The typical symphony orchestra consists of four proportionate groups of similar musical instruments called the woodwinds, brass, percussion, and strings. 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. In the history of the orchestra, its instrumentation has been expanded over time, often agreed to have been standardized by the classical period and Beethoven's influence on the classical model.
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