Modulation (music)

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Example of modulation from the tonic to the dominant.Play Modulation vocal music example duple labelled.png
Example of modulation from the tonic to the dominant. Play
Key signature change example: C major to C minor. Key change example.png
Key signature change example: C major to C minor.

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.

Contents

Modulation is the essential part of the art. Without it there is little music, for a piece derives its true beauty not from the large number of fixed modes which it embraces but rather from the subtle fabric of its modulation.

Charles-Henri Blainville (1767) [2]

Requirements

The quasi-tonic is the tonic of the new key established by the modulation. The modulating dominant is the dominant of the quasi-tonic. The pivot chord is a predominant to the modulating dominant and a chord common to both the keys of the tonic and the quasi-tonic. For example, in a modulation to the dominant, ii/V–V/V–V could be a pivot chord, modulating dominant, and quasi-tonic.

Types

Common-chord modulation

Common-chord modulation in the opening of Chopin's Prelude in C minor, Op. 28, No. 20.Play Chopin - Prelude in C minor opening modulation.png
Common-chord modulation in the opening of Chopin's Prelude in C minor, Op. 28, No. 20. Play
Common-chord modulation in Tchaikovsky's Album pour enfants (1887), Op. 39, No. 10, MazurkaPlay Common-chord modulation in Tchaikovsky, Mazurka Op. 39, No. 10.png
Common-chord modulation in Tchaikovsky's Album pour enfants (1887), Op. 39, No. 10, Mazurka Play
Common-chord modulation in the opening of Mozart's Sonata in D Major, K. 284, IIIPlay Common chord modulation in Mozart, Sonata in D Major, K. 284, III, m. 1-8.png
Common-chord modulation in the opening of Mozart's Sonata in D Major, K. 284, III Play

Common-chord modulation (also known as diatonic-pivot-chord modulation) moves from the original key to the destination key (usually a closely related key) by way of a chord both keys share: "Most modulations are made smoother by using one or more chords that are common to both keys." [7] For example, G major and D major have four triad chords in common: G major, B minor, D major and E minor. This can be easily determined by a chart similar to the one below, which compares triad 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.

G majorI
G
ii
Am
iii
Bm
IV
C
V
D
vi
Em
viio
Fo
D majorIV
G
V
A
vi
Bm
viio
Co
I
D
ii
Em
iii
Fm

Any chord with the same root note and chord quality (major, minor, diminished) can be used as the pivot chord. Therefore, chords that are not generally found in the style of the piece (for example, major VII chords in a J. S. Bach-style chorale) are also not likely to be chosen as the pivot chord. The most common pivot chords are the predominant chords (ii and IV) in the new key. In analysis of 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 heard either way.

Where an altered chord is used as a pivot chord in either the old or new key (or both), this would be referred to as altered common chord modulation, in order to distinguish the chromaticism that would be introduced from the otherwise diatonic method.

Enharmonic modulation

Modulation from D major to D major in Schubert's Op. 9, No. 14, D. 365, mm. 17-24, using the German sixth, in the new key, that is enharmonic to the dominant seventh in the old key.Play Schubert - op.9 D.365, mm.17-24 German sixth modulation.png
Modulation from D major to D major in Schubert's Op. 9, No. 14, D. 365, mm. 17–24, using the German sixth, in the new key, that is enharmonic to the dominant seventh in the old key. Play
Modulation from A minor to E minor in Schubert's Op.29, D. 804, I, mm.144-49, using vii : G# [?] D ([?] B [?] F )Play Schubert - op. 29, D.804, I, mm.144-49 enharmonic modulation.png
Modulation from A minor to E minor in Schubert's Op.29, D. 804, I, mm.144-49, using vii : G ≡ D (≡ B ≡ F ) Play

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. [10] 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):

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

Modulation between relative keys, C minor and E major, using a common tone, G, in Schubert's Op. 163 (D. 956).Play Schubert - Op.163 (D.956), i common-tone modulation.png
Modulation between relative keys, C minor and E major, using a common tone, G, in Schubert's Op. 163 (D. 956). Play
Common-tone modulation between chromatic mediants in Mozart's K.475Play Common tone modulation between chromatic mediants in Mozart K 475.png
Common-tone modulation between chromatic mediants in Mozart's K.475 Play

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." [13] [ self-published source? ]

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. [14] Thus common-tone modulations are convenient for modulation by diatonic or chromatic third.

Chromatic modulation

Chromatic modulation in Bach's Du grosser Schmerzensmann, BWV 300, mm. 5-6 (Play with half cadence, Play with PAC) transitions from F major to D minor through the inflection of C to C# between the second and third chords. Note that there is no common chord. Chromatic modulation in Bach BWV 300, m. 5-6.png
Chromatic modulation in Bach's Du grosser Schmerzensmann, BWV 300, mm. 5–6 ( Play with half cadence, Play with PAC) transitions from F major to D minor through the inflection of C to C between the second and third chords. Note that there is no common chord.

A chromatic modulation is so named because it occurs at the point of a chromatic progression, one which involves the chromatic inflection of one or more notes whose letter name, thus, remains the same though altered through an accidental. [15] Chromatic modulations are often between keys which are not closely related. [15] A secondary dominant or other chromatically altered chord may be 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 most often be in one voice.) For example, a chromatic modulation from C major to D minor:

C majorIV
F
V/ii
A
ii
Dm
D minori
Dm
(...)

In this case, the IV chord in C major (F major) would be spelled F–A–C, the V/ii chord in C major (A major) spelled A–C–E, and the ii chord in C major (D minor), D–F–A. Thus the chromaticism, C–C–D, along the three chords; this could easily be part-written so those notes all occurred in one voice. Despite the common chord (ii in C major or i in D minor), this modulation is chromatic due to this inflection.

The consonant triads for chromatic modulation are III, VI, II, iv, vii, and VII in major, and iii, vi, II, iv, ii, and vii in minor.

In the example pictured, a chromatic modulation from F major to D minor:

F majorI
F
V
C
D minorV
A
i
Dm
iv
Gm
V
A

In this case, the V chord in F major (C major) would be spelled C–E–G, the V in D minor (A major) would be spelled A–C–E. Thus the chromaticism, C–C–D, which is here split between voices but may often easily be part-written so that all three notes occur in one voice.

The combination of chromatic modulation with enharmonic modulation in late Romantic music led to extremely complex progressions in the music of such composers as César Franck, in which two or three key shifts may occur in the space of a single bar, each phrase ends in a key harmonically remote from its beginning, and great dramatic tension is built while all sense of underlying tonality is temporarily in abeyance. Good examples are to be found in the opening of his Symphony in D minor, of which he himself said (see Wikiquote) "I dared much, but the next time, you will see, I will dare even more..."; and his Trois Chorals for organ, especially the first and third of these, indeed fulfill that promise.

Phrase modulation

Phrase modulation in Mozart's Sonata in A major, K.331, III (Alla turca), mm. 6-10.Play Mozart - K.331, III, mm.6-10 phrase modulation.png
Phrase modulation in Mozart's Sonata in A major, K.331, III (Alla turca), mm. 6–10. Play

Phrase (also called direct, static, or abrupt) modulation is a modulation in which one phrase ends with a cadence in the original key, and the next phrase begins 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.

An unprepared modulation is a modulation "without any harmonic bridge", characteristic of impressionism. [17]

For example:

AEAFBF
A majorIVI
F majorIIVI

When phrase modulation comes at or near the end of a musical piece, it is referred to as a truck driver's gear change, especially in popular music.

Sequential modulation

Sequential modulation in Beethoven's Sonata Op. 53, movement IPlay Sequential modulation in Beethoven, Sonata Op. 53, movement I.png
Sequential modulation in Beethoven's Sonata Op. 53, movement I Play
Sequential modulation in Schubert's Piano Sonata in E Major, D. 459, movement IIIPlay Sequential modulation in Schubert, Sonata in E Major, movement III.png
Sequential modulation in Schubert's Piano Sonata in E Major, D. 459, movement III Play

"A passage in a given key ending in a cadence might be followed by the same passage transposed (up or down) to another key," this being known as sequential modulation. [19] 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.

Chain modulation

Sequential modulation through the circle of fifths in Quartet Op. 3, No. 3, IV, Hob. III:15, formerly attributed to Haydn (ca. 1840) Play Sequential modulation through the circle of fifths in Haydn, Quartet Op. 3, No. 3, IV.png
Sequential modulation through the circle of fifths in Quartet Op. 3, No. 3, IV, Hob. III:15, formerly attributed to Haydn (ca. 1840) Play

Distant keys may be reached sequentially through closely related keys by chain modulation, for example C to G to D or C to C minor to E major. [21] A common technique is the addition of the minor seventh after each tonic is reached, thus turning it into a dominant seventh chord:

DD7GG7CC7F
IV7IV7IV7I

Changes between parallel keys

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.

Common modulations

The circle of fifths drawn within the chromatic circle as a dodecagram Pitch class space star.svg
The circle of fifths drawn within the chromatic circle as a dodecagram
Modulation up a whole step at the end of "Because the Night" Play Truck driver's gear change Because the Night.png
Modulation up a whole step at the end of "Because the Night" Play

The most common modulations are to closely related keys (I, V, IV, vi, iii, ii). [23] V (dominant) is the most frequent goal and, in minor, III (relative key) is also a common goal. [24] Modulation to the dominant or the subdominant is relatively simple as they are adjacent steps on the circle of fifths. Modulations to the relative major or minor are also simple, as these keys share all pitches in common. Modulation to distantly related keys is often done smoothly through using chords in successive related keys, such as through the circle of fifths, the entirety of which may be used in either direction:

D – A – E – B/C – F/G – C/D – G/A – D/E – A/B – F – C – G – D

If a given key were G major, the following chart could be used:

CGD

From G (which is the given key), a musician would go P5 (a perfect fifth) above G (which is D) and also P5 below G (which is C).

From this, the musician would go to G major's relative minor which is E minor, and potentially to C major and D major's related minor as well (a musician who does not know the related minor for C and D major may also go P5 below or above E minor).

CGD
|||
AmEmBm

By using the relative minor keys one can find the specific key that the key can modulate into.

Many musicians use the circle of fifths to find these keys and make similar charts to help with the modulation.

Significance

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.

Popularity

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. [25]

Other types

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.

See also

Related Research Articles

<span class="mw-page-title-main">Major scale</span> Musical scale made of seven notes

The major scale is one of the most commonly used musical scales, especially in Western music. It is one of the diatonic scales. Like many musical scales, it is made up of seven notes: the eighth duplicates the first at double its frequency so that it is called a higher octave of the same note.

An altered chord is a chord that replaces one or more notes from the diatonic scale with a neighboring pitch from the chromatic scale. By the broadest definition, any chord with a non-diatonic chord tone is an altered chord. The simplest example of altered chords is the use of borrowed chords, chords borrowed from the parallel key, and the most common is the use of secondary dominants. As Alfred Blatter explains, "An altered chord occurs when one of the standard, functional chords is given another quality by the modification of one or more components of the chord."

A jazz scale is any musical scale used in jazz. Many "jazz scales" are common scales drawn from Western European classical music, including the diatonic, whole-tone, octatonic, and the modes of the ascending melodic minor. All of these scales were commonly used by late nineteenth and early twentieth-century composers such as Rimsky-Korsakov, Debussy, Ravel and Stravinsky, often in ways that directly anticipate jazz practice. Some jazz scales, such as the bebop scales, add additional chromatic passing tones to the familiar diatonic scales.

<span class="mw-page-title-main">Chord (music)</span> Harmonic set of three or more notes

In music, a chord is a group of three or more notes played simultaneously, typically consisting of a root note, a third, and a fifth. Chords are the building blocks of harmony and form the harmonic foundation of a piece of music. They can be major, minor, diminished, augmented, or extended, depending on the intervals between the notes and their arrangement. Chords provide the harmonic support and coloration that accompany melodies and contribute to the overall sound and mood of a musical composition. For many practical and theoretical purposes, arpeggios and other types of broken chords may also be considered as chords in the right musical context.

A secondary chord is an analytical label for a specific harmonic device that is prevalent in the tonal idiom of Western music beginning in the common practice period: the use of diatonic functions for tonicization.

<span class="mw-page-title-main">Augmented fifth</span> Musical interval

In Western classical music, an augmented fifth is an interval produced by widening a perfect fifth by a chromatic semitone. For instance, the interval from C to G is a perfect fifth, seven semitones wide, and both the intervals from C to G, and from C to G are augmented fifths, spanning eight semitones. Being augmented, it is considered a dissonant interval.

In music theory, an augmented sixth chord contains the interval of an augmented sixth, usually above its bass tone. This chord has its origins in the Renaissance, was further developed in the Baroque, and became a distinctive part of the musical style of the Classical and Romantic periods.

Chromaticism is a compositional technique interspersing the primary diatonic pitches and chords with other pitches of the chromatic scale. In simple terms, within each octave, diatonic music uses only seven different notes, rather than the twelve available on a standard piano keyboard. Music is chromatic when it uses more than just these seven notes.

In music theory, a dominant seventh chord, or major minor seventh chord, is a seventh chord, composed of a root, major third, perfect fifth, and minor seventh. Thus it is a major triad together with a minor seventh, denoted by the letter name of the chord root and a superscript "7". In most cases, dominant seventh chord are built on the fifth degree of the major scale. An example is the dominant seventh chord built on G, written as G7, having pitches G–B–D–F:

In Classical music theory, a Neapolitan chord is a major chord built on the lowered (flatted) second (supertonic) scale degree. In Schenkerian analysis, it is known as a Phrygian II, since in minor scales the chord is built on the notes of the corresponding Phrygian mode.

<span class="mw-page-title-main">Closely related key</span>

In music, a closely related key is one sharing many common tones with an original key, as opposed to a distantly related key. In music harmony, there are six of them: four of them share all the pitches except one with a key with which it is being compared, one of them share all the pitches, and one shares the same tonic.

The diminished seventh chord is a four-note chord composed of a root note, together with a minor third, a diminished fifth, and a diminished seventh above the root:. For example, the diminished seventh chord built on B, commonly written as Bo7, has pitches B-D-F-A:

In music, a minor seventh chord is a seventh chord composed of a root note, a minor third, a perfect fifth, and a minor seventh. In other words, one could think of it as a minor triad with a minor seventh attached to it.

<span class="mw-page-title-main">Tritone substitution</span> Music theory concept

The tritone substitution is a common chord substitution found in both jazz and classical music. Where jazz is concerned, it was the precursor to more complex substitution patterns like Coltrane changes. Tritone substitutions are sometimes used in improvisation—often to create tension during a solo. Though examples of the tritone substitution, known in the classical world as an augmented sixth chord, can be found extensively in classical music since the Renaissance period, they were not heard until much later in jazz by musicians such as Dizzy Gillespie and Charlie Parker in the 1940s, as well as Duke Ellington, Art Tatum, Coleman Hawkins, Roy Eldridge and Benny Goodman.

<span class="mw-page-title-main">Augmented sixth</span> Musical interval

In music, an augmented sixth is an interval produced by widening a major sixth by a chromatic semitone. For instance, the interval from C to A is a major sixth, nine semitones wide, and both the intervals from C to A, and from C to A are augmented sixths, spanning ten semitones. Being augmented, it is considered a dissonant interval.

In music theory, the half-diminished seventh chord is a seventh chord composed of a root note, together with a minor third, a diminished fifth, and a minor seventh. For example, the half-diminished seventh chord built on B, commonly written as Bm7(♭5), or Bø7, has pitches B-D-F-A:

A synthetic mode is a mode that cannot be derived from the diatonic scale by starting on a different note. Whereas the seven modes are all derived from the same scale and therefore can coincide with each other, synthetic modes work differently.

<span class="mw-page-title-main">Irregular resolution</span> Musical resolution to a chord other than the tonic

In music, an irregular resolution is resolution by a dominant seventh chord or diminished seventh chord to a chord other than the tonic. Regarding the dominant seventh, there are many irregular resolutions including to a chord with which it has tones in common or if the parts move only a whole or half step. Consecutive fifths and octaves, augmented intervals, and false relations should still be avoided. Voice leading may cause the seventh to ascend, to be prolonged into the next chord, or to be unresolved.

In music, harmonization is the chordal accompaniment to a line or melody: "Using chords and melodies together, making harmony by stacking scale tones as triads".

<span class="mw-page-title-main">Seventh (chord)</span> Musical chord

In music, the seventh factor of a chord is the note or pitch seven scale degrees above the root or tonal center. When the seventh is the bass note, or lowest note, of the expressed chord, the chord is in third inversion.

References

  1. Boston Academy of Music, Lowell Mason (1836). The Boston Academy's Collection of Church Music, pp. 16–18. Fourth edition. J. H. Wilkins and R. B. Carter.
  2. Forte, Allen (1979). Tonal Harmony in Concept & Practice, p. 265. ISBN   0-03-020756-8.
  3. 1 2 3 Forte (1979), p. 267.
  4. Benward and Saker (2009). Music in Theory and Practice, Vol. II, p. 214. ISBN   978-0-07-310188-0.
  5. Forte (1979), p. 307.
  6. Benward and Saker (2009), p. 244.
  7. Forte (1979), p. 305.
  8. Benward & Saker (2009), pp. 214–15.
  9. Benward & Saker (2009), p.220.
  10. "Enharmonic Reinterpretation" (PDF). Feezell, M. Retrieved 2016-04-05.
  11. Meyer, Leonard B. (1989). Style and Music: Theory, History, and Ideology, p. 299. ISBN   9780226521527.
  12. Kostka, Stefan and Payne, Dorothy (1995). Tonal Harmony, p. 321. McGraw-Hill. ISBN   0-07-035874-5.
  13. Briggs, Kendall Durelle (2014). The Language and Materials of Music, p. 198. Lulu.com. ISBN   9781257996148.[ self-published source ]
  14. Kopp, David (2006). Chromatic Transformations in Nineteenth-Century Music, p. 50. Cambridge University Press. ISBN   9780521028493. After Marx, Adolph Bernard. Theory and Practice (1837). Trans. Saroni.
  15. 1 2 3 Benward and Saker (2003). Music: In Theory and Practice, Vol. I, p. 245. Seventh Edition. ISBN   978-0-07-294262-0.
  16. Benward and Saker (2003), Vol. I, p. 244.
  17. Reti, Rudolph (1978). Tonality, Atonality, Pantonality. Westport, CT: Greenwood Press. ISBN   0-313-20478-0.
  18. 1 2 Forte (1979), p.319.
  19. Heussenstamm, George (2011). Hal Leonard Harmony & Theory – Part 2: Chromatic. ISBN   9781476841212.
  20. Forte (1979), p.320.
  21. Jones, George T. (1994). HarperCollins College Outline Music Theory, p. 217. ISBN   0-06-467168-2.
  22. "Prelude to Musical Geometry", p. 364, Brian J. McCartin, The College Mathematics Journal, Vol. 29, No. 5 (Nov., 1998), pp. 354–70. (abstract) (JSTOR).
  23. Benward & Saker (2003). Music: In Theory and Practice, Vol. I, p. 243. 7th edition. McGraw-Hill. ISBN   978-0-07-294262-0. "Most modulations occur between closely related keys, which are those keys that differ by no more than one accidental in the key signature."
  24. Forte (1979), p. 269.
  25. All Things Considered (November 25, 2022). "Why the key change has disappeared from top-charting tunes".

Further reading