The pipe organ is a wind instrument played from a console with one or more keyboards. Though by no means standard, the modern church organ console usually consists of two manual keyboards and a pedalboard for the feet. The organ, unlike the piano, gives the player the opportunity to change the timbre of the sound through the use and combination of various different ranks of pipes.
Due to its association with religious service and a lack of a presence on the public stage, the organ's popularity as a field of study and as a performance instrument has declined sharply since the second World War. Some popular songs in the post-WWII era make use of electronic organs - essentially synthesizers - but the organ's use in the popular mind has been relegated to the church.
The pipe organ in Western Europe first came into existence in the latter half of the first millennium. The early organ was only capable of producing a single note at a time to accompany the singing of chant, and had to be pumped by the player in order to generate sound. Interestingly, the early organs, based on information from tapestries of the time, had a different scale (ratio of width to length) for each pipe, resulting in a different timbre for each note; ranks of pipes on more modern instruments all have the same scale, and thus generate a unified sound. Rather than keys, these proto-organs had drawn sliders which the player pulled out to create sound, aligning holes in the sliders with the base of the pipe and allowing wind to pass through from the bellows.
The keyboard was the first major and universal modification made to the instrument. The keyboard was both easier to operate and somewhat more versatile than sliders, allowing for greater dexterity from the player and the sounding of more than one note at a time. Early keyboards began appearing sometime around the twelfth century. Also at roughly this time, the pipework became more complex, involving several ranks of pipes in the instrument. Each note would sound all the pipes in its rank (a "Blockwerk"). Organ builders then started putting multiple instruments together to give the organist a way to vary dynamics or sound. With more for the organist to do, or simply requiring more air than a single person could produce, several organs had bellows meant for someone (or several people) other than the organist to operate.
The next great invention followed on the heels of the keyboard: the "stop," the means by which certain ranks of pipes could be used and others left inactive. In its simplest form, the stop is a slider with holes in it; when in the "off" position, those holes do not line up with the pipes, which doesn't allow air through.
The pedalboard, the most obvious distinction between the organ and other keyboard instruments appeared next. In their original incarnation, the pedals didn't activate a separate organ, as distinct manuals did; instead, they duplicated the effect of the lowest range of one of the manuals. This was referred to as a "pull-down" system, as playing the pedal pulled down the notes of the manual keyboard. Later, pedalboards incorporated their own stops.
As the organ's mechanism became more complex in the nineteenth century, more new devices were added to the instrument. Common modifications include:
- divisions of pipes that were "enclosed" in a separate box, with shutters (operated by the organist) to change the volume level and timbre of the stops;
- mechanical means of changing the active stops at the touch of a button or lever;
- a device for gradually adding or removing stops in a prescribed order
The organ remained essentially unchanged until the advent of steam power and, later, the harnessing of electricity, which allowed fully mechanical actions to be replaced with other means. This also meant that the organist didn't need to employ people to work the bellows. Still more recently, wholly electronic organs have been created, some of which are capable of rivalling pipe organs.
Organ music differs substantially from that of other keyboard instruments for a few reasons. First, until the advent of enclosed divisions and the register crescendo, the organ had no way of changing volume in a graduated manner, an advantage which the pianoforte holds over all other keyboard instruments. Secondly, the organ, due to the nature of its sound-producing mechanism, can sustain a tone indefinitely, a fact of which many composers of organ music made (and continue to make) great use. Third, the organ doesn't take well to rapid flourishes of many notes, requiring a certain amount of time to sound properly. Fourth, because of the nature of the sound, organs are more suited to linear and contrapuntal textures than more homophonic or monodic ideas. As a result, organ music tends to be more grandiose, more drawn out, and more contrapuntal than piano music, with less overt virtuosity.
The standard repertoire for organists also extends to greater reaches of history and to more generally unknown composers than most other instruments. Standard concert music for the organ reaches back into the sixteenth century, and focusses strongly on many lesser-known composers of the late nineteenth century. While many composers of organ music wrote for other instruments as well, they tend to be most strongly identified with the organ - Johann Sebastian Bach being the most notable exception.