Evolution of the Orchestra in the Classical Period
In Baroque music, strings were the most important parts. The late Baroque orchestra as we know in the works of Handel and Bach originated in France. It was Lully's reforms that divided the strings into four or five sections. This idea persisted during the Classical and Romantic periods. In the Baroque orchestra, the strings and winds played the same sort of music melodically and rhythmically. The woodwind and brass were used as melodic instruments but later (when the continuo was discontinued) they were mainly used to sustain the harmony. Instrumental idioms were frequently interchangeable (transference of idioms). In the earlier part of the 18th century, Rameau introduced interesting and unexpected passages on the flutes, oboes, and bassoons and thus opened the path to the colouristic treatment of the orchestra [he is also the first to use the clarinet in his opera Zoroastre in 1749]. Gluck was the pioneer for the solid and massive style orchestration. The orchestra gained importance with the transformation of operatic prelude to the symphony towards the middle of the century. In the middle of the century small groups of players -mostly strings- were still frequent. Before long, two oboes and two horns were added, and then gradually bassoons, flutes, trumpets, timpani and two additional horns. The core of the symphony orchestra, the strings, evolved into the string quartet. Somewhat later, clarinets were incorporated into the orchestra, and for special effects trombones, double-bassoon, piccolo flute, English horn, basset horn and the 'Janissary' instruments, like triangle, cymbals, and large drum.
The usual symphonic orchestration at the middle of the eighteenth century gave all the essential musical material to the strings, and used the winds only for doubling, reinforcing, and filling in the harmonies. The style of orchestral music in the 1750s and 1760s was still dependent on the idea of the continuo [the disappearance of the basso continuo began about 1760, by the end of the century it was obsolete]. A clear polarity between the top line and the bass lingered on into the Classical style, and dialogue involving inner parts was rare. The continuity of texture was emphasized by holding notes in the woodwind and horns, and writing for strings explored a variety of accompanimental textures which provided a stable background for changing melody instruments on the top line.
Later in the century, the wind instruments were entrusted with more important and more independent material. J Stamitz developed the dramatic resources of the orchestra, especially the strings section, by the use of dynamic varieties. CPE Bach's four symphonies (written about 1776) represent the final phase of orchestration prior to the masterworks of Viennese Classicists. They are scored for pairs of flutes, oboes, horns, one or two bassoons and the usual group of strings. The strings give melodic activity and figuration while the winds provide harmony and body. During the period of Haydn and Mozart, the number of strings grew larger in proportion to the number of performers in the orchestra. Each wind instrument was regarded equal to the strings in terms of playing the melody as well as aiding in the supplying of the harmony. Instruments are no longer omitted from the entire movements except in the trio of the minuet. The instrumental group was standardized in the late symphonic works of Haydn and Mozart and in the majority of those by Beethoven: double woodwind (pairs of flutes, oboes, clarinets, bassoons), pairs of horns, trumpets, timpani and the standard strings (first violins, second violins, violas, cellos, and double basses). In the Classic orchestra, winds and strings were self-contained, melodically and harmonically independent of one another.
In the classical era, the strings gained variety and freedom for effects such as changing rhythmic patterns, pizzicato, tremolo and double stopping. Basso continuo was discarded. With the final disappearance of the harpsichord from the symphony orchestra towards the end of the eighteenth century, the leader of the violins took up the responsibility to conduct the group. In general, the strings are the backbone of the orchestra and given the most important melodic parts of the score. Next in importance as melody instruments are woodwinds (flute, clarinet, oboe) each of which has a very characteristic timbre or tone-colour. However, if they continue too long, they tire the listener's ears. Therefore, they are used sparingly as colour effects. With the emphasis in music shifting towards melody, the woodwind section was created in the orchestra in the eighteenth century. The four main woodwind instruments (flute, oboe, clarinet, bassoon) are so well contrasted in colour.
Late in the eighteenth century, the flute parts began to occupy a position in the orchestra on an equal footing with the oboe. It was used more as a solo instrument rather than only in tutti parts. Flute parts tended to lie higher. When doubling oboe parts, they did so at the octave above. Embellishments started. (Flute was an extra part in Baroque ensembles; it was oboes and bassoons only). Only one pair of woodwind instruments should play in the soprano register seems to have been a firmly established idea in the earlier part of the century. As a general rule, when flutes appeared in the score, the oboes temporarily retired (partly due to the fact that they were played by the same person).
Oboe and bassoon parts were less florid than in Baroque music and helped sustain the harmony together with the horns. Used together mainly as harmony instruments. No longer so active as flutes. However, they were prominent as 'solo' instruments in a way that was less common in Baroque music.
Clarinet became popular from the second half of the 18th century and established a place in the orchestra. Its potential as a solo instrument was recognised in opera, symphony, concerto and oratorio. When the clarinet first began to occupy a place in the score, it was not so much side by side with the oboes as in place of them. Clarinets step into the place vacated for the time being by the oboes. It is interesting to note that when Mozart added the clarinet part to Symphony No. 40 (K550), he rewrote the oboe parts so that they never play together except in tuttis. Clarinets were found to be better partners for horns than oboes. Mozart was the first to exploit the rich lower register of the clarinet.
Horns were used to blend in, to add colour, cohesion and volume. They frequently emphasise strong rhythms and reinforce the tutti, particularly at cadences and in martial music. Horn parts usually fill out the inner harmonic structure and are less concerned with melodic outlines. In the 1760s and 1770s, the horns played in the first and last movements, and later began to find their way into the minuet and slow movements. After 1780, horn parts were lower in pitch, became simpler and lost their conjunct/stepwise melodic characteristics of Baroque parts (before 1780, Haydn and Mozart wrote high and difficult horn parts).
Horn and trumpet parts are usually indistinguishable and almost interchangeable. Horns are associated with hunting field and trumpet with battle field. Trumpet parts became lower and more manageable. Trumpets and drum were used for rhythmic patterns, marking accents and underlying rhythms, adding excitement, and to emphasise climaxes. The limitations of natural (valveless) trumpet and horn were similar. The traditional melodic field for the natural horn and trumpet was the fourth to the twelfth harmonics.
Trombones were regularly used in church music and opera (mainly for solemn and tragic effects not only to increase the volume), but not found in symphonic music until the time of Beethoven (5th Symphony). At the time of Wagner, they became a usual member of the orchestra.