School of Synthesis Modern Music Theory tutor Shaun Keyt explains Key Modulation in a way we can all understand it!
The Key of your track is the Scale you select for it's melodic elements. It can determine the musical character and melodic environment of your Track. A Key has two components: Tonic Note and Mode. If your track is in the Key of A Natural Minor, the Tonic Note is A and the Mode is Natural Minor.
By changing or "modulating" your Track's Key midway, you can give your Track a new sense of energy. This modulation can provide a new harmonic character in which the melodic elements can be replayed with new interest and provide you, as the Composer, with a new palette of notes and chords to play with.
Once you’ve decided to use Key Modulation, you’ll need to select which Key you’ll modulate into. All Keys are related and these relationships are represented by the Circle of Fifths. In the following diagram, the closer a destination key is to the starting key, the smoother the transition or modulation process will sound. This occurs because there will be only one note difference between two Keys which are next to each other in the chart. For example, the Keys of C major and G Major are next to each other in the Circle of Fifths chart. This is because the only note in the G major scale that's not in the C major scale is F#. The notes in the C major scale are C, D, E, F, G, A, B and the notes in the G major scale are G, A, B, C, D, E, F#. The further away two Keys are from each other in the Circle of Fifths, the more notes that will be different between the starting and destination Key. When selecting your destination Key, have in mind how much of an impact you want this change to have on your Track. You might be looking for a subtle change in mood or you might be looking for a noticeable lift to your Track.
How you move between these two Keys is the process of Key Modulation. There are many ways of completing this transition and we’ll look at some of them.
Direct modulation is where you literally change immediately into the new destination Key. It is the most abrupt and brutal method of modulation because there is no preparation or smooth transition to the process. For example, to modulate from C major to A major, the chord progression of C F G in the Key of C major would be immediately followed by the chord progression of A D E.
A smoother method of modulation is Diatonic Common Chord Modulation. With this, you use a chord which is common to both Keys for the transition. This chord is known as a Pivot Chord and allows for the modulation to occur more gradually. Let’s look at an example of moving from the Key of C Major to D Major. An initial chord progression of C F G could be immediately followed by the chords of G A D where the G major chord would act as a Pivot Chord. The Pivot Chord is like a middle ground between the two Keys which allows for a smoother modulation.
You may want to move between two Keys where there is no common chord. If the two Keys share a chord with the same Root Note but different Mode, you could alter the mode of that chord to fit the new Key. This process is called Altered Common Chord Modulation. An example of this would be if you modulated from the Key of C major (containing the chords: C Dm Em F G Am Bdim) to the Key of E major (containing the chords: E F#m G#m A B C#m D#dim). The chord with the Root Note of A is in both Keys, so by playing it as A minor in the Key of C major, you could modulate into E Major by playing the A minor chord as A major. Staying on the same Root Note as the modulation occurs is another example of providing a smoother Key change.
Key Modulation can, without careful preparation, sound obvious and clunky. An example of this might be songs where the chorus is sung in one key and then immediately repeated in a new Key (Direct Modulation). But, when the Key Modulation is completed carefully with a smooth process of transition such as Common Chord Modulation, it can provide a musical moment which has a new spark of life and interest.
Shaun Keyt is School of Synthesis' expert music theorist and is the tutor in the popular Modern Music Theory course.