
How many semitones are in an octave?
Twelve: every key on a piano, black and white, from one C to the next C.
Why is it called an octave?
Because it spans eight notes of the scale counting both ends: C, D, E, F, G, A, B, C. "Octo" is Latin for eight.
What is the frequency ratio of an octave?
2:1. The upper note vibrates exactly twice as fast: A4 is 440 Hz, A5 is 880 Hz, A3 is 220 Hz. This holds on every tuning system.
What song starts with an octave?
Over the Rainbow from The Wizard of Oz and Take Me Out to the Ball Game both start with a rising octave.