Estimated reading time 2 minutes
Table of Contents
Introduction
Are you confused about what an octave is? Or are you a music teacher with a student that doesn’t understand how they work? Octaves are one of the most fundamental music theory concepts. When teaching music students, it helps to demonstrate them on a keyboard instrument, so I’ve created a keyboard diagram you can reference. Keep reading How to Explain an Octave to an Absolute Beginner Musician? to dive into the theory.
This article uses musical terms. For definitions, see the Glossary at the end of the post.
How to Explain an Octave #1: Finding Patterns on the Keyboard
Mobile users: for best results reading the music, rotate your screen 90o to the right.
The interval from C3 to C4 on the keyboard diagram above is an octave:
- So, what does the word interval mean?
- An interval is a distance.
- Specifically, it measures the number of keys on a keyboard instrument.
Look at the keyboard diagram:
- Start on any white-key note. Then, count eight white-key notes (including the note you started on) to the right or left.
- The key you land on will have the same letter name as the key you started on. (That is, if you didn’t end up going right off the diagram.)
- This is why it’s called an “octave,” because the prefix oct- means “eight.”
I ask my young students, “How many arms does an octopus have?”
- Answer: Eight.
- Then, I ask, “How many notes does an octave have?”
- Answer: Also, eight.
Every time you go eight letter name notes on the keyboard, you repeat the same note.
How to Explain an Octave #2: Eight Notes but Twelve Keys
Even though there are only eight letter name notes, there are twelves keys on a keyboard instrument between C3 and C4:
- Why? Because the keyboard originally had only white keys (plus one black key: Bb).
- The other black keys were added later.
- This explains why it’s easier to start visualizing octaves using the white keys.
How to Explain an Octave #3: Why Do We Hear the Two Notes as Being the Same? (Warning: Advanced Theory!)
The keyboard also shows other relationships:
- Notice that between C3 and C4 on the keyboard diagram there is a group of two and a group of three black keys. This pattern repeats with each successively higher or lower C.
- In other words, musical patterns will repeat with every octave. Therefore, you can play melodies in higher and lower octaves, and they’ll be recognizably the same.
- Try it for yourself. (For a virtual piano: click here.) Next, as you play the virtual piano, listen to how C3 and C4 sound as they overlap. The octave has a sense of identity that the other intervals lack.
The technical explanation is that C3 and C4 have a 2/1 frequency ratio:
- Because this is true, the harmonic overtones of these two notes will be virtually the same.
- The chart below shows the harmonic overtones for the notes of a C major triad.
- Notice that the root note and the octave note have the same overtones (the octave note has all the same harmonics as the lower root note, even though this chart doesn’t show it). However, the octave’s overtones are higher.
- By contrast, the third and the fifth of the chord mostly have different overtones from the root note.
- Therefore, the implication of the 2/1 frequency ratio between C3 and C4 means that our ears hear the two notes as being the same. However, C4 will be perceptibly higher.
Final Thoughts
The takeaway points:
- Every time you go eight letter name notes on the keyboard, you repeat the same note.
- This is why it’s called an “octave,” because the prefix oct- means “eight.”
- Octaves have a sense of identity that the other intervals lack.
Related Posts
- Singing Intervals
- What Purpose Do Accidentals Serve in Reading Sheet Music?
- D’you Want Some Music Tips and Tricks I’ve Learned Over the Years?
© 2024 Geoffrey Keith
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