Organ stop
The phrase "pull out all the stops", 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.
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.
Borrowing or duplexing refers to one rank being made available from multiple stop knobs, often on different manuals or pedal.
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.
Part of an organist's training is to detect unification and duplexing and to create registrations that take them into account.
[3] Nonetheless, heavy unification can create issues for visiting artists with limited practice times, or those improvising compositions.
[4][citation needed] 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.
An organ stop uses a set (rank) of pipes of graduated lengths to produce the range of notes needed.
For example, a stop labeled 2+2⁄3′ (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 or ters on some organs]) (1+3⁄5′) and sixth (G) (larigot, nasat) (1+1⁄3′), with rarer examples from higher in the series, such as the "septième" or "septima" (1+1⁄7′) and "none" (8⁄9′).
Mutations usually sound at pitches in the harmonic series of the fundamental, and except when derived from unified ranks, are always tuned pure.
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.
Certain stops called mixtures contain multiple ranks of pipes above unison pitch, usually octave and fifths.
For thirds, the 14 cent discrepancy between the just and equal tempered interval is large enough to introduce noticeable beating in chords, and tierce mixtures became uncommon with the abandonment of meantone temperaments.
A cornet will always contain the fifth and major third, and, depending on the number of ranks, may contain octaves, and more rarely the minor seventh, and ninth.
A Sesquialtera (or Sexquialtera) is similar to a Cornet in that it always contains a fifth and major third (justly tuned), though they normally extend to the whole range of the compass.
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).
Bourdon 16′ Open Diapason 8′ Stopped Diapason 8′ Salicional 8′ Voix Céleste 8′ Octave 4′ Röhr Flute 4′ Nazard 2+2⁄3′ Block Flute 2′ Tierce 1+3⁄5′ Cymbale III Contra Fagotto 16′ Trompette 8′ Hautbois 8′ Vox Humana 8′ Tremulant
Percussion stops are particularly common in theatre organs, which were generally made to accompany silent films.
