The majestic pipe organ was one of largest, most complex machines in existence with hundreds of metal and wooden pipes arranged in dozens of ranks. It was played from several keyboards and a pedalboard. It achieved a level of tonal beauty, construction, and appearance hardly equaled today.
Organs were built to support worship and, with other instruments, to participate in the chief music of the service, the cantata. Many other instruments, especially strings, were developed to new levels of perfection.
In many regards, the 18th Century organs were marvelous instruments. Christoph Wolff states: "We must keep in mind that the organ represented one of the most complicated - and in the case of the Dutch and north German instrument types, also the largest - 'machines' in existence from the 16th through the centuries. The sound-producing miracle behind an ornamental and symmetrical facade of glistening metal pipes embodied the science of mechanical engineering, physics (acoustics), chemistry (metallurgy), and mathematics as well as architecture and the handicraft of carpentry and plumbing. It comprised a myriad of individual parts using all sorts of metal, wood, leather, ivory, cloth, and other materials. Its combination of wind chests, bellows, ranks of pipes, and keyboards was capable of producing colorful sonorities of different dynamic ranges, whose spectrum and volume depended on the size of the instrument." [Wolff, Johann Sebastian Bach, the Learned Musician, p.142].
A typical large late Baroque organ had as many as four keyboards and a pedalboard operating as many as five divisions of pipes at very low wind pressure. The keys activated the pipes by means of mechanical rods or trackers. Wind was supplied with human power by means of bellows. Pipe length ranged from less than one inch to 32 feet. Families of pipes included principals, flutes, and reeds and were capped by multiple pitch stops called mixtures.
Pipe tone was incisive, yet gentle, virile, or pungent. It was capable of blending in ensembles, yet often had solo potential. Organs were custom designed for each installation in a resonant room that served to enhance and project the tone.
The organs that Bach played are representative of instruments in north Germany. They reflected the economic prosperity of the region and the desire of church, civic, and commercial interests to erect utilitarian, artistic, and impressive monuments of appropriate size and great beauty. The Leipzig organ at St. Paul's was Bach's favorite. It was the one he was engaged to officially inspect when it was built, and the instrument he apparently chose for his own performances in Leipzig.
The organs were built to support the practice of music in worship. Builders
worked in conjunction with organists and designed instruments where the
developing repertoire of the organists, who usually were composers and
improvisers, could be played.