Measuring half steps and whole steps

- [Instructor] A half step is the distance from any key to the very next key above or below. It can be a black key or a white key. A whole step is equal to two half steps. Skip one key, either a black key, or a white key. A tetrachord is a series of four notes, having a pattern of whole step, whole step, half step. The notes of a tetrachord must be in alphabetical order, and must also have the whole step, whole step, half step pattern.

Let's take a look at some half steps and whole steps on the keyboard. If you start on C, and go up a half step, you'll play the black key C-sharp. Now let's look at D, and go down a half step. You're playing D-flat. Notice that this black key can have two names, C-sharp or D-flat, and that's true for any black key on the keyboard. Now, a whole step is two half steps put together.

So if we want to play C and go up a whole step, we'll skip C-sharp, that's a half step, and we'll go to D. A whole step up from D, is E. Now, what happens if you start on a black key, and you want to go up a whole step? Let's start on F-sharp. We can also call this G-flat. If we go up a whole step from there, we'll skip the white key, that'll be our half step, and we'll go to G-sharp, we can also call it A-flat, and from there, if we go up another whole step, we're on A-sharp or B-flat.

Now a tetrachord is a series of four notes. And it's a pattern that uses the half and whole steps that we've just learned. A tetrachord starting on C, from there you would go up a whole step to D, another whole step to E, and then a half step to F.