Béla Bartók in the context of "A-flat clarinet"

Diatonic and chromatic are terms in music theory that are used to characterize scales. The terms are also applied to musical instruments, intervals, chords, notes, musical styles, and kinds of harmony. They are very often used as a pair, especially when applied to contrasting features of the common practice music of the period 1600–1900.

These terms may mean different things in different contexts. Very often, diatonic refers to musical elements derived from the modes and transpositions of the "white note scale" C–D–E–F–G–A–B. In some usages it includes all forms of heptatonic scale that are in common use in Western music (the major, and all forms of the minor).

The term string quartet is a type of musical composition or a group of four people who play them. Many composers from the mid-18th century onwards wrote string quartets. The associated musical ensemble consists of two violinists, a violist, and a cellist.

The string quartet was developed into its present form by the Austrian composer Joseph Haydn, whose works in the 1750s established the ensemble as a group of four more-or-less equal partners. Since that time, the string quartet has been considered a prestigious form; writing for four instruments with broadly similar characteristics both constrains and tests a composer. String quartet composition flourished in the Classical era, and Mozart, Beethoven and Schubert each wrote a number of them. Many Romantic and early-twentieth-century composers composed string quartets, including Mendelssohn, Schumann, Brahms, Dvořák, Janáček, and Debussy. There was a slight lull in string quartet composition later in the 19th century, but it received a resurgence in the 20th century, with the Second Viennese School, Bartók, Shostakovich, Babbitt, and Carter producing highly regarded examples of the genre, and it remains an important and refined musical form.

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 (such as C, C♯, and D) 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.

Hungary has made many contributions to the fields of folk, popular and classical music. Hungarian folk music is a prominent part of the national identity and continues to play a major part in Hungarian music. The Busójárás carnival in Mohács is a major folk music event in Hungary, formerly featuring the long-established and well-regarded Bogyiszló orchestra. Instruments traditionally used in Hungarian folk music include the citera, cimbalom, cobza, doromb, duda, kanászkürt, tárogató, tambura, tekero and ütőgardon. Traditional Hungarian music has been found to bear resemblances to the musical traditions of neighbouring Balkan countries and Central Asia.

Hungarian classical music has long been an "experiment, made from Hungarian antedecents and on Hungarian soil, to create a conscious [variant of] musical culture [using the] musical world of the folk song". Although the Hungarian upper class has long had cultural and political connections with the rest of Europe, leading to an influx of European musical ideas, the rural peasants maintained their own traditions such that by the end of the 19th century, Hungarian composers could draw on rural peasant music to (re)create a Hungarian classical style. For example, Béla Bartók and Zoltán Kodály, two of Hungary's most famous composers, are known for using folk themes in their music. Bartók collected folk songs from across Central and Eastern Europe, including Croatia, Czechia, Poland, Romania, Slovakia and Serbia, whilst Kodály was more interested in uncovering a distinctively Hungarian musical style.

Erwartung (Expectation), Op. 17, is a one-act monodrama in four scenes by Arnold Schoenberg to a libretto by Marie Pappenheim (de). Composed in 1909, it was not premiered until 6 June 1924 in Prague conducted by Alexander Zemlinsky with Marie Gutheil-Schoder as the soprano. The opera takes the unusual form of a monologue for solo soprano accompanied by a large orchestra. In performance, it lasts for about half an hour. It is sometimes paired with Béla Bartók's opera Bluebeard's Castle (1911), as the two works were roughly contemporary and share similar psychological themes. Schoenberg described Erwartung, saying "the aim is to represent in slow motion everything that occurs during a single second of maximum spiritual excitement, stretching it out to half an hour."

Philip Friedheim has described Erwartung as Schoenberg's "only lengthy work in an athematic style", where no musical material returns once stated over the course of 426 measures. In his analysis of the structure, one indication of the complexity of the music is that the first scene of over 30 bars contains 9 meter changes and 16 tempo changes. Herbert Buchanan has countered this description of the work as "athematic", and the general impression of it as "atonal", in his own analysis.

Music for Strings, Percussion and Celesta, Sz. 106, BB 114 is one of the best-known compositions by the Hungarian composer Béla Bartók. Commissioned by Paul Sacher to celebrate the tenth anniversary of the chamber orchestra Basler Kammerorchester, the score is dated 7 September 1936.

The work was premiered in Basel, Switzerland, on January 21, 1937 by the chamber orchestra conducted by Sacher, and was published the same year by Universal Edition.