Tone cluster
A tone cluster is a musical chord comprising at least three adjacent tones in a scale. Prototypical tone clusters are based on the chromatic scale and are separated by semitones. For instance, three adjacent piano keys struck simultaneously produce a tone cluster. Variants of the tone cluster include chords comprising adjacent tones separated diatonically, pentatonically, or microtonally. On the piano, such clusters often involve the simultaneous striking of neighboring white or black keys.
The early years of the twentieth century saw tone clusters elevated to central roles in pioneering works by ragtime artists Jelly Roll Morton and Scott Joplin. In the 1910s, two classical avant-gardists, composer-pianists Leo Ornstein and Henry Cowell, were recognized as making the first extensive explorations of the tone cluster. During the same period, Charles Ives employed them in several compositions that were not publicly performed until the late 1920s or 1930s, as did Béla Bartók in the latter decade. Since the mid-20th century, they have prominently featured in the work of composers such as Lou Harrison, Giacinto Scelsi, Alfred Schnittke and Karlheinz Stockhausen, and later Eric Whitacre. Tone clusters also play a significant role in the work of free jazz musicians such as Cecil Taylor, Matthew Shipp, and Kevin Kastning.
In most Western music, tone clusters tend to be heard as dissonant. Clusters may be performed with almost any individual instrument on which three or more notes can be played simultaneously, as well as by most groups of instruments or voices. Keyboard instruments are particularly suited to the performance of tone clusters because it is relatively easy to play multiple notes in unison on them.
Music theory and classification
Prototypical tone clusters are chords of three or more adjacent notes on a chromatic scale, that is, three or more adjacent pitches each separated by only a semitone. Three-note stacks based on diatonic and pentatonic scales are also, strictly speaking, tone clusters. However, these stacks involve intervals between notes greater than the half-tone gaps of the chromatic kind. This can readily be seen on a keyboard, where the pitch of each key is separated from the next by one semitone : Diatonic scales—conventionally played on the white keys—contain only two semitone intervals; the rest are full tones. In Western musical traditions, pentatonic scales—conventionally played on the black keys—are built entirely from intervals larger than a semitone. Commentators thus tend to identify diatonic and pentatonic stacks as "tone clusters" only when they consist of four or more successive notes in the scale. In standard Western classical music practice, all tone clusters are classifiable as secundal chords—that is, they are constructed from minor seconds, major seconds, or, in the case of certain pentatonic clusters, augmented seconds. Stacks of adjacent microtonal pitches also constitute tone clusters.File:Thirteenth chord collapsed.png|thumb|A thirteenth chord collapsed into one octave results in a dissonant tone cluster|175x175px
In tone clusters, the notes are sounded fully and in unison, distinguishing them from ornamented figures involving acciaccaturas and the like. Their effect also tends to be different: where ornamentation is used to draw attention to the harmony or the relationship between harmony and melody, tone clusters are for the most part employed as independent sounds. While, by definition, the notes that form a cluster must sound at the same time, there is no requirement that they must all begin sounding at the same moment. For example, in R. Murray Schafer's choral Epitaph for Moonlight, a tone cluster is constructed by dividing each choir section into four parts. Each of the sixteen parts enters separately, humming a note one semitone lower than the note hummed by the previous part, until all sixteen are contributing to the cluster.
File:Harmonic series spacing successive octaves.png|thumb|By the fourth octave of the harmonic series, successive harmonics form increasingly small seconds the fifth octave of harmonics |350x350px
Tone clusters have generally been thought of as dissonant musical textures, and even defined as such. As noted by Alan Belkin, however, instrumental timbre can have a significant impact on their effect: "Clusters are quite aggressive on the organ, but soften enormously when played by strings." In his first published work on the topic, Henry Cowell observed that a tone cluster is "more pleasing" and "acceptable to the ear if its outer limits form a consonant interval." Cowell explains, "the natural spacing of so-called dissonances is as seconds, as in the overtone series, rather than sevenths and ninths....Groups spaced in seconds may be made to sound euphonious, particularly if played in conjunction with fundamental chord notes taken from lower in the same overtone series. Blends them together and explains them to the ear." Tone clusters have also been considered noise. As Mauricio Kagel says, "clusters have generally been used as a kind of anti-harmony, as a transition between sound and noise." Tone clusters thus also lend themselves to use in a percussive manner. Historically, they were sometimes discussed with a hint of disdain. One 1969 textbook defines the tone cluster as "an extra-harmonic clump of notes".
Notation and execution
In his 1917 piece The Tides of Manaunaun, Cowell introduced a new notation for tone clusters on the piano and other keyboard instruments. In this notation, only the top and bottom notes of a cluster, connected by a single line or a pair of lines, are represented. This developed into the solid-bar style seen in the image on the right. Here, the first chord—stretching two octaves from D2 to D4—is a diatonic cluster, indicated by the natural sign below the staff. The second is a pentatonic cluster, indicated by the flat sign; a sharp sign would be required if the notes showing the limit of the cluster were spelled as sharps. A chromatic cluster—black and white keys together—is shown in this method by a solid bar with no sign at all.In scoring the large, dense clusters of the solo organ work Volumina in the early 1960s, György Ligeti, using graphical notation, blocked in whole sections of the keyboard.
The performance of keyboard tone clusters is widely considered an "extended technique"—large clusters require unusual playing methods often involving the fist, the flat of the hand, or the forearm. Thelonious Monk and Karlheinz Stockhausen each performed clusters with their elbows; Stockhausen developed a method for playing cluster glissandi with special gloves. Don Pullen would play moving clusters by rolling the backs of his hands over the keyboard. Boards of various dimension are sometimes employed, as in the Concord Sonata of Charles Ives; they can be weighted down to execute clusters of long duration.
Several of Lou Harrison's scores call for the use of an "octave bar", crafted to facilitate high-speed keyboard cluster performance. Designed by Harrison with his partner William Colvig, the octave bar is
a flat wooden device approximately two inches high with a grip on top and sponge rubber on the bottom, with which the player strikes the keys. Its length spans an octave on a grand piano. The sponge rubber bottom is sculpted so that its ends are slightly lower than its center, making the outer tones of the octave sound with greater force than the intermediary pitches. The pianist can thus rush headlong through fearfully rapid passages, precisely spanning an octave at each blow.
Use in Western music
Before the 1900s
The earliest example of tone clusters in a Western music composition thus far identified is in the Allegro movement of Heinrich Biber's Battalia à 10 for string ensemble, which calls for several diatonic clusters. An orchestral diatonic cluster, containing all the notes of the harmonic minor scale, occurs also in the representation of chaos in the opening of Jean-Féry Rebel's 1737–38 ballet Les Élémens.File:Rebel, les Elemens, opening 02.png|thumb|center|500px|Rebel, Les Élemens,
From the next century-and-a-half, a few more examples have been identified, mostly no more than a fleeting instance of the form, for example in the opening of J.S. Bach's Cantata O Ewigkeit, du Donnerwort, BWV 60 or in the concluding two bars of the "Loure" from the same composer's French Suite No. 5, BWV 816:
or the collisions that result from the interaction of multiple lines "locked together in suspensions" in Bach's The Musical Offering:
In the keyboard sonatas of Domenico Scarlatti, we find a more daring and idiosyncratic use of tone clusters. In the following passage from the late 1740s, Scarlatti builds the dissonances over several bars:
Ralph Kirkpatrick says that these chords "are not clusters in the sense that they are arbitrary blobs of dissonance, nor are they necessarily haphazard fillings up of diatonic intervals or simultaneous soundings of neighboring tones; they are logical expressions of Scarlatti's harmonic language and organic manifestations of his tonal structure." Frederick Neumann describes Sonata K175 as "full of Scarlatti's famous tone clusters". During this era, as well, several French programmatic compositions for the harpsichord or piano represent cannon fire with clusters: works by François Dandrieu, Michel Corrette, Claude-Bénigne Balbastre, Pierre Antoine César, Bernard Viguerie, and Jacques-Marie Beauvarlet-Charpentier.
A dramatic use of a "virtual" tone cluster can be found in Franz Schubert's song "Erlkönig". Here, a terrified child calls out to his father when he sees an apparition of the sinister Erl King. The dissonant voicing of the dominant minor ninth chord used here is particularly effective in heightening the drama and sense of threat.
Writing about this passage, Richard Taruskin remarked on the "unprecedented... level of dissonance at the boy's outcries.... The voice has the ninth, pitched above, and the left hand has the seventh, pitched below. The result is a virtual 'tone cluster'... the harmonic logic of these progressions, within the rules of composition Schubert was taught, can certainly be demonstrated. That logic, however, is not what appeals so strongly to the listener's imagination; rather it is the calculated impression of wild abandon."
The concluding Arietta from Beethoven’s last Piano Sonata No. 32, Op. 111 features a passage which, according to Martin Cooper “gives a momentary touch of blurredness by the repeated cluster of fourths.”
The next known compositions after Charpentier's to feature tone clusters are by Charles-Valentin Alkan. One is Une fusée Op. 55, published in 1859, where the last page calls for a chord in the low register, pounded five times in a row, reading G–A–B–C–D–E–F–G, in which each of the three seconds on white keys are to be taken by a single finger. The other is "Les Diablotins", a miniature from the set of 49 Esquisses for solo piano, published in 1861.
There is also the solo piano piece Battle of Manassas, written in 1861 by "Blind Tom" Bethune and published in 1866. The score instructs the pianist to represent cannon fire at various points by striking "with the flat of the hand, as many notes as possible, and with as much force as possible, at the bass of the piano." This rolled G–A–B–C cluster later appears in Louis Moreau Gottschalk's Grande Fantaisie Triomphale sur L'hymne National Brésilien, published in 1869. The section features a stark contrast between the C major cluster against the key of F Major. In 1887, Giuseppe Verdi became the first notable composer in the Western tradition to write an unmistakable chromatic cluster: the storm music with which Otello opens includes an organ cluster that also has the longest notated duration of any scored musical texture known. The choral finale of Gustav Mahler's Symphony No. 2 features a tone cluster of great poignancy arising naturally out of voice leading to the words "wird, der dich rief, dir geben":
Still, it was not before the second decade of the twentieth century that tone clusters assumed a recognized place in Western classical music practice.