The note alphabet & octaves

When a man's and a woman's voice sing the same line, everyone hears it immediately: same note, just higher. That distance is called an octave, and the two notes are related closely enough that they share a name.

There are only seven names: A · B · C · D · E · F · G. After that the series starts over at A, one octave higher, in both directions. (German-language sources write H for what is called B internationally; this guide uses B throughout.)

Seven letters, but twelve notes — there's another note between most of the letters. Where it comes from is covered in the next section. What matters first is the number: after twelve notes, everything repeats.

The reason for the octave relationship is measurable: the higher note vibrates exactly twice as fast. A 2 : 1 ratio is the closest relationship two notes can have, and the ear nearly merges them. Thinking in distances carries the whole guide — every melody and every chord is made of distances like this one.

So the entire system is twelve notes repeating upward and downward. A small supply, not an open field.