From Academic Kids
In music, modulation is most commonly the act or process of changing from one key (tonic, or tonal center) to another, also known as a key change. This may or may not be accompanied by a change in key signature. Modulations articulate or create the structure or form of many pieces, as well as add interest.
Types of modulation
There are several different types of modulation -- modulations may be prepared or unprepared, smooth or abrupt. It is smoother to modulate to more closely related keys than to keys further away. Closeness is determined by the number of notes in common between keys, which provides more possible pivot chords, and their closeness on the circle of fifths. A modulation is often completed by a cadence in the new key, which helps to establish it. Brief modulations are often considered tonicizations.
Common chord modulation
Common chord modulation moves from the original key to the destination key (usually a closely related key) by way of a chord both keys share. For example, G major and D major share 4 chords in common: GMaj, Bmin, DMaj, Emin. This can be easily determined by a chart similar to the one below, which compares chord qualities. The I chord in G Major—a G major chord—is also the IV chord in D major, so I in G major and IV in D major are aligned on the chart.
Any chord with the same root note and chord quality can be used as the "pivot chord." However, chords that are not generally found in the style of the piece (for example, major VII chords in a Bach-style chorale) are also not likely to be chosen as the pivot chord. When analyzing a piece that uses this style of modulation, the common chord is labeled with its function in both the original and the destination keys, as it can be seen either way.
An enharmonic modulation is when one treats a chord as if it were spelled enharmonically as a functional chord in the destination key, and then proceeds in the destination key. There are two main types of enharmonic modulations: dominant seventh/augmented sixth, and diminished seventh -- by respelling the notes, any dominant seventh can be reinterpreted as a German or Italian sixth (depending on whether or not the fifth is present), and any diminished seventh chord can be respelled in multiple other ways to form other diminished seventh chords.
(Examples: C-E-G-Bb, a dominant 7th, becomes C-E-G-A#, a German sixth. C#-E-G-Bb, a C# diminished seventh, can also be spelled as E-G-Bb-Db, an E diminished seventh, G-Bb-Db-Fb, a G diminished seventh, and Bb-Db-Fb-Abb, a Bb diminished seventh.)
Common-tone modulation uses a sustained or repeated pitch from the old key as a bridge between it and the new key. Usually, this pitch will be held alone before the music continues in the new key. For example, a held F from a section in Bb major could be used to transition to F major.
A chromatic modulation is so named because a secondary dominant or other chromatically altered chord is used to lead one voice chromatically up or down on the way to the new key. (In standard four-part chorale-style writing, this chromatic line will be in one voice.) For example, a chromatic modulation from C major to d minor:
In this case, the IV chord, FM, would be spelled F-A-C, V/ii, AM, A-C#-E, and the ii chord, dm, D-F-A. Thus the chromaticism, C-C#-D, along the three chords; this could easily be partwritten so those notes all occurred in one voice.
Phrase (direct, abrupt) modulation
Phrase (also called direct or abrupt) modulation is a modulation in which one phrase ends with a cadence in the original key, and begins the next phrase in the destination key without any transition material linking the two keys. This type of modulation is frequently done to a closely related key -- particularly the dominant or the relative major/minor key. A common device in popular music, the "truck driver's gear change," is an abrupt modulation, usually to the key a semitone above, typically used to provide an "emotionally uplifting" finale.
Abrupt modulation is also common in forms with sharply delineated sections, such as theme and variations and many dance forms.
Sequential modulation (rosalia)
It is also possible to modulate by way of a sequence. The sequential passage will begin in the home key, and may move either diatonically or chromatically; harmonic function is generally disregarded in a sequence, or, at least, it is far less important than the sequential motion. For this reason, a sequence may end at a point that suggests a different tonality than the home key, and the composition may continue naturally in that key.
A sequence does not have to modulate; a modulating sequence is known as a rosalia.
The most common modulations are to closely related keys. Modulation to the dominant or the subdominant is relatively easy as they are adjacent steps on the circle of fifths. Modulations to the relative major or minor are also easy, as these keys share all pitches in common. Modulation to distantly related keys will often be done smoothly through successive related keys, such as through the circle of fifths, the entirety of which may be used:
- C - G - D - A - E - B - F# - C# - G# - D# - A# (B flat) - F - C
Significance of modulation
In certain classical music forms, a modulation can have structural significance. In sonata form, for example, a modulation divides the first subject from the second subject. Frequent changes of key characterize the development section of sonatas. Moving to the subdominant is a standard practice in the trio section of a march in a major key, while a minor march will move to the relative major.
Changes of key may also represent changes in mood; many composers associate certain keys with specific emotional content, but in general, major keys are cheerful or heroic, while minors are sad and somber. Moving from a lower key to a higher often indicates an increase in energy.
Change of key is not possible in the full chromatic or the twelve tone technique, as the modulatory space is completely filled; i.e., if every pitch is equal and ubiquitous there is nowhere else to go. Thus other differentiating methods are used, most importantly ordering and permutation. However, certain pitch formations may be used as a "tonic" or home area.
Other types of modulation
Though modulation generally refers to changes of key, any parameter may be modulated, particularly in music of the 20th and 21st century. Metric modulation (known also as tempo modulation) is the most common, while timbral modulation (gradual changes in tone color), and spatial modulation (changing the location from which sound occurs) are also used.
Modulation may also occur from a single tonality to a polytonality, often by beginning with a duplicated tonic chord and modulating the chords in contrary motion until the desired polytonality is reached.
- Theory on the Web: Modulation (http://www.smu.edu/totw/modulate.htm)
- Modulation Types for Musical Analysis (http://utminers.utep.edu/charlesl/modulation.html)
- The Truck Driver's Gear Change Hall of Shame (http://www.gearchange.org)
- mute. (music theory on the web) - modulation or change of key (http://www.uta.fi/mute/english/har21.htm)
- A generalized system for musical modulation (http://home.datacomm.ch/straub/mamuth/modul/index_e.html)