Music 101: What Is an Octave?

An octave is a musical interval. An octave is defined both in terms of music and in terms of physics:

• In terms of music, an octave is the distance between one note (like C#) and the next note bearing its same name (the next C# that’s either higher or lower).
• In terms of physics, an octave is the distance between one note and another note that’s double its frequency. For instance, the note A4 is the sound of a vibration at 440 Hz. The note A5 is the sound of a vibration at 880 Hz. Going in the other direction, the note A3 is the sound of a vibration at 220Hz.

In the diagram above, which depicts a C major scale, the music goes up from middle C, or C4 (the pitch C in the 4th octave on a piano) to the note C5, which is exactly one octave above it. The C4 vibrates at 261.63 Hz, and the C5 vibrates at 523.25 Hz—its sound waves are double the frequency of C4.

In Western music, octaves are connected in 12 equal intervals. Each of these 12 intervals brings us to a new note. They are as follows:

C
C# / Db
D
D# / Eb
E
F
F# / Gb
G
G# / Ab
A
A# / Bb
B

The notes with slashes can be called by either name, depending upon which key we’re in. For instance, the note F# is found in the key of D and it’s the third interval in the D major scale. But in the key of Eb minor and the Eb minor scale, that same exact pitch is called Gb, due to rules of music theory.

Here’s how the notes allow us to go stepwise, up or down an octave.

• If we go up/down by one interval at a time, such as from the note G to the note Ab, it is said we are advancing in half steps (also called semitones)
• If we go/down by up two intervals at a time, such as from the note G to the note A, we are said to advance in whole steps (also called whole tones)

You can build a path from one note to an octave above it (such as from E5 to E6) that includes every one of the 12 notes. Such a path is called a chromatic scale.

• The chromatic scale moves up exclusively in half steps.
• If you were playing it on a piano keyboard, you’d play every key sequentially, both the white keys and the black keys.
• A chromatic scale doesn’t sound particularly grounded in any one key, and so musicians use it sparingly.
• Nonetheless, chromatic scales can be heard in everything from the classical compositions of Béla Bartók to the jazz-rock guitar solos of Steely Dan.

Most musical scales don’t use all 12 available pitches, however. The building block of Western music is the major scale, which consists of only seven notes. Starting from the lowest note, and going up, they are:

1—the “root” of the scale
2—a whole step up from the root
3—a whole step up from the 2nd
4—a half step up from the 3rd
5—a whole step up from the 4th
6—a whole step up from the 5th
7—a whole step up from the 6th

Unlike a chromatic scale, which moves exclusively in half steps, the major scale mixes whole steps and half steps to create its instantly identifiable sound.

• You can choose any starting note, apply these intervals, and you will produce a major scale.
• For instance, if you start on the note C, and move up in these prescribed intervals, you will get: C-D-E-F-G-A-B before getting back to C.

The second most fundamental building block of Western music is the minor scale. There are three minor scales—natural minor, harmonic minor, and melodic minor—but it’s the natural minor scale (or diatonic scale) that will sound most familiar to Western ears. It is similar to a major scale, but with a few half steps where there were previously whole steps.

1—the “root” of the scale
2—a whole step up from the root
b3—a half step up from the 2nd
4—a whole step up from the 3rd
5—a whole step up from the 4th
b6—a half step up from the 5th
b7—a whole step up from the 6th

So if we were to once again create a scale starting on C, and applied these minor intervals, we would end up with C-D-Eb-F-G-Ab-Bb before getting back to C. And indeed, this is the C natural minor scale, and it connect the note C to the next C above it while producing a minor tonality.

The sound of octaves is very powerful. Two notes played an octave apart make a piece of music sound richer and fuller. Here are few ways musicians have played with octaves over the years:

• The twentieth century Hungarian composer György Ligeti used octaves throughout his 11-part piano suite Musica ricercata, which was famously heard in the film Eyes Wide Shut. Ligeti limited himself to a fixed number of pitches in each movement, so the early movements relied heavily on octaves for melodic variety.
• The jazz guitarist Wes Montgomery famously soloed in octaves rather than single notes, and players have been copying him ever since.
• Bass lines from the disco era were famous for bouncing between octaves in a steady 8th note pattern.
• Horn section arrangers in jazz and pop frequently assign melodies to trumpets, while doubling the same notes two to three octaves lower on a baritone saxophone.
• The legendary DigiTech Whammy guitar pedal allows players to sweep up an octave almost instantaneously. Many rock guitarists have Whammy pedals on their boards, including Tom Morello, whose octave-leaping solo on the Rage Against the Machine hit “Killing in the Name” is a showcase for the pedal.