Baroque orchestras generally used a four-part string section. The flute replaced the recorder, purely because of the greater penetration of the flute sound. Oboes and bassoons were standard, and a pair of horns also became normal. However, much depended upon the instruments and players that were available at the time, so Bach's orchestras tended to have a variable line-up. For example, the six cantatas that make up the Christmas Oratorio of 1734 call for an unusual orchestra, comprising:
2 Oboes d'amore (an early oboe with a slightly lower range)
2 Oboes da caccia (another early oboe, shaped like a hunting horn)
2 Corni da caccia (hunting horns)
Continuo (bassoon, cellos, string bass, and organ)
(There are some short clips of instruments from Bach's time at Bachdigital).
Handel worked with similar constraints, including additional or unusual instruments where a player was available. Thus the harp was included in Esther, and trombones in Saul and Israel in Egypt. Vivaldi also wrote many (about 550!) concertos for orchestral instruments, including unusual ones such as viola d'amore, mandolins and the newly emerging clarinet. These pieces drew upon the skills of the musicians at the Ospedale della Pietà in Venice.
The consistent feature of all these orchestras was the string section, enhanced now by double basses and a large violin section (the viola was still present, but no longer the most common string instrument). This was the period of the great violin makers, and the sound of the violin came to dominate music-making. Woodwind instruments varied greatly in both quality and usefulness. The oboe da caccia was gradually replaced by the English horn. Bass oboes were made, but fairly quickly abandoned. There were double-bassoons and, later in the 18th century, tenor clarinets or basset-horns.
The other consistent sound in the baroque orchestra was the continuo. This was usually played on a keyboard instrument such as harpsichord or organ, or on a plucked string such as lutes and theorbos, or sometimes harp. The continuo part was improvised to a figured bass and would hold the music together. The director of an orchestral performance at this time would be either the first violin or sometimes (as, for example, when a well-known composer was performing) the keyboard player.
The essence of Baroque orchestral music was polyphonic counterpoint, i.e. music composed in lines, horizontally. The addition of figured bass began a move towards a more verticalised approach to composition which was bass driven and homophonic. The next major development in the orchestra derived from this change in style. In his his Dictionnaire de Musique (1754), Jean-Jacques Rousseau wrote:
"The greatest orchestra in Europe, as far as the number and intelligence of its performers is concerned, is that of Naples; but that which is the best distributed and forms the most nearly perfect ensemble is the orchestra of the opera of the King of Poland at Dresden directed by the famous Hasse."
The orchestra to which he referred was housed at the Dresden Hofkappelle, and its seating plan (enlarge the image to the right) shows a large string ensemble with both woodwind and brass instruments:
1. Harpsichord of the maestro di capella.
2. Harpsichord of the accompanist ( of the recitative )
5. First violins.
6. Second violins, with backs to theatre [the stage]
7. Oboes, the same.
8. Flutes, the same.
a. Violas, the same.
c. Hunting Horns
d. A platform at each side, for the timpani and trumpets.
With a few changes, this Baroque lineup was soon to evolve into the basis of the Classical orchestra.