"Cipher" ... that word in the glossary of organ playing that's virtually synonymous with "mishap" ... is the term applied to a note that won't stop playing, a defect resulting in the continuous sounding of a pipe, the key of which has not been depressed.
This is a meaning that will not be found in most, if not all, dictionaries and refers to a pipe that gets stuck "on" because the air valve (pallet) is stuck open; that particular pipe sounds and won't turn off.
Although rare, this eventuality could happen during a practice session, while accompanying a vocal soloist, while accompanying a choral anthem, while leading the hymn singing, or even during a recital or recording session, after a certain key is depressed and released; it can also happen without depressing a key at all, as when the organ is turned on and a stop is pulled.
On a mechanical action organ the key itself may also stick down with a cipher, but typically this doesn't happen on an organ supplied with electrically assisted action.
Organists always have to be faced with the possibility that when they get to the worship center, auditorium, theatre, recording studio, or whatever the venue happens to be, that something like this can happen with the pipe organ.
So, if we play a pipe organ, it may take a long time but sooner or later we're going to get a cipher.
There are 2 kinds of cipher in organs: 1) the simple (or wind) cipher, which is generally caused by sticking or dirty magnets or armatures or, more rarely, valve problems, and 2) the relay cipher, which has the same root cause and results in a continuous electric charge to one or more chest magnets, thus causing the respective pipe(s) to sound.
Aside from a potential wiring issue, organ pipes and wind chests are sensitive to temperatures and humidity; right on time, with the onset of cooler weather, organists can experience a stuck note.
Sometimes we can un-stick the air valve from the console; we can try playing the note over and over again, repeatedly sending an electrical signal to the valve.
We can also try mashing down a bunch of notes at once, with lots of stops open; this both sends a signal to the pipe and takes some of the air pressure off that particular note because it's going to a lot of other notes.
Both of these attempts speak to trying to wiggle the air valve on the stuck note, and sometimes it will work.
The obvious quick fix solution is: just don't use that stop ... try to find it as quickly as you can and keep its drawknob retired.
If the ladder must come out for a trip to the inner sanctum, there are a few quick fixes ... in the case of a flue pipe, a piece of paper, dry wash rag, or towel can be gently stuffed into the mouth of the pipe, the pipe (if it's a small one) can be gently pulled out of the wind chest, or the offending pipe can be lifted out and reseated with a small piece of paper underneath, blocking the air flow.
In the case of a reed pipe, if all else fails, it may be necessary to shove the tuning wire down into the boot to close off the shallot completely, thus creating a "dead note" until the builder can come and fix the problem.
Finding the right pipe requires a little detective work, but it isn't rocket science; we can know if it's a metal or wooden pipe from the sound (timbre), and we can know it's approximate size from the octave where the cipher is located, and we will also know which divisional chamber in which to do our searching; if moving the Swell shoe affects the loudness, then the cipher is in the Swell; if moving the Choir shoe affects loudness, we should check the Choir; if there's no change in loudness, then we can suspect the Great or Pedal; by following our ears we can know where in the organ chamber to look.
We try to match the pitch by playing various keys; this is done slowly so we can keep track of the right key, since pressing it may fix the cipher; when we're not sure which key we pressed, then the builder doesn't know where to look to find the problem.
We try to find the right stop, and thus the right pipe, by turning off all the stops; if the cipher goes away, we make a note; we then go through all the stops one by one to determine which one causes the fault.
If turning off the stops doesn't make the cipher stop, we can still go through the stops one by one to find which stop is ciphering.
We need to be careful not to move tuning slides while looking for a cipher; touching the top of a pipe, especially moving the tuning slide (or stopper if it is a stopped wooden pipe, cap if it is a capped metal pipe), makes it out of tune.
We can best find the offending pipe by blowing across the top of the pipes (blowing into a pipe causes it to stop playing), blowing into the mouth of a pipe, lightly dragging a dollar bill across the tops of the pipes (paper money is too light to move a tuning slide), or sticking a piece of paper into the pipe mouths.
There are some safety concerns if we find ourselves doing this; well meaning people can get seriously injured if they don't know what they're doing when they're crawling around an organ chamber searching for a ciphered pipe.
Firstly, we need to protect our hearing and either stuff our ears with lambs wool ear plugs or wear standard external ear protection before entering the organ chamber; big reeds on high pressure wind have a tendency to cipher more readily than other stops, and crawling around for several minutes approaching a ciphered Trumpet, Tuba, or Bombarde pipe without ear protection can be deafening and produce permanent hearing loss.
Secondly, we need to use enough light; when it comes to searching for something, we can't do well what we can't see well.
We need also to be careful and deliberate to keep our balance on ladders and when walking wooden scaffoldings; falling into a crowd of metal organ pipes from above is like landing in a hole full of spears and getting impaled ... trauma and serious medical complications can result.
We need to wear rubber sole shoes and refrain from going into the organ chamber wearing our organ (leather soled) shoes; organ shoes are made to slide on pedal keys, not grip wooden planks or the rungs of ladders.
The organist should also be cautioned here (there are so many cautionaries in music) that if it hasn't already been done, and whenever there is time, that it's best to seek permission from the officials to enter the organ chamber before any adjustments are attempted.
Seeking informed consent is always better than being reprimanded afterwards.
The story about J.S. Bach as a young, ambitious, high-strung, and creative youth having to learn this the hard way during his Arnstadt years is well known ... we recall that part of the responsibilities specified in his contract as organist there was to maintain the new organ (which would include the management of any occasional ciphers), which he did, but he was also scolded by his Church Council for, among other things, overstaying a leave of absence (he left a cousin of his, a very capable musician who wasn't even being paid, to sub for him), for bringing a young woman into the organ loft to make music (women were not allowed to sing in church back in that day), and for confusing the congregation by mingling too many "strange notes" into the preluding on the hymns, all "without permission."