Key Signatures and the Ladder of Fifths

Hello and welcome back. I'm Joseph Hoffman.
Today is a very epic day because we're unlocking the secrets of key signatures.
We've already learned about time signatures.
Now it's time to start using key signatures.
A key signature is placed right before the time signature, and tells you which notes in this piece will get
automatically sharped or flattened.
Let's look back at a song we learned in an earlier unit "Au Claire de la Lune".
Remember all those flats?
Well, imagine you had to write this song down by hand.
All those flat symbols can get kind of annoying to write.
At least that's what musicians thought hundreds of years ago.
So they invented a shortcut called a key signature.
To create a key signature, you first need to know what key you're in.
For "Au Clair de la Lune", we're in the key of A-flat major,
and we know A-flat major has four flats: A-flat, B-flat, D-flat, and E-flat.
You simply write all the sharps or flats that you need at the start of the staff line,
and that tells the player to automatically flat those specific notes.
So with the key signature, you don't need to write all the flats or sharps in front of the notes anymore.
They happen automatically.
Look how much cleaner the music looks!
Pretty!
Remember, "Black Snake" in the key of D major?
D major needs an F-sharp and also a C-sharp for the V7 chord.
So we can also rewrite this one with a key signature.
Voila!
So now you know two ways composers can tell you to play a sharp or flat.
They can place it right in the flow of the music immediately in front of the note,
or they can place it in a key signature at the beginning of the staff
to automatically sharp or flat that particular note.
For example, with this key signature, since the sharp is on the F line,
you would sharp every F on this entire staff whether it's this F,
or this F.
But how does a composer choose which sharps or flats to place in the key signature,
and why do they always follow a special zigzag pattern?
Those are the questions we're going to answer today.
For this lesson, I recommend that you print out the latter of fifths theory page as part of the materials from this unit
so you can fill it out along with me.
Pause the video if you need a moment to print that out and grab a pencil.
Otherwise, let's come to the piano to unlock the secrets of key signature.
The easiest key signature of all is C major, because it's all white keys. We don't need any sharps or flats.
To build any one octave scale, you recall from a previous lesson we just need these two tetrachords.
Each one with a half step in the top position of the tetrachord.
Now, today we're going to keep track of each new key signature that we discover.
Starting with C major, and to do this,
we're going to unveil, drum roll...
Behold the ladder of fifths.
This is a handy little tool that we will use to figure out all the keys that have sharps in it.
So let's get started down at the bottom.
Now if you get the printable materials for this unit, you'll be able to print this out and do this along with me.
I'm starting at the bottom of the ladder with C major,
and this is the first rung of the ladder because C major has zero sharps in the key signature.
So this will just be blank.
If you come across a piece of music with nothing in the key signature, chances are you're in the key of C major.
So now as we go up the ladder, we're going up fifths.
Can you tell me what would a fifth above C be?
If you said G, you're correct.
So, next we get to figure out how many sharps in the key of G major using the one octave scale.
Let's come back to the piano to figure that out.
All right, so let's figure out how we would build a G major one octave scale.
Using these tetrachords, does this tetrachord look like a major tetrachord?
The answer is yes because we do have a half step here
in this top position between the third and fourth note, or MI and FA.
Now what about this tetrachord? Are we good here.
No, not quite.
We don't have a half step here, so we would need to take this F,
and make it F-sharp,
and that now gives us a half step between TI and DO.
So this would be the key of G major. Let's try to play it.
Okay, left hand fingers 5 4 3 2
on these four notes, and then right hand 2 3 4 5
with finger 4 on that F-sharp.
Get in position.
No thumbs needed, and let's sing the solfège for G major. Ready, go.
DO RE MI FA SO LA TI DO. Now let's step down.
DO TI LA SO FA MI RE DO
Now say the letter names, ready go: G A B C D E F-sharp G. Now step down.
G F-sharp E D C B A G.
As always you can press pause to practice that a little bit more if you need to,
but otherwise let's keep going.
So let's mark down what we ...