Wikipedia defines musical modulation as the act or process of changing from one key (tonic or tonal center) to another. This may or may not be accompanied by a change in key signature. So, any time the tonal center or key of a piece of music changes, a modulation has occurred. Sometimes composers clearly label this change by changing the key signature in the sheet music at the point of modulation. Other times composers will retain the original key signature and use accidentals to achieve the modulation. Modulations achieved by use of accidentals may require more detailed analysis to discover.
The two main categories of musical modulation are diatonic and chromatic modulation. In diatonic modulation, the transitional device (chord or pitch) used to modulate is diatonic to both the old and new key. In chromatic modulation the transitional device (chord or pitch) used to modulate is chromatic to the old key and leads to the new key. Since both chords and pitches can be used as transitional devices, there are two types of diatonic modulation called common (or pivot) chord and common tone modulation. I discussed these two types of modulation in detail last week. There is also another type of modulation called enharmonic modulation which involves the enharmonic respelling of pitches. This type of modulation can be categorized as either diatonic or chromatic depending on how we view the respelled pitch. I will cover this and chromatic modulation in today’s lesson.
The two most common uses of enharmonic modulation are dominant seventh / German +6 and fully diminished seventh chord modulation. With the fist type, a dominant seventh chord is respelled so that the seventh is now an augmented sixth. This transforms the chord into a German +6 which resolves to the V of the key one half step below the original key.
There are several methods of modulation which result in abrupt and dramatic changes in key. For example, phrase modulation is a method in which a musical phrase is ended in the original key and then the next phrase just begins in the new key. In sequential modulation, a repeating musical sequence is stated in the original key and then in the new key. In chain modulation people cycle through harmonic patterns (circle of fifths is most common method) until they reach the new destination key. Finally, in parallel key modulation people suddenly shift from a major key to its parallel minor (or from minor to major). The existence of the same tonic between the major and minor keys helps to solidify this type of transition.
Another example of chromatic modulation is the use of parallel shifts within chord progressions. While traveling to a chord that is normally major (within the given key signature), we could shift that chord to the parallel minor and then continue the progression to a new key. This shift can also be done on minor chords (shifting to major). In addition, chords can be shifted to diminished harmonies which lead to other keys.
This Learning Music With Ray video discusses musical modulation. In it, I review the meaning and aspects of modulation as they relate to harmonic structure and key center. I list the various types of modulation found in music. I then continue our discussion from last week, covering the other two types of modulation in detail. I provide musical examples throughout the discussion.