Electronic organs and virtual pipe organs are being built today which have the technology to generate sounds in real time without digital sampling and the ability to tune each register, or rank, and in some cases every individual note within that rank, separately from every other.
During the 90's however some electronic organs were built with sampling technology which would not permit individual tuning by stop or by note.
In these instruments the pitch of the Great division was factory set at A4 = 440; separate controls were then provided to adjust the pitch of every other division slightly up or down from that or to move the general pitch of the Great up or down slightly, if desired, to suit the tuning of other live keyboard instruments or perhaps a MIDI connected software download of a Hauptwerk upgrade sampled organ tuned to, let's say, A4 = 446 [See blog, Virtual Pipe Organ (VPO)].
Separate pitch controls for these divisions and a general pitch control were provided in a hard to reach place, often underneath the bottom manual and all the way to the back (photo) where, typically, only the organist knew where they were and these controls, once set, would remain undisturbed.
Rotating these small controls clockwise sharpened the pitch; rotating them counterclockwise flattened the pitch.
The way this was tested was by drawing the Great 8-foot Trumpet and an 8-foot reed in every other division and then coupling the division to be adjusted to the Great; by holding down some note on the Great such as the tenor F3, the resulting beats between the Great and the division being adjusted could then be detected clearly.
The authentic sound of a pipe organ has to do, partly, with the fact that the sound is acoustically coupled to the air in the room and each register, or rank, of pipes, and each individual pipe within that rank, has its own separate tuning; some or these pipes are dead true in pitch, some are very slightly sharp, and some are very slightly flat; in this respect, each one of these pipes has its own personality.
When the sound of all of these pipes are combined, the random chorus effect which results is the same we hear in a chorus of dozens of singers, a large band, or a symphony orchestra; the notes are all there, right on pitch, and yet so very slightly different in pitch from every other that the listener's ear recognizes this as something vibrant, alive, and breathing, something we can listen to for hours on end and never get tired of it.
In an electronic organ we have a different situation; the sound, being produced by loudspeakers, is not acoustically coupled to the air in the room, and every note of every stop can be engineered so dead true in pitch that the wonderful chorus effect that our ear associates with the real McCoy can be completely lost.
Engineers therefore have sought ways to overcome the limitations of loudspeakers and digital sampling technology in electronic organs to create, albeit artificially, this desirable and most necessary random chorus effect.
The entire success of an electronic organ tunable by division stands or falls upon the fine tuning and setting of these little pitch controls; they will make or break an organ like this.
In a 5 manual console where the pitch of the Great is fixed, a good scheme for tuning by division is to adjust the Pedal almost true but just very slightly sharp to the Great, then tune the Swell and Echo very slightly sharp by different amounts; the Choir/Positive and Solo can then be tuned very slightly flat by different amounts, remembering that the ear can tolerate a little sharpness but will not tolerate the same degree of flatness.
When everything is coupled together this way a chorus effect is generated, and, in this kind of organ, having it makes all the difference in the world.
Also, in an organ of this kind where the player can be tasked to use every means possible to create an authentic sound, we might also consider introducing an undulating rank or two, if it isn't too strong, into the full organ ensemble.
We need to remember here, as always, when we're playing a real pipe organ, that undulating (mistuned celeste) ranks are never drawn with the full organ.
But with an older electronic organ, in situations where the player is searching for every possible means of creating the best chorus effect with the full organ and the most realistic sound possible, it may help to throw in a soft 8-foot String Celeste or Erzahler Celeste tuned slightly sharp, or maybe the Unda Maris stop tuned slightly flat, or maybe both, to provide that little bit of extra shimmer lacking in the recipe, provided that in so doing it blends completely into the ensemble and loses its identity.
Some judgment and good taste is needed here with the ear being the final judge over the sound; if the celeste or Unda Maris rank causes any detectable wobble in the full organ sound where it can't seem to hide among and disappear within all the other stops, it should by all means be left out.
Purists may want to grab this author around the neck and shake him for even suggesting that an undulating stop might be thrown in with the full organ, but when we're seeking an authentic sound and we're working with an electronic organ with older technology that's tunable only by division, we have to do everything we can, using the full resources of the instrument at hand, such as they are, to get the listener there.
You simply adapt your way of working to fit the situation [See blog, Guidelines With Registration].
As with the rules of part writing, so goes the rules of organ registration: life improves dramatically when someone breaks a rule and finds beauty when he was told, or led to believe, that there was none [See blog, Getting Started With Writing, Part XX].