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An organ stop is a component of a pipe organ that admits pressurized air (known as wind) to a set of . Its name comes from the fact that stops can be used selectively by the organist; each can be "on" (admitting the passage of air to certain pipes), or "off" ( stopping the passage of air to certain pipes).
The term can also refer to the control that operates this mechanism, commonly called a stop tab, stop knob, or drawknob. On electric or electronic organs that imitate a pipe organ, the same terms are often used, with the exception of the Hammond organ and , which use the term "drawbar".
The term is also sometimes used as a synonym for register, referring to rank(s) of pipes controlled by a single stop. Registration is the art of combining stops to produce a certain sound. The phrase , which once only meant to engage all of the voices on the organ, has entered general usage, for deploying all available means to pursue a goal.
The mechanism for operating the stops varies widely, but the principle is the same: the stop control at the console allows the organist to select which ranks of pipes will sound when a key is pressed. When the organist desires a rank to sound, they operate the corresponding control at the console, allowing wind to flow to the pipes. Likewise, the organist can deny wind to the pipes by operating the same control in the opposite direction. Common stop controls include stop knobs, which move in and out of the console, and stop tabs, which toggle back and forth in position.
Some organs, particularly smaller historical organs from England, Spain or Portugal,Dalton, James. "Iberian organ music before 1700," in The Cambridge Companion to the Organ, ed. Nicholas Thistlethwaite and Geoffrey Webber (Cambridge University Press, 1998), p. 165. feature divided registers, in which there are two stop knobs for certain ranks. One stop knob will control the upper portion of the keyboard, and the other will control the lower portion of the keyboard. This arrangement allows the upper portion of the keyboard to sound a different registration than the lower portion, which lends a greater versatility to smaller organs, especially those with only one manual.
Ranks which are neither divided nor extended (see below Unification, borrowing and extension) generally contain as many pipes as there are keys on the keyboard to which they are assigned: in most cases 61 pipes for a rank assigned to a manual and 32 pipes for a rank assigned to the pedal.
Other common designs include the spring chest, the cone valve chest, and the Pitman chest.
Borrowing or duplexing refers to one rank being made available from multiple stop knobs, often on different manuals or pedal.Shannon, John R. Understanding the Pipe Organ, 2009, p. 83. Extension refers to the addition of extra pipes to the high and/or low ends of a rank in order to allow that rank to be borrowed by higher and/or lower stops. Unification and borrowing (duplexing) is mostly related to pipe organs with physical pipes; however, some (older) electronic organs also used unification and duplexing to expand the tonal resources of a limited number of synthesized virtual ranks.
While unification and extension increase the tonal resources and flexibility of the organ, greater care needs to be taken by the organist in registering the organ, particularly when the composition requires many notes to sound at the same time. In a non-unified organ, voices are scaled for their intended job. As an example, the octave (4′) diapason is generally of a smaller scale and softer than the corresponding 8′ diapason rank, whereas in unification they would be of the same strength due to using the same set of pipes. Straight reed choruses (16′, 8′ and 4′) have the luxury of ranks with different timbres, whereas a unified reed chorus has voices that are identical.
Playing with all stops out on a heavily unified/duplexed organ may result in chords that sound thinner or emphasize higher harmonics on some notes more than others, due to notes in different octaves using the same pipes instead of having their own. Part of an organist's training is to detect unification and duplexing and to create registrations that take them into account.Shannon, John R. Understanding the Pipe Organ, 2009, Chapter 6. Nonetheless, heavy unification can create issues for visiting artists with limited practice times, or those improvising compositions.
Borrowing between manuals occurs in English organs from about 1700, but extension of pipe ranks for the purpose of borrowing at different pitches is a relatively recent development. Extension and unification are heavily used in to produce the maximum number of voices from a minimal number of pipes. It is still typical to see a significant amount of unification and duplexing in practice organs and small church organs. Traditionally, less use has been made of extension in large church organs and those designed for classical music, with authorities tending to regard borrowing in general and extension in particular as things to be avoided if possible, except in a few cases where space for pipes is limited, making extension and/or unification necessary. Borrowing 16′ manual ranks for the pedal division is more widely employed because of the expense and space requirements of 16′ stops and the versatility this allows.
The pitch of a rank of pipes is denoted by a number on the stop knob. A stop which speaks at unison pitch, or "native pitch", is known as an 8′ (pronounced "eight-foot") stop. This nomenclature refers to the approximate length of the longest pipe in a rank of Open tube. In a rank of Closed tube, the lowest pipe is about 4 feet long, but because it sounds at unison pitch, it is also known as an 8′ stop.
Example:
The sounding length of a mutation stop gives the answer as to what pitch the rank sounds. For example, a stop labeled ′ (or one-third of 8′) has three times the frequency; i.e., the interval of a twelfth above unison pitch. This third harmonic (G) (twelfth, quint, qvinta, rorkvint, or nazard nasard) is the most-common pitch, followed by the fifth harmonic (E) (tierce terz) (′) and sixth (G) (larigot, nasat) (′), with rarer examples from higher in the series, such as the " septième" or " septima" (′) and " none" (′). There's also an ′ Major 7th which when C is played sounds a B below the top C of a piano.
Mutations usually sound at pitches in the harmonic series of the fundamental, and except when derived from unified ranks, are always tuned just intonation. Some organs contain mutations that are overtones of 16′ or 32′ to create combination tone, e.g., quint-bass ′. Such "helper ranks" that sound at the fifth just above or fourth below the fundamental (e.g., Bourdon 16′), can create the impression of a stop an octave lower than the fundamental (e.g., Bourdon 32′), saving the space and money otherwise needed for larger bass pipes; such an effect is termed a resultant.
This is a list of some mutation stops.
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!Harmonic
!Interval
!Length of pipe !Sounding note when C4 is played !Name on manual | ||||
| ()3rd harmonic of the note one octave below the fundamental | P5 | ′ | G4 | Quint |
| ()5th harmonic of the note one octave below the fundamental | M10 | ′ | E5 | Gross Tierce |
| 3 | P12 | ′ | G5 | Nazard, Twelfth |
| 5 | M17 | ′ | E6 | Tierce, Terz |
| 6 | P19 | ′ | G6 | Larigot |
| 7 | m21 | ′ | B♭6 | Septième |
| 9 | M23 | ′ | D7 | None |
| 13 | M27 | ′ | A7 | Tredezime |
| 19 | m31 | ′ | E♭8 | Mollterz |
| 48 | P40 | ′ | G9 | Quadragesima |
Mixtures have numbers that correspond to the pitch they make. For example, a mixture configured as: 12.15.19.22 contains, at its lowest note, the following ranks: ′, 2′, ′, 1′.
Mixtures usually have 'breaks' to prevent the inconvenience to the builder of making very small pipes at the top of the compass. A common configuration for the breaks is that for every octave the mixture lowers by a fifth.
The most common configuration of ranks for an 8′ fundamental is as follows: II = 12.17; III = 12.15.17; IV = 8.12.15.17; V = 1.8.12.15.17.
Cornet stops do not usually play the full compass; they generally play from either Middle C, or Tenor C, to the top. In British and French organs before the Victorian period, this allowed the Cornet stop to be raised up within the case relative to the other pipes of the Great organ around it for better projection; this is known as a 'Mounted Cornet' in English and 'Cornet Séparée' in French. Though used throughout Europe, the Cornet is especially associated with French organ builders, who used Cornets with particular regularity especially through the Eighteenth and Nineteenth centuries, since French chorus reed stops (Trompette, Bombarde, Clairon) are very strong in the bass (having un-weighted tongues) but, when on low wind pressures, comparatively weak further up the compass; the Cornet was therefore used to strengthen the treble ranges of these chorus reed stops. A characteristic example of this use is the classic French registration known as the 'Grand Jeu': a combination of Trompettes, Clairons and Cornets, together with the Prestant (by contrast the 'Plein Jeu' does not include cornets).
In French organs, when an 8 ft Bourdon was used with 4′ and 2′ stops plus a Nasard and Tierce the resulting ensemble was known as a 'Cornet Décomposée' (often confused with the 'Cornet Séparée' described above) since it had the same composition as a standalone Cornet stop.
Occasionally Cornets are supplied based on a 16′ fundamental (16′, 8′, ′, 4′ and ′), though the individual ranks are more usually configured as separate stops (for example the Grande Tierce ′ and Grand Nasard ′ supplied by the Isnard brothers at St Maximin, Provence). Cornet stops in 32′ are also known, as they are able to approximate the sound of a 32′ reed stop without the using pipes of the same bulk or expense (as used for example by John Compton at Wakefield Cathedral, England).
Sesquialtera stops can be solo or chorus stops. The British Victorian Sesquialtera was often the only Mixture stop on a given department (usually the Great or Swell organ; rarely the Choir organ), typically starting at 17.19.22 and then breaking back to 12.15.17 further up the compass and intended to be used in the chorus to help blend reed and flue stops together. By contrast, the Dutch, German and Scandinavian Sesquialteras of the seventeenth and eighteenth century were solo stops (typically 12.17), often (though by no means exclusively) found in the Rückpositiv division, from whose gallery-edge case position they could project a solo line well into acoustic space against an accompaniment using stops in the main organ case; such Sesquialteras are therefore particularly associated with Lutheran chorale-based organ repertoire.
Sesquialteras are often distinguished from Cornet stops because whereas Cornets (especially French examples) use wide-scaled, flute-toned pipes, Sesquialteras were generally made from narrower, principal-toned pipes (though this distinction is somewhat less widely observed in 20th-century organs than earlier organs). Sesquialteras therefore often have a sharper sound than Cornets.
This is an example of a pipe organ stoplist, showing both common stop names and conventional formatting. Within each division, flue pipe are listed before reed pipe, then low to high pitch, then louder to softer stops within a pitch level. Separate celeste stops are next to their corresponding normally-tuned stops. Reed pipe are often labeled in red on stop knobs or tabs.
GREAT
Prestant 16′
Prestant 8′
Gemshorn 8′
Chimney Flute 8′
Principal 4′
Harmonic Flute 4′
Twelfth ′
Super Octave 2′
Mixture IV
Trumpet 8′
Clarion 4′
Tremulant
Swell to Great
SWELL
Bourdon 16′
Open Diapason 8′
Stopped Diapason 8′
Salicional 8′
Voix Céleste 8′
Octave 4′
Röhr Flute 4′
Nazard ′
Block Flute 2′
Tierce ′
Cymbale III
Contra Fagotto 16′
Trompette 8′
Hautbois 8′
Vox Humana 8′
Tremulant
PEDAL
Subbass 32′
Open Diapason 16′
Subbass 16′
Lieblich Gedeckt 16′
Octave 8′
Bourdon 8′
Choral Bass 4′
Rausch Quinte II
Posaune 16′
Tromba 8′
Great to Pedal
Swell to Pedal
Percussion stops (often referred to as "toy counters" or "toy stops"), unlike other organ stops, are not , but actual embedded percussion instruments (although they may still be actuated by the wind supplies of an organ). Both tuned and untuned percussion stops exist (for instance, marimba and snare drum, respectively). They are commonly designed to imitate orchestral or band instruments, or to imitate non-musical sounds (for instance, thunder), or to produce unique sounds (for instance, zimbelstern). Percussion stops are particularly common in theatre organs, which were generally made to accompany .
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