<P> The leader of the first violin section, commonly called the concertmaster, also plays an important role in leading the musicians . In the Baroque music era (1600--1750), orchestras were often led by the concertmaster or by a chord - playing musician performing the basso continuo parts on a harpsichord or pipe organ, a tradition that some 20th century and 21st century early music ensembles continue . Orchestras play a wide range of repertoire, including symphonies, opera and ballet overtures, concertos for solo instruments, and as pit ensembles for operas, ballets and some types of musical theater (e.g., Gilbert and Sullivan operettas). </P> <P> Amateur orchestras include those made up of students from an elementary school or a high school, youth orchestras, and community orchestras; the latter two typically being made up of amateur musicians from a particular city or region . </P> <P> The typical symphony orchestra consists of four groups of related musical instruments called the woodwinds, brass, percussion, and strings (violin, viola, cello and double bass). Other instruments such as the piano and celesta may sometimes be grouped into a fifth section such as a keyboard section or may stand alone, as may the concert harp and electric and electronic instruments . The orchestra, depending on the size, contains almost all of the standard instruments in each group . </P> <P> In the history of the orchestra, its instrumentation has been expanded over time, often agreed to have been standardized by the classical period and Ludwig van Beethoven's influence on the classical model . In the 20th century, new repertory demands expanded the instrumentation of the orchestra, resulting in a flexible use of the classical - model instruments and newly developed electric and electronic instruments in various combinations . </P>

The orchestra has how many primary instrument groups