orchestra (Fr. orchestre, Ger. Orchester). A mixed body of instrumentalists for the perf. of symphonic and other works. There are various types of orch., e.g. symphony orchestra, a body of (usually) over 90 players able to play elaborate works; chamber orchestra, small version of above (from, say, 15 to 45 players); string orchestra, strings only; theatre orchestra, medium-size orch. used for musicals, etc., and often incl. saxs.

The orch. has changed and developed over the centuries, the standard version today comprising str., woodwind, brass, and perc. In the 17th cent. the orch. was a haphazard affair, often incl. viols, fls., obs., cornetts, tbs., drums, and hpd. In the 18th cent., with instr. improvements, vns. ousted viols. Accs. were realized by the harpsichordist or org. from a figured bass. From c.1800, the orch. became more elaborate and composers more skilled in its use, obtaining tone-colour by subtle combinations and by solo passages. In Beethoven's 1st Sym. (1800) the orch. consisted of: vns., div. into 1st and 2nd sections, vas., vcs., dbs., fls., obs., cls., bns., tpts., hns., timp. Later composers added the harp and Berlioz enlarged the woodwind, brass, and perc. departments, as did Wagner and Liszt. Towards the end of the 19th and in the 20th cents., composers enlarged the orch. enormously, and we have the marvellously rich, exotic, and grandiose orch. works of Strauss, Mahler, Elgar, Havergal Brian, Ravel, Stravinsky, and many more. Huge brass sections are often a feature of their scores, with triple or quadruple woodwind (i.e. 3 or 4 of each instr.). Later in the 20th cent. even more variety in orch. use is encountered, with reversions to small combinations of instr., works scored for solo instr. and wind or brass instr. only, exotic perc. effects, and of course the addition of elec. instr., tape-recorded and synthesized effects.

The lay-out of the standard sym. orch. is normally as shown in the diagram opposite, but certain works call for special seating arrangements and some conds. have individual preferences.