In music, modulation is the process of changing from one key to another. If a piece of music starts out in the key of F major but then changes, either immediately or gradually, to they key of Bb major, we would say it modulates from F major to Bb major. A piece is considered to be in a "key" if the root of the key is the tonic, also called "home" or the "gravitational center".
In some definitions, a modulation isn't considered to have taken place until the new key has been confirmed with a perfect authentic cadence. More loosely though, you have changed key if a new tonal center feels now like the tonic.
What is the purpose or point of modulation?
One reason is to add interest and variety to your music. Especially if you repeat the same sections many times, changing the keys will, at the very least, give your listener something interesting to hear.
The contrast of the first key with the second, or an increase or decrease in intensity, can be interesting even on a subtle level.
Modulations often provide a sense of forward propulsion and drive the music into new levels of energy. In the classical repertoire a majority of pieces modulate to the key of the dominant, and the introduction of an extra sharp (for example introducing the pitch F# to modulate from C to G major) can give the music lift and direction.
From a practical standpoint, a film composer might need to write a piece of music that fits between two already existing songs in different keys. The middle piece will need to smoothly transition from the key of the first piece to the key of the second. Or if there is no transition, the composer needs to at least be aware of the effect of a sudden change in key and make sure it is welcome.
So how do you modulate?
1. Direct Modulation
The simplest and most dramatic type is direct modulation. This is where the music changes key with no preparation.
In pop music this technique is often called a "truck driver's modulation" because it's like the song has kicked into another gear.
Barry Manilow uses the truck driver modulation often for the last chorus of his songs. For example Mandy is in Bb major for most of the song, and then it launches up into C major for the last repetition of the chorus.
The truck driver modulation is often criticized for being a cheap trick because it can be used as a way to repeat the last chorus without having to actually write anything new. Just knock it up a step or two and you're done!
A less scrutinized use of direct modulation in a song is for the bridge. A sudden change to a new key helps make the bridge feel like an exciting launch into a new section, which is different than repeating yourself only slightly higher.
In John Mayer's City Love, the main part of the song is in D major. By the time it gets to the bridge, we are already used to hearing the chorus resolve nicely into D.
But for the bridge, Mayer launches suddenly into the key of Bb (on the IV chord, Ebmaj7).
It's a deceptive cadence because we are set up to expect D but get something else instead. (Something very clever about it is that the melody note is still the expected D. It's just that instead of being the root of a D major triad like we expect, it's the maj7 of an Ebmaj7 chord.)
Direct modulation can be very useful for film composers.
As I mentioned before, a direct modulation can be very dramatic. It adds a sudden burst of energy to the music, which is naturally a useful technique if a score needs to make the film feel suddenly more exciting.
In this scene from Back to the Future III the score makes a sudden direct modulation six times in just the first minute alone!
- 0:15 modulates up a minor third
- 0:25 modulates up a minor third
- 0:35 modulates up a minor third again
- 0:41 modulates up a minor third again
- 0:52 modulates up a minor third again
- 1:00 modulates up a minor third again!
Also worth noticing is that Alan Silvestri is able to stretch the use of only the main Back to the Future motif and the Wild West motif, plus some filler material. Very little actual new musical material is needed to drive things forward, it's more about using the same material in constantly intensifying ways.
2. Parallel Modulation
Parallel modulation is when you change mode without changing the root. For example going from F major to F minor.
It's naturally very smooth because the tonic remains the same, but is also very colorful because the character of the music changes quite dramatically.
Mozart was very fond of parallel modulations, one example can be heard in his famous Rondo alla Turca.
The A section is in A minor, the B section is in A major. Notice how bright and triumphant the B section feels by suddenly lifting the mood from minor to major!
3. Pivot Chord Modulation
The smoothest way to modulate from one key to another is to use a pivot chord. A pivot chord is a chord that both keys share in common.
For example C major and G major share four chords in common: C, Em, G, and Am.
Any one of these chords can be used to transition smoothly from C major to G major. If you want G major to feel very firmly like a new key it is best to "confirm" it with an authentic cadence. This means at the very least a V-I progression.
In this example from Haydn's 99th Symphony, the opening theme modulates from Eb major to Bb major in the first eight bars.
Eb and Bb both share the chord Cm in common, which Haydn uses as the pivot chord. It acts as both vi in Eb and ii in Bb.
Here is the audio from the beginning, plus bars 5-8 of the score:
Pivot chord modulations are usually found in classical or instrumental music, less so in pop or songwriting contexts.
The closer they keys are related, the easier it is to find natural pivot chords.
As you can see C major and G major are only one sharp different; they are considered closely related. Similarly, C major and F major have all notes in common except for one flat, and share four chords in common: C, Dm, F, and Am.
C major and D major have a difference of two sharps, making them more distantly related. They only share two chords in common: Em and G.
You could use the Em as a pivot chord to modulate from C to D. It is both iii in C and ii in D.
C and Eb are different by three flats, so they are more remote. The don't actually share any chords in common.
To modulate to remote keys you need to implement some more advanced techniques, such as borrowing chords from parallel modes or using chords such as the Neapolitan 6. Since this is an introductory lesson, we'll save the more advanced modulations for another day!
Modulation is a powerful tool for taking your music from a single key center on to a more interesting tonal journey.
As a last listening example, here is Fawkes the Phoenix from John Williams. Rather than give you all the answers, listen for yourself and see if you can hear when the music modulates to a new key. What is the effect? At what moments does the music feel like it soars into new places?
Is changing keys a way you can introduce more energy and forward drive into one of your songs?
Share your thoughts and questions about modulation in the comments.