Orchestra

An orchestra is a large instrumental ensemble, most often associated with classical music or jazz, that brings together instruments from several families. Its four main sections are strings, woodwinds, brass, and percussion. The string section includes violins, violas, cellos, and double basses. Woodwinds typically consist of flutes, oboes, clarinets, and bassoons, with occasional additions like the piccolo, cor anglais, bass clarinet, contrabassoon, and saxophone. Brass instruments commonly include the French horn (often just called the horn), trumpet, trombone, and tuba, sometimes joined by the cornet and euphonium. Percussion covers timpani, snare drum, bass drum, cymbals, triangle, tambourine, tam-tam, and mallet percussion instruments. The harp appears fairly often in modern orchestras, especially for Romantic-era music. Keyboard instruments such as the piano, harpsichord, pipe organ, free-bass accordion, and celesta may form a fifth keyboard section or appear as soloists. For some contemporary works, electronic instruments and guitars are also included.

A full-size Western orchestra is sometimes called a symphony orchestra or a philharmonic orchestra—the latter term coming from Greek words meaning "loving" and "harmony." The number of musicians in a given performance can range from seventy to over one hundred, depending on the piece and the size of the venue. A chamber orchestra (sometimes called a concert orchestra) is a smaller group, usually no more than about fifty musicians. Orchestras specializing in Baroque music, such as that of Johann Sebastian Bach and George Frideric Handel, or Classical repertoire, like that of Haydn and Mozart, tend to be smaller than those performing Romantic works, such as the symphonies of Ludwig van Beethoven and Johannes Brahms. The typical orchestra grew in size throughout the 18th and 19th centuries, reaching a peak with the large ensembles of up to 120 players called for by Richard Wagner and later Gustav Mahler.

Orchestras are usually led by a conductor, who directs the performance using hand and arm movements, often made more visible with a short wooden rod called a baton. The conductor unifies the group, sets the tempo, and shapes the overall sound. Before a public concert, the conductor leads rehearsals, giving instructions on how the music should be interpreted. The principal player of the first violin section—known as the concertmaster (or "leader" in the UK)—also plays a key role in guiding the musicians. During the Baroque era (1600–1750), orchestras were often led by the concertmaster or by a musician playing the basso continuo parts on a harpsichord or pipe organ, a tradition that some 20th- and 21st-century early music ensembles continue.

Orchestras perform a wide range of repertoire, including symphonies, overtures for opera and ballet, concertos for solo instruments, and pit ensembles for operas, ballets, and some types of musical theatre, such as Gilbert and Sullivan operettas. Amateur orchestras include youth orchestras made up of students from elementary schools, high schools, or universities, as well as community orchestras, which typically consist of amateur musicians from a particular city or region. The word "orchestra" comes from the Greek ὀρχήστρα (orchestra), the name for the area in front of the stage in ancient Greek theatre where the chorus performed.

During the Baroque era, the size and makeup of an orchestra were not standardized, with large differences across European regions in terms of size, instrumentation, and playing styles. Baroque orchestras ranged from small ensembles with one player per part to larger groups with many players per part. For instance, Bach’s orchestra in Köthen had access to up to 18 players, while Corelli’s orchestra in Rome ranged from 35 to 80 players for regular performances and could be enlarged to 150 for special occasions. In the Classical era, the orchestra became more standardized, featuring a small to medium-sized string section and a core wind section of paired oboes, flutes, bassoons, and horns, sometimes supplemented by percussion and paired clarinets and trumpets.

The so-called "standard complement" of doubled winds and brass in the orchestra, which emerged in the late 18th century and solidified during the first half of the 19th, is generally credited to the forces Beethoven used after Haydn and Mozart. Beethoven’s instrumentation almost always included paired flutes, oboes, clarinets, bassoons, horns, and trumpets, with exceptions like his Symphony No. 4, Violin Concerto, and Piano Concerto No. 4, each of which specifies a single flute. Beethoven carefully expanded this timbral palette in his Symphonies 3, 5, 6, and 9 for innovative effect. The third horn in the "Eroica" Symphony provides harmonic flexibility and a "choral" brass effect in the Trio movement. Piccolo, contrabassoon, and trombones add to the triumphant finale of his Symphony No. 5. A piccolo and a pair of trombones help create the storm-and-sunshine effect in the Sixth, also known as the Pastoral Symphony. The Ninth calls for a second pair of horns, for reasons similar to the "Eroica"—four horns has since become standard—and Beethoven’s use of piccolo, contrabassoon, trombones, untuned percussion, chorus, and vocal soloists in its finale marks his earliest suggestion that the timbral boundaries of the symphony could be pushed further.