In Music theory, what is an octave?
Two notes where the higher note is twice the frequency of the lower note.
In music theory, an octave is an interval (distance between two notes), where the higher note is twice the frequency of the lower note. For example, you might have an octave of two C notes, but one sounds much lower than the other. On the guitar, octaves are separate by 12 half steps (12 frets).
In western music, an octave is an interval with two notes at a different pitch. For an interval to be an octave, the higher note has to be two times the pitch of the lower note. The distance between these two notes is 12 steps, which is equal to 12 frets on the guitar.
On the guitar, there are a lot of different ways you can have an octave. For example, the third fret on the fifth string is a C, while the fifth fret on the third string is also a C, though an octave higher than the original.
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An octave on a guitar
Here's a guitar tab that gives you an example of an octave in the key of C:
Here's a simpler way to write it:
- 3rd fret: Lower C note in the octave
- 5th fret: Higher C note in the octave
Another way to form an octave on a fretboard is by going from the open string note, E on the sixth string for example, to the note 12 frets (also called half steps) above it. Here's a tab image showing the jump.
The numbers of octaves
Another way to think about octaves, if you want to get into more detail, is in terms of frequency and pitch. You don't have to know this to play guitar or piano, but it can help you become a better music theory student.
Notes are measured in hertz (Hz), which means the number of wave cycles or oscillations a note makes in a second. Higher Hz per second means higher pitch.
So here's how it would look in an octave:
- Low E note on a guitar's open 6th string: 82.41 Hz
- High E note on the guitar's 6th string, 12th fret: 164.41 Hz
So we see that the wave cycles of the root note are roughly half that of the higher note. That is the formal way to define an octave - the mathematical approach.
Questions or thoughts?
So octaves aren't all that scary. In application, they're actually quite simple. You don't even need to get into the fine details.
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