When a musician is tasked with creating sheet music from a recording of an improvisation, and they write down the notes that make up that same music or instrumental solo, it is said that they have created a "transcription" -- they have transcribed to notation something that, in this case, was previously unnotated.
A transcription can also mean rewriting a written piece of music, either solo or ensemble, for another instrument or group of instruments for which it was not originally created.
A transcription therefore, strictly speaking, is not an "arrangement" -- it is a faithful adaptation, whereas the latter generally changes significant aspects of the original piece.
These terms tend to overlap in popular usage however; people speak of, for example, an organ "transcription" of Claude Debussy's Claire de lune from his Suite bergamesque for piano, "arranged" by someone.
A control provided to certain very large church organs and most large concert organs is the Pedal [Treble] Separation tilting tablet.
This control, also known as a Pedal Divide, permits the player more freedom in playing transcriptions -- it splits the sounds available on the pedals, usually at tenor C, by giving the 13 lower notes of any drawn Pedal stop, the rest of the pedalboard sounding any manual to Pedal coupling.
This control therefore is wired to silence the Pedal stops above the split point, usually at tenor C, and silence the coupled manual stops below that, to free the right foot to play its own instrumental part on the pedals.
Because of the multiplicity of orchestral parts -- in an orchestral piece there may be as many as 2 dozen separate instrumental parts being played simultaneously -- it becomes problematic to reduce this music to what a single organist can manage to play; the purpose of this control is to supplement the technique of thumbing down on a lower manual to give as many instrumental parts as possible, if not the entire composition.
Sometimes the split point is adjustable, but it needs to be near the low middle compass of the pedalboard with the divide favoring a wider compass for the right foot so it can better carry its own melodic line (when the split point is non-adjustable it generally defaults at tenor C).
When this control is adjustable a "set button" for the Pedal Separation will be provided; the organist simply holds down the pedal key where the split point is desired, and, while holding down the key the button is pressed, and the new split point is set; Pedal stops would then play below that point, and above it would be whatever stops are coupled from the manuals.
This allows 4 different tone colors to sound without thumbing down across manuals [See blog, Thumbing Down] -- one in the right hand, one in the left hand, one with the right foot, and one (the bass) with the left foot.
The instruments at Gloucester Cathedral, Truro Cathedral, and Ripon Cathedral in England are all equipped with this control, and there are several examples from American organ building including, most notably, the monumental Wanamaker Grand Court organ in Philadelphia and in other instruments built for auditoria where organ transcriptions were very popular a century ago.
When this control is provided to an organ but very seldom, if ever, used these days when transcriptions are performed, or if it should become unreliable over time, a guest organist may find that its tilting tablet has been rewired and relabeled to function as something else not original with the builder which may be more generally useful.
This was done with the historic Kimball organ at the Saint Louis Scottish Rite Cathedral where the original Pedal Separation tilting tablet provided by the builder was rewired as a Master Swell Lock tilting tablet allowing all of its 128 swell shades to be operable from a single Swell shoe, simultaneously.
In this instrument a Pedal to Great tilting tablet coupler was also inserted which was not original with the builder [See menu bar, Photos III, Development & Design subpage] -- here one of the four original crescendo tilting tablets [Flutes to Crescendo] previously unused was rewired and labeled to control this new coupler; the remaining three original crescendo tilting tablets [Diapasons to Crescendo, Strings to Crescendo, Reeds to Crescendo] remain disconnected and await future restoration.
In this instrument we find a most unique situation where all Pedal voices save for one rank of unified Bombarde pipes are borrowed from enclosed manual divisions whose 8-foot windchests have been extended for this purpose -- here this new Pedal to Great coupler is polyphonic, operates on all 61 notes of the Great manual, and functions very much like a French Grand Orgue subcoupler -- a control actually specified in the music of certain French composers, notably Franck and Vierne -- to provide the extra gravity needed when playing big chords for both hands very high on the Great manual.
This new coupler is also helpful to new organists who are coming to this instrument from the piano, may be hesitant to perform the pedals in public just yet, and gets them playing the whole instrument right away.
In certain instruments, both pipe and electronic, this Pedal to Great coupler is sometimes labeled "Bass coupler" or "Automatic Pedal" (A.P.) and is provided with its own reversible piston (photo).
When inserted in an electronic instrument supplied with an independent Pedal division this coupler is generally monophonic, i.e., operable on only the lowest note played on the Great and limited to the bottom 32 notes of that manual.
Also, in electronic instruments, the Pedal stops are often silenced on the pedal keys when this coupler is engaged, whereas on a pipe organ all of the Pedal stops (unless specially wired not to) will still sound there.