Tonal Modulation

Hey so here's a short talk about tonal modulation. Modulating is the process of changing keys or modes, when used appropriately it can really enhance a piece of music. We're going to focus on more tonal modulation, which discusses a key change but the mode remains either major (ionian) or minor (aeolian) and get to modal modulation another time.

You can modulate however you want whenever you want just by playing a new melody in the middle of an old one, essentially playing a new song in the middle of an old one. Since it can be very hard for your listener to process the key change as more than dissonance, here are 3 common types of key changes.

1. Up one semi/whole tone.

This is a very common modulation in pop and showtunes. Usually at the end of a song, to show off the singer's range, the song will ascend a whole tone (though sometimes a semitone) right before the final chorus. This kind of modulation is great if you really want to show off your diva but they're really tacky, use it with caution.

2. Up a P5th / Down a P4th

Another very common type of modulation is to the dominant of the key either up a perfect 5th or down a perfect 4th. This is more common in blues and classical music. It's fun and effective when used sparingly and it isn't near as tacky as the 1st kind. This kind of modulation can be done directly by beginning a new line in a new key without too much clash but it can also be prompted using applied dominance.

One way to make the listener anticipate the key change is to use V of V (i.e. II in major, D major in the key of C) to "tonicize" the dominant chord before you change keys. You can do this effectively by using II at the end of a chord progression in place of V, consider:

| C | F | C | G |
| Am | F | Dm | G |
| C | C7 | F | Am |
| C | F | C | G |

| C | F | C | G |
| Am | F | Dm | G |
| C | C7 | F | Am |
| C | F | C | D / D7 |

| G | C | G | D |...

Musicians often call this kind of chord change a "two - five" because the progression uses II to introduce V. Also possible, though less common is to go II - v with v in minor instead of major. This kind of modulation is both modal and tonal. The song changes mode as well as key (tonality).

3. The third way to common way change keys is to change major to its relative minor and the back. This kind of modulation is more common in classical and jazz where the music may have a "minore" (minor) or "majiore" (major) section, sometimes songs will have a verse in one key and the chorus in its relative major/minor. Usually this kind of modulation modulates back to the original key.

Transitioning to a relative major or minor key is pretty smooth and easy. You can usually more or less just substitute the major for the minor and the dominants and achieve a decent progression in the new key. The chords in one key usually have a very similar function in the new key. Consider these chords and their functions in the key of C major:

C - I (tonic)
Dm - ii (subdominant)
D - II (applied dominant)
Em - iii (subdominant, tonic)
E - III (dominant, subdominant, tonic)
Fm - iv (subdominant)
F - IV (subdominant)
G - V (dominant)
Am - vi (subdominant, tonic)
Bdim - viio(dominant)

Now consider what function these chords have relative to the key of Am:

C - III (subdominant, tonic)
Dm - iv (subdominant)
D - IV (subdominant)
Em - v (subdominant)
E - V (dominant)
Fm - vi (subdominant)
F - vi (subdominant)
G - bVII (subdominant)
Am - i (tonic)
Bdim - ii (subdominant)

If you compare the two you can see that every chord except D (II, IV), and G (V, bVII) retained at least one of it's functions from the previous key. This means our chord progressions don't have to change very much to have a key change. Consider:

| C | F | C | G |
| Am | F | Dm | G |
| C | C7 | F | Am |
| C | F | C | G |

| Am | F | C | G |
| Am | F | Dm | E |
| Am | Am7 | F | C |
| Am | F | C | E |

This should make decent sense and all I changed were the C's, Am's, and G's when it made sense to to better satisfy the required chord function in a line. This kind of modulation is both modal and tonal.

Next time we'll focus on modal modulation.

Nice job, keep 'em comin'