The second kind of stops found on an organ are called the
Non-Speaking stops
Non-Speaking stops do not produce tones, as their function is to modify the Speaking Stops.
There are three basic ones found on most organs.
1 Intermanual coupling stops.
These couple one manual to another or to the Pedals. So that one note depressed on the keyboard, will sound the same note on either one of the other keyboards or the pedal board, to which it is coupled.
For example, coupling the Great * keyboard to the Swell keyboard, modifies the tone.
So Middle C played on the Great keyboard, retains the same pitch, but changes quality, when coupled to the Swell keyboard.
*See footnote
In addition the 16ft and 4ft intermanual couplers can also vary the pitch.
The pitch designation (16, 8, 4) specifies the pitch at which the division is to be coupled.
8' is concert pitch in organ nomenclature. When using an 8' coupler, the division is coupled at its normal pitch.
As the 4' pitch is an octave above the 8' pitch, so when a 4' coupler is used, the manual is coupled an octave higher than normal. This nomenclature is similar to the pitch designation used in organ stops.
8' intermanual couplers are commonly used when building large ensemble registrations,
whereas 4' couplers are usually not employed to do this.
However, 4' couplers are often used with Celeste stops in more gentle registrations; they effectively increase the number of notes that are sounding and increase the warmth and breadth of the ensemble.
In the next Reply we look at the second of these non-speaking stops.
Peter
* Footnote
Keyboards (or manuals) are separated so that the organist can play different sounds at the same time using the different manuals, and pedals. The manuals and pedals can also be coupled together so that both are played at the same time, with the main initiative coming from one of them. However, some smaller organs only have a single manual, with or without pedals.
Common names for manuals (or Keyboards), made in different countries, are:
America/England Great, Swell, Choir, Solo, Orchestral, Echo, Antiphonal
Or also America/England Great, Swell, Choir, Solo, Echo, Bombard, Fanfare
Germany Hauptwerk, Schwellwerk, Rückpositiv, Oberwerk, Brustwerk
France Grand Choeur, Grand Orgue, Récit, Positif, Bombarde
Holland Hoofdwerk, Rugwerk, Bovenwerk, Borstwerk, Zwelwerk