Modulation

             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.  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 more detail next week.

            Common (or pivot) chord modulation utilizes a chord that is common to both keys as a device to modulate from one key to the next.  When utilizing this technique, the composer (or musician) travels through a chord progression until arriving at the common chord.  He/she then instantly shifts his/her analysis of that chord by relating it to the new key and finishing the progression in the new key.  The included video provides several musical examples of this.

            Common tone modulation utilizes a pitch that is common to both keys.  This pitch is either sustained or sounded repeatedly, allowing the harmonic structure to change from a chord in the original key to a chord in the new key.  Since both chords share the common tone, the transition is perceived as smooth. The included video provides a musical example of this.

            Understanding the use of common chord and common tone modulation will help us to be able to identify these techniques when they occur in everyday musical examples.  Knowledge of these techniques can also be used in musical performance when playing open styles of music (jazz, rock, pop, gospel or worship) from lead sheets.  In these styles, musicians often throw in modulations in order to increase the intensity of the song, or smoothly transition from one song to the next in a set list.

This Learning Music With Ray video discusses musical modulation.  In it, I explain 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 discuss two types of modulation in detail, providing musical examples throughout the discussion.