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Stop (Pipe Organ)On a pipe organ, a stop is: - A set of pipes tuned to a scale (with one or more pipes per note).
- The control that connects that set of pipes to a keyboard, either pedal or manual.
A rank is a set of pipes tuned to a scale, with one pipe per note. Thus a stop may consist of one or more ranks. A stop consisting of more than one rank is termed a mixture, and the number of ranks is commonly indicated by a roman numeral following the stop name, for example a Cornopean IV is a mixture consisting of four ranks of reed pipes. Pitch A stop may be tuned to sound (or speak at) the pitch normally associated with the key that is pressed (the written pitch), or it may be pitched at a fixed interval above or below this pitch. A stop pitched at the written pitch is known as an 8' stop, pronounced eight foot. A stop an octave above is termed 4', an octave below is 16', and so on, the footage being the approximate length of an open flute pipe sounding a C two octaves below middle C at that pitch. Thus, the pitches which sound the octaves above and below written pitch (and therefore have the same note name) are the powers of two: 1' is three octaves above, 2' two octaves above, 4' one octave above, 8' written pitch or unison, 16' one octave below, 32' two octaves below, and 64' three octaves below. Pitches which are not powers of two are at some other interval, and are called mutation stops. There is no standard naming of these, for example 3' and 2 2/3' are both used to describe a stop sounding an interval of a twelfth above written pitch. Flue stops, reed stops, and others Nearly all stops (there are however notable exceptions) fall into one of two types: - Flue stops. The pipes of a flue stop are actuated by a whistle or fipple. Most of the pipes of a pipe organ are flue pipes. Diapason (see below) stops are nearly always single ranks of flue pipes, as are most single rank mutation stops.
- Reed stops. The pipes of a reed stop are actuated by a beating reed. Reed pipes are used both for single rank stops, and for mixtures. Most but not all mixtures are of reed pipes.
Flue pipes are further divided in several ways. Open and stopped pipes A stopped pipe sounds an octave below an open pipe of the same length, as well as a giving a different sound. Stopped pipes are also known as gedacht or gedakt, after the german word for covered. Thus a closed pipe is physically half the length of an open pipe sounding the same note, making the larger pipes in particular cheaper to make and easier to fit into an organ case. So while the main reason for choosing to make a pipe open or closed is the sound, cost and practicality may also enter into the decision, particularly for 16' and deeper stops to be used with the pedals. Flutes, strings and others Most (not all) flue pipes are of one of three tone families: - Flutes have the purest waveforms.
- Diapasons or principals have the strongest sounds, and are midway between flutes and strings in tone.
- Strings have the richest harmonics, and the pipes of these stops tend to be narrower to produce this effect.
Ranks of all three tone families may be either stopped or open, and made either of metal or of wood. Metal pipes are normally round in cross section, while wooden pipes are most often square. Originally this was for ease of manufacture, more recently it is also for reasons of tradition. Unfortunately, the above terms are far from standardised. Some builders, for example, use the term flute to mean a stopped flute or diapason, and/or the term diapason to mean an open diapason. The most common flue stop not of any of these families is the rhorflot, see below. Naming of stops Many stops have more than one name. The choice of the name reflects not only the tone of the stop, but also the style of the particular organ, for example a baroque organ will generally have its stop names derived from the german, while an english romantic organ will have the names of similar stops derived from the traditions of its style. Some common stops include: - Celeste: A flue stop tuned slightly sharp to create a beat effect, intended to be used only with another flue stop of similar tone. Most commonly at 8' or 4'.
- Cremona: A reed mixture. The name has nothing to do with the town of Cremona in Italy or the famous school of violin makers who lived there, but is a corruption of the german krumhorn.
- Diapason: A flue stop intended to be the backbone of the sound, and traditionally and most commonly at 8' on a manual, and 8' or 16' on the pedals. It may be open or stopped. Some modern makers use the term Principal instead.
- Fifteenth: A 2' diapason.
- Flute: A single rank of open or stopped flue pipes with a relatively pure sound, weak in overtones. In some organ styles, synonymous with stopped diapason. One of the most common ranks to break in the lower octaves, for example an open flute of metal may have the lowest octave of pipes stopped and made of wood, for reasons of space and economy.
- Mixture: While any multi-rank stop can be called a mixture, when a stop control is explicitly labelled Mixture, for example 8' Mixture III, it indicates a multi-rank stop intended to be used in chorus with other stops to build a full sound, rather than on its own. Most commonly composed of reed pipes, Mixture stops vary tremendously in tone, as they are designed to enhance whatever main stops are available.
- Oboe: A single-rank reed stop, often used as a solo stop and in swell and choir divisions.
- Octave, oktav (and other variant spellings): A 4' principale.
- Principale, principal, prinzipal: Unfortunately has two different meanings:
- Traditionally, a flue stop at 4'; The name is short for principal octave.
- More recently, a strongly voiced diapason, normally at 8'.
- Rhorflot: A semi-stopped flue pipe of metal, with a narrower, open-ended tube extending from the top of the pipe proper. This extension is confusingly known as a reed, which explains the name, from the german for reed flute.
- Two and twentieth: A 1' diapason, often the only 1' rank in an organ.
External links Borrowing and extension When a rank of pipes is available as part of more than one stop, this is called borrowing. Foe example, an 8' diapason rank may also be made available as a 4' octave. When both of these stops are selected and a key is pressed, say middle C, two pipes in the same rank will sound, the middle C pipe and the pipe one octave above it. However, if both middle C and the key an octave above it are pressed at once, only three pipes will sound, as one has been selected twice, once as the octave of middle C and once as the diapason of the key an octave above it. This is known as a borrowing collision, and is one reason that borrowing a rank is regarded as inferior to having a dedicated rank. The other is that a dedicated 4' stop would be designed and voiced slightly differently; There is of course no opportunity to do this with a borrowed rank. Ranks can be borrowed within a single manual or division of an organ, or between manuals. When a rank is borrowed, it may not exactly fit the keyboard. In the example above of an 8' diapason borrowed as a 4' octave, there are no pipes in the original rank to sound the top octave of the keyboard at 4'. The neatest and most common solution to this is to provide an extra octave of pipes used only for the 4' stop. The full rank of pipes is now an octave longer than the keyboard, and is called an extended rank or an extension rank. An organ that relies heavily on extension is called an extension organ. On heavily extended organs, some diapason ranks are commonly extended two octaves below and three octaves above 8', string ranks one octave below and one above, and flute ranks two or three octaves above. Extension is less commonly used for reed stops, one octave above to extend an 8' rank to 4' being the normal maximum, and very rarely for 64' stops, as large organs which have such large pipes tend to avoid borrowing altogether. Couplers A stop which connects two keyboards together is called a coupler. For example, a swell to great coupler connects the swell organ manual to the great so that whenever a key on the great organ is pressed, the corresponding key on the swell organ is also activated. On a mechanical action organ, the actual key on the coupled keyboard will be depressed. An electric or other indirect action organ may have mechanical couplers, which produce the same effect, or electrical couplers, which actuate the pipes without moving the relevant key. Equally common are octave couplers and suboctave couplers, which connect the keyboard being played to the octave or suboctave of the keyboard being coupled to it, respectively. There is never any attempt to extend the pipes of another keyboard to accomodate these couplers.
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