Музыкада тон алмасуы

Change from one tonality to another

In music, modulation is the change from one tonality (tonic, or tonal center) to another. This may or may not be accompanied by a change in key signature (a key change). Modulations articulate or create the structure or form of many pieces, as well as add interest. Treatment of a chord as the tonic for less than a phrase is considered tonicization.

An enharmonic modulation takes place when a chord is treated 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 (fully) diminished seventh. Any dominant seventh or German sixth can be reinterpreted as the other by respelling the m7 or A6 chord tone (respectively) in order to modulate to a key a half step away (descending or ascending); if the fifth from root chord tone of a German sixth is omitted, the result is an Italian sixth. A diminished seventh chord meanwhile, can be respelled in multiple other ways to form a diminished seventh chord in a key a minor third (m3 as root), tritone (d5 as root) or major sixth (d7 as root) away. Where the dominant seventh is found in all diatonic scales, the diminished seventh is found only in the harmonic scale naturally; an augmented sixth is itself an altered chord, relying on the raised fourth scale degree. By combining the diminished seventh with a dominant seventh and/or augmented sixth, altering only one pivot note (by a half tone), it is possible to modulate quite smoothly from any key to any other in at most three chords, no matter how distant the starting and ending keys (be aware that only when modulating between key signatures featuring double sharps/flats may the need to respell natural notes enharmonically arise); however, this may or may not require the use of altered chords (operating in the harmonic minor without an augmented sixth would not) where the effect can be less subtle than other modulations. The following are examples used to describe this in chord progressions starting from the key of D minor (these chords may instead be used in other keys as borrowed chords, such as the parallel major, or other forms of the minor):

C–E–G–B (dim. 7th), C–E–G–B (lowering the root a semitone to a modulating dom. 7th), F–A–C (quasi tonic) leads to F major—a relative major modulation (though not enharmonic); but exactly the same progression enharmonically C–E–G–B, C–E–G–A (Ger. aug. 6th), E–G–B–E (quasi tonic) leads somewhat unexpectedly to E natural/harmonic minor—a half step modulation (ascending). C–E–G–B (dim. 7th), A–C–E–G (lowering the 7th a semitone and respelling as a modulating dom. 7th), D–F–A (quasi tonic) leads to the key of D major—a parallel modulation (though not enharmonic). Enharmonically: C–E–G–B, A–C–E–F (Ger. aug. 6th), C–E–G (quasi tonic) modulates to C minor—a major seventh modulation/half step descending. C–E–G–B (dim. 7th), C–E–G–B ≡ E–G–B–D (lowering the major third a half tone and respelling as a modulating dom. 7th), A–C–E (quasi tonic) leads to A major—a minor third and relative modulation (or tritone modulation if starting in D Major). Note that in standard voice leading practice, any type of augmented sixth chord favors a resolution to the dominant chord (see: augmented sixth chord), with the exception of the German sixth, where it is difficult to avoid incurring parallel fifths; to prevent this, a cadential six four is commonly introduced before the dominant chord (which would then typically resolve to the tonic to establish tonality in the new key), or an Italian/French sixth is used instead. In short, lowering any note of a diminished seventh chord by a half tone leads to a dominant seventh chord (or German sixth enharmonically), the lowered note being the root of the new chord. Raising any note of a diminished seventh chord by a half tone leads to a half diminished seventh chord, the root of which is a whole step above the raised note. This means that any diminished chord can be modulated to eight different chords by simply lowering or raising any of its notes. If also employing enharmonic respelling of the diminished seventh chord, such as that beginning the modulation in the above examples (allowing for three other possible diminished seventh chords in other keys), the versatility of this combination technique and the wide range of available options in key modulation become apparent. This type of modulation is particularly common in Romantic music, in which chromaticism rose to prominence. Other types of enharmonic modulation include the augmented triad (III+) and French sixth (Fr+6). Augmented triad modulation occurs in the same fashion as the diminished seventh, that is, to modulate to another augmented triad in a key: a major third (M3 as root) or minor sixth (A5 as root) away. French augmented sixth (Fr+6) modulation is achieved similarly but by respelling both notes of either the top or bottom major third (i. e. root and major third or diminished fifth and augmented sixth) enharmonically and inverting with the other major third (i. e. diminished fifth and augmented sixth becomes root and major third of the new Fr+6); either choice results in the same chord and key modulation (a tritone away), as the diminished fifth always becomes the new root.

Common tone modulation uses a sustained or repeated pitch from the old key as a bridge between it and the new key (common tone). Usually, this pitch will be held alone before the music continues in the new key. For example, a held F from a section in B major could be used to transition to F major. This is used, for example, in Schubert's Unfinished Symphony. "If all of the notes in the chord are common to both scales (major or minor), then we call it a common chord modulation. If only one or two of the notes are common, then we call it common tone modulation." Starting from a major chord, for example G major (G–B–D), there are twelve potential goals using a common tone modulation: G minor, G minor, B major, B major, B minor, C major, C minor, D minor, D major, E major, E major, E minor. Thus common tone modulations are convenient for modulation by diatonic or chromatic third.

[[File:Sequential modulation in Schubert, Sonata in E Major, movement III. png|thumb|350px|Sequential modulation in Schubert's Piano Sonata in E Major, D. 459, movement III Although a sequence does not have to modulate, it is also possible to modulate by way of a sequence. A sequential modulation is also called rosalia. 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.

Since modulation is defined as a change of tonic (tonality or tonal center), the change between minor and its parallel major or the reverse is technically not a modulation but a change in mode. Major tonic harmony that concludes music in minor contains what is known as a Picardy third. Any harmony associated with the minor mode in the context of major musical passages is often referred to as a borrowed chord, which creates mode mixture.

In certain classical music forms, a modulation can have structural significance. In sonata form, for example, a modulation separates 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 typically move to the relative major. Changes of key may also represent changes in mood. In many genres of music, 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.

The popularity of the key change varies with musical fashion over time. In Western popular music, from the 1960s to the 1990s, about one quarter of number one hits on the Billboard Hot 100 featured a key change, but only one number one hit in the 2010s had one.

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.