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The problem it solves
To find a note on your instrument, read it on the staff or say it to someone else, you need a stable system of names and to understand why the same name reappears higher and lower.
Detailed theory
Key idea
There are seven note names; when they run out, they start over from the beginning.
When a name repeats, you've covered one octave: the frequency has doubled going up, or halved going down.
Understand it
The music we use every day is built from only seven note names: C, D, E, F, G, A and B. When you reach B, the next sound is a C again and the series starts over from the beginning.
That new C isn't the same sound as the previous one: it is higher. The distance between a note name and its immediate repetition is called an octave, and it corresponds to doubling the frequency. That is why a C and the C an octave above sound like the same note, but the second vibrates exactly twice as fast.
Since the same name appears many times, we add a number to place it: C3, C4, C5. C4 is the piano’s middle C, the reference we use to order the rest of the notes from low to high.
Think of the days of the week: there are only seven and, when Sunday ends, a Monday starts again, but already of a different week. Notes work the same way —seven names going round in a circle— and the octave number is like saying which week you mean.
How to recognise it
How it's written
On the staff, every line and space is a note; when you go up seven positions in a row you return to the same name, one octave higher. The number (C4, C5) tells you which repetition you're on.
How it feels
Sing a note and look for it higher until it sounds the same but brighter: that is the note one octave above. It feels like finding the same voice again in a clearer tone, not a new note.
Common mistake
Saying only a note's name without the octave: talking about 'a C' isn't enough if you don't know whether it is C3 or C5.
Thinking C4 and C5 are the same sound because they share a name; they share identity, but they live in different registers.
Try it
On the keyboard, play every C from bottom to top: you will hear the same name repeating, each time higher.
Start from middle C (C4) and count seven white keys up to the next C (C5): you have just gone up exactly one octave.
On the instrument
An octave doubles the frequency
The seven names climb C, D, E, F, G, A, B... and when they reach the top a C comes round again, one octave higher. Tap each key to hear it.
Staff & keyboard
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Els set noms pugen C, D, E, F, G, A, B... i en arribar a dalt torna a sortir un C, una octava més amunt. Toca cada tecla per sentir-ho.
Where it's used
- Talking with other musicians
- Saying 'C4' so everyone plays exactly the same pitch.
- Finding the note
- Locating the same C on the guitar, the piano and the voice.
Examples
Staff & keyboard
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The same name, C, in three different octaves. They share identity, but each is higher than the last. Listen to it climb from C to C.
Staff & keyboard
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A little figure —C, E, G— and the same figure an octave higher. It sounds the same in shape, but shifted up toward the treble.
Mini test
Check that you've got it.
0/6 answeredQuestion 1/6
How many different note names do we use before the series starts over?