The Opera Orchestra is an integral part of the opera. It is much like a symphony orchestra. The orchestra is made up of four instrumental families—strings, woodwinds, brass and percussion—plus a group of miscellaneous instruments. The orchestra is led by the conductor, or maestro, who stands in the pit in front and below the stage. The conductor is fully responsible for the progress of the opera. He or she must blend and balance the music at all times, keep proper tempo and regulate the dynamics. The conductor also cues each singer when they are to begin singing. In some opera houses, video screens placed around the stage and auditorium transmit a live picture of the conductor in the pit. This keeps the singers from having to look down into the pit all the time.
While the orchestra may be used simply to accompany a singer or singers, it usually enhances the drama by being an independent and equal partner with the singers. Though it is not visible to many of the audience members, it is an extremely important contributor to the impact of the production.
Musical instruments have been around since prehistoric times, and there is hardly a civilization that did not have, at the very least, a drum or flute of some sort. Music has been used to accompany performances as long as they have existed. The first operas were usually accompanied by whatever instruments were available, and parts were not specifically written for the orchestra. Instead, the instruments doubled the voices, that is, they played the same melodies. The composer Monteverdi is often given the honor of having created the beginning of the orchestra as we know it. The musicians of the time were given an indication of chords to be played, called a figured bass, and they improvised from that. By the time of Bach and Handel in the 18th century, there were still no prescribed parts for the keyboard instruments. In the late 18th century, at the time of Mozart, most orchestras used a variety of instruments, and parts were especially written for them. Many of the instruments in a modern orchestra started in opera orchestras.
Opera Basics text courtesy of San Diego Opera and Elizabeth Otten.