Notes & Octaves
What is an octave, and why is every C on the piano called C? Play the highlighted keys, then hear how doubling a frequency gives you the same note — and how 12 note names fill the space between.
Every orange key below is called C. Play them one by one — they sound like the same note standing at different heights.
The octave: same name, different height
The distance from one C to the next is an octave. They share a name because your ear genuinely hears them as the same note — the higher one vibrates exactly twice as fast (a 2:1 frequency ratio).
Prove it by ear: ×2 jumps up an octave, ×½ drops down one, and the note name never changes.
The 12 notes inside an octave
Back to the keyboard: between two Cs there are 12 different notes — 7 white keys (C D E F G A B) plus 5 black keys. Black keys borrow their names from their neighbors: the black key just right of C is C# (C sharp), and the very same key is also Db (D flat) — two spellings, one sound. After 12 notes the names start over, just one octave higher. All of music is built on this loop of 12.
Quiz
Each option plays a pair of notes. Listen to both: which pair is an octave?