A note is a single musical sound with a definite pitch: how high or low it sounds. Western music uses only twelve notes, and everything is built from them. Almost every rock or pop song you have ever heard uses just these twelve.
Seven of the twelve notes are the natural notes. They are named with the first seven letters of the alphabet, A to G. Together these seven notes make up a scale (a set of notes played in order), one that has been used in Western music for centuries. We'll look at scales later. Click a note to hear it:
After G, the letters simply start again at A. The new A sounds like the first one, only higher. The distance from a note to the next note with the same name is called an octave.
Every sound is a vibration. Its frequency is how many times per second it vibrates, measured in hertz (Hz). A higher frequency sounds higher. The A an octave up has exactly double the frequency of the A below it: 440 Hz becomes 880 Hz. This is true for every note, and it works both ways: the same note an octave lower has exactly half the frequency.
Played one after another, these notes sound just right. But the distance between them is not always the same. Below you see how much higher each note is than the one before. From B to C and from E to F the step is only about half as big as the others: A to B goes up about 12%, B to C only about 6%. Don't worry about the exact numbers. (We use percent because our ears hear pitch steps as ratios, not as a fixed number of Hz.)
The small step is a half step (also called a semitone). The big step is a whole step: two half steps. We write whole steps as W and half steps as H. There is a half step from B to C and from E to F. Between all the other natural notes there is a whole step.
A whole step leaves room for one more note in the middle. These in-between notes are the accidentals. There are five whole steps between the natural notes, so there are five accidentals. Seven natural notes plus five accidentals make twelve.
Each accidental is named after a natural note next to it, so it has two names. Named after the note below it, it is a sharp (♯): a half step higher than that note. Named after the note above it, it is a flat (♭): a half step lower than that note. The ♯ and ♭ signs are called accidentals, too.
For example, the note between A and B is A sharp (A♯) or B flat (B♭). Which name to use depends on the situation; more on that later. Either way, it is exactly the same note. Two names for the same sound are called enharmonic.
From B to C and from E to F there is no accidental: a half step leaves no room for another note. Sometimes a natural note gets a second name, too. For example, B can also be called C♭. C♭ is not a note between B and C. It is exactly the same note as B, named from the note above. We'll see why that happens when we build scales.
Rarely, a note even needs two signs. A double sharp (𝄪) raises a note by two half steps, and a double flat (𝄫) lowers it by two. So F𝄪 is the same note as G, and B𝄫 the same as A. Why write F𝄪 instead of G? In a scale every letter has its own place, and sometimes the right letter needs two signs to reach the right note. You'll meet them in a few scales and chords (several notes played together) later on.
The seven natural notes and the five accidentals give us all twelve notes. Here they are with the sharp names:
And here with the flat names. They are still exactly the same twelve notes, just named differently:
All twelve notes in a row, each a half step above the last, make the chromatic scale. It is the basis for all Western music.
But why twelve notes, and why these twelve? The next page shows where they come from.
Next: Why Twelve Notes?