This is the first part in my series about music theory. In this part, we'll cover the octave.
Remember: You can hit the notes to play their sounds. If you're on iPhone, turn your ringer on to enable sound.
In western music, there are typically 12 unique musical notes that correspond with a sound. On a piano, this consists of 7 white keys: C, D, E, F, G, A, and B in addition to 5 black keys.
Each black key is placed between two white keys and therefore has two names. One of a black key's name is the name of the previous white key, paired with a # (called a sharp). The other name is the name of the next white key, paired with a b (called a flat). So, the black key between the C and D keys can be called C# (C Sharp) or Db (D flat). Sharp / flat notes are sometimes referred to as accidentals, which is a concept that might not make much sense 'til later in the series.
For the sake of simplicity, I'll refer to black keys by one of their names at a time instead of both.
Any sequence of 7 consecutive (touching) white keys are called an octave (pronounced "octiv"). This is because the 8th note in the sequence is the same note as the 1st note in the sequence. So, the next note after the B is another C!
The two highlighted notes are both C's. They're an octave apart, so the C on the right has a higher pitch, but they're fundamentally the same note. As a matter of fact, if you're on a mobile device, try to press both keys simultaneously. You should be able to hear both notes, but they'll have a kind of cohesion that makes them sound the same.
These highlighted notes are all in the same octave.
The first note in an octave doesn't actually have to be a C; that's just a common practice in modern music theory. You can start your octaves with A, G, or even D# if you want, but when reading and discussing music you'll typically find C notes to be the center of an octave.
Technically, an infinite amount. The frequency of any note is simply a multiple of the same note in any other octave. So, technically the frequency can increase toward infinity (infinite octaves) or decrease toward 0. The limit for us is the range of frequencies that we can hear.
They're identical, but what you call it depends on the key you're in. We'll talk about those in a later lesson. For now, they're interchangeable.
In the next post, we'll cover musical scales.