Today we will learn another important topic on music theory: key modulation. Modulation is the process of changing a key to another one, which implies to change the key signature, melody and chords from the original to the destination key.
In a very simple way, when we modulate a song, we are applying a given interval over its melody and harmony structure from one key to another.
Let’s consider the following example:
Notice that this example is written in the key of C, and it has four measures. It has a melody and a sequence of chords.
Let’s say now that we want to modulate this song to D. How would we do that?
Remeber that modulation is all about applying a fixed interval to the whole song structure.
First, we need to find out the interval between the original and the destination key. So, to go from C to D we need to go up a whole tone. That means that we will modulate chords, melody and key signature from the original key a whole tone up. Observe:
Notice the new key signature, which indicates a key of D.
Also, notice that the whole melody was modulated by a whole tone up, as well as the chords.
So, Example 2 is Example 1 modulated one whole tone up.
One super important note: we never change the chord type, ever. So, a major chord in the original key will continue to be a major chord in the destination key. A minor 7th chord will keep being a minor 7th chord and so on.
So, when we modulate a song, all we need to find out is the interval between the original key and the destination key. Once we find it, we will apply the interval to all the song structure: key signature, melody and chords.
Now, how we modulate the original example to the key of F?
It’s exactly the same process. We just find out the interval between C and F, and then we apply it to write the song in the new key (F):
As you might have already noticed, there’s a perfect 4th between C and F. So, we will modulate key signature, melodies and chords a perfect 4th up:
Notice that the chord types are exactly the same – we just modulate it a perfect 4th above.
That’s it! In the next lesson, we will practice modulation a little more.