Beginners' Guide To The Organ, Non-organists enquire within.... Options

[Teigr]

This thread is for people who don't know anything about organs to find out how they work, what the jargon means and what all the fuss is about.
I hope some of the more experienced organists will chip in with explanations and answers to questions (and corrections, as I'm bound to make some mistakes here!) and anyone is welcome to ask anything about organs (including "could you say that again, but without the jargon?").
The only stupid question is one you don't ask.


So, getting started....

The bit of the organ that you sit at and do things to when you play is usually called the console (sometimes called the keydesk when talking about certain types of organs). The keyboards are called manuals. A typical church organ will have 2 or 3 manuals, and a typical cathedral 4 or 5, but you can find instruments with anything from 1 to 7.
Most organs have a pedalboard. This is a bit like an oversized keyboard, played with the feet.
Most have one or more expression pedals. For the time being, think of them as a variable volume control. They are large tilting pedals set just above the main pedalboard, somewhere near the middle of it. (edit: Usually! On some instruments they are set to the far right.)

Somewhere near the manuals, you'll find the stop controls. Drawstops are knobs that you pull out and are the most usual sort to find on a church instrument. Tab stops are sort of flat switch things that you flip downwards. Either sort will be labelled, most with a number and a name.
The most usual place to find drawstops is on the jambs either side of the manuals. But some organs have them just above the uppermost manual.
Just below the keys, you'll probably find a series of little buttons on the front edge of each manual. These are called thumb pistons.


Imagine a large box, full of pressurized air. Imagine it has 61 holes in it, in a row. Each hole is covered and has a simple pipe (a bit like an upside-down recorder without any finger holes) directly above it, each one slightly smaller than the one before it (so it will give a higher pitched note if air flows through it). The widget (let's call it a pallet) that covers each hole is connected to the corresponding key of a 5-octave keyboard. When you press the key, the pallet moves out of the way and air can flow into the pipe, so that the note sounds.

That's the basic idea of how an organ works.
Each set of 61 matching pipes is called a rank.

Different types of pipes make different sorts of sounds.
So, you'd like to have several different sounds available for each note, which means several sets (ranks) of pipes.

Do you remember the game Stay Alive, with marbles resting on top of two sets of sliders (at 90 degrees to each other)? Each slider had holes in various places, but a marble would fall though only when both sliders were set so that they had a hole underneath the marble?
Organs are like that - to make a pipe sound you need to open two things. A slider (controlled by a drawstop) and the pallet (controlled by a key). If you've got both open, air can move through into the pipe and make a sound.
Until you draw a sounding (or speaking) stop for the manual, you can press the keys as much as you like and you won't get any sound.

Several ranks of pipes, grouped together and intended to be controlled by one manual, are called a division.
Most organs have one division for each manual and one more for the pedals.
This means that each manual has it's own collection of available sounds, and you can play with contrasting sounds by using one hand on one manual and the other on a different one. Or you can change back and forth between different manuals as you play.
You can also change the sounds by selecting different stops (and you can do this while you're playing, but it takes a bit of practice).

On a two-manual organ, the divisions are normally called Great and Swell.

All the pipes of the Swell division are inside a box, with louvred shutters on the front. If you close the shutters, you've basically shut the entire division away inside a closed box. This muffles the sound and makes it seem quieter to the listener. If you open the shutters gradually, you get a crescendo.
You control the position of the shutters using the swell pedal (which is an expression pedal). This is the volume control I mentioned earlier. You're not really changing the volume of sound the pipes produce, but you're changing how much of the sound you allow out of the box.
On a three-manual, the extra one is usually called the Choir and may, like the Swell, be an enclosed division (i.e. be in a box, with a pedal to control the shutters). In this case, the Swell and Choir divisions will be in two /separate/ boxes, and the console will have two expression pedals.

Some organs have more divisions than they have manuals. When this happens, two divisions share a manual and there will be one or more drawstops to control which is active.

If you have 4 divisions, the 4th might be Solo or Positive. If you have 5, you'll get both of those.
I'm sticking with the English names here for the time being. Foreign organs not only have different names, but the character of the divisions may be different, so it's not just a case of translating the names.

Unlike the piano, you can't affect the volume by how hard you strike the keys.
You've got two ways to change volume - open and close the swell box, or add and subtract stops (ranks). The more pipes you use at the same time, the more noise you'll make.
Some ranks are much louder than others, so for a quiet hymn you'll choose different stops than for a loud one, and then you'll add/subtract from there to create a little bit of variety between (or during) verses.

You can also engage things called Couplers which allow you to control the pipes belonging to one manual from a different one. These have names like "Swell to Great" and "Great to Pedal". They are controlled by drawstops, much like sounding stops (ranks) are.

The choice of stops, manuals and couplers that you're going to use for a given piece of music (and you might use several different set-ups within one piece) is called registration.
All the fussing around that you do while playing, aside from actually playing the notes, is known as organ management. (Changing stops, changing pistons, changing the expression pedal(s), changing manuals, etc.)

Explanation of stops (types (flues (flutes & diapasons) and reeds), names, lengths, mutations, etc.) to follow another time, along with explanation of the different types of action and the question of how the box full of air (windchest) works.

Ask if anything isn't clear. Chip in with corrections and clarifications if you've got any (note: I've deliberately simplified a few things).

T.

[Teigr]

If anyone wonders why I started this thread, take a little look at:
http://forums.abrsm.org/index.php?showtopi...26&st=98895
That's a page from the CISD thread that includes a couple of posts where I tried to explain a little bit about stops. I'm going to try to make it less confusing this time around, though.

Hopefully the stuff on this thread so far has laid a good foundation for what's to come.
But I'm going to start by straying away from organs for a moment, and try to say a bit about the harmonic series.
The catch here is that I've got a physics/maths/eng background, so I tend to dive headlong into physics jargon. I'm going to try hard not to, but I might need some help with trying to get this into terms that anyone can understand no matter what their field is.


When you hear a sound, you're hearing vibrations in the air, which hit your eardrum, are transferred into your inner ear and are decoded by your brain automatically.

What makes those vibrations in the air is something else vibrating (and jogging the surrounding air), or something which makes the air itself vibrate in a controlled way.

String instruments are good to use as examples, because you can see what happens. If you pluck a string you can see it vibrate.
Look carefully and you'll see if moves the most in the middle, and less at the ends (because they're fixed to the instrument).

The obvious ways to change the pitch of a note on a stringed instrument is to vary the thickness or the length of a string. The thicker strings give lower notes. And if you shorten a string (by pressing down against the fingerboard), you get a higher note.
You can also get a higher note if you tighten a string - that's how you tune a violin or similar, by adjusting the tension in the strings.

But there's another trick you can use. Get a friend with a guitar to show you this, or borrow one and try it for yourself.
Find the 12th fret (strip of metal across the fingerboard) - count starting from the end where the machine heads (tuning pegs) are. This will give you the mid-point of the strings.
Pluck a string and listen to the note. Get the sound of it fixed in your head.
Then hold the string down so that it's touching the fretboard just behind the 12th fret (your finger should be to the side where the machine heads are). The active length of the string now goes from that fret to the bridge (the place where the strings attach to the body of the guitar). Pluck the string again, and you should hear a sound that's an octave higher than you got from the open string.
Now the clever bit. Touch the string very lightly with one finger, directly over the 12th fret (so if you pressed down, you'd touch the fret itself). But don't press down. Now pluck the string. You should again hear a sound an octave higher than the open string. (It can take a bit of practice to find the knack of making this work.)

What you've done here is, instead of halving the length of the string which can vibrate, you've halved the length of each standing wave (vibration) on the string. Instead of the string vibrating as one length, it's now vibrating in two separate sections. You should see that the bits that move the most are the middle of each half of the string, while the two ends and the bit where your finger rests are still.
So it's now behaving a bit like 2 separate strings, each half the length of the original.

If you try the same trick at the 5th fret, the fretted note will be a perfect 4th above the open string, but the note when you just touch the string very lightly should be 2 octaves above the open string.

When you halve the length of a string, the sound goes up by one octave.
The 5th fret is one quarter of the way along the string, so when you fret (press down just behind the fret) there, you're not going up a full octave, as 3/4 of the string is vibrating.
But when you do the thing with the light touch, you're encouraging the string to set up 4 equal length standing waves (one between your finger and the top of the string, the other three to match it, down the rest of the string). So it's behaving rather like 4 strings, each of which is a quarter the length of the original string.
Making a string a quarter of its original length with raise the pitch by 2 octaves, because you've halved it, then halved it again.


You've probably seen a tuning fork labelled A=440.
That means that it gives the note we call A, and the vibrations associated with it are 440Hz (hertz, or wiggles per second).
Anything vibrating at 440 Hz will sound like an A, but the A you get from a violin sounds very different from the one you get from an oboe.

This is because the sound the instruments produce aren't a pure vibration of 440 wiggles per second.
The main sound is that, but there are a whole bunch of other waves as well. You can't see them when you look at the string, because the main one is the biggest.

Quick tangent - pluck an open string very gently. You can see it vibrate, but the bit that moves the most isn't actually moving very far. It should sound fairly quiet.
Now pluck it harder. It should sound louder and the amount it wiggles by should be bigger.
The "width of the wiggle" is called amplitude.

Back on track - the 440Hz wave has the biggest amplitude. The smaller waves that are happenning along the string have much smaller amplitudes, so your eye can't see them. They're like the waves you set up when you touched the string very lightly and plucked it.
Your ear hears them though. But your brain doesn't tell you that you're picking up a bunch of shorter waves (which would be higher pitched notes if you heard them by themselves). Instead, it interprets them as part of the overall timbre (type of sound) of the main A440 note.

Different instruments produce different collections of those extra "invisible" high notes - called overtones or harmonics, and that's why they all sound different even when playing the same note.


Physics jargon that you'll find useful:

amplitude - the width of the wiggle.
wavelength - the length of the wiggle
frequency - wiggles per second

Big amplitude = loud sound. Small amplitude = quiet sound.

Wavelength and frequency are (inversely) related - the shorter the wiggles, the more times they wiggle per second, and vice versa. We describe the pitch of a note in terms of frequency. But we tend to change the frequency by messing around with the wavelength (shortening strings, covering finger holes, opening valves to lengthen tubes, etc).

There's some complicated-sounding stuff about sine waves and how the wave you see on a stopped string is actually half a complete wavelength. Ignore that for now - I'm mentioning it just to reassure the physics folk. I'll try to explain it in very easy terms later (it becomes relevent when you want to understand how stopped pipes work).


The overtones that you can get aren't random. They come in a predictable pattern, called the harmonic series. I'll go into that more later when I try to explain how all this stuff applies to organs (the basic idea is that different length pipes work like different length strings).
The organ's party trick is that you can manipulate which overtones you get from it, thus changing the sound of a note. There are special stops that are used to do that, and they're known as "mutation stops" because you use them to modify the sound of other stops.

I'm going to leave it there to give people a chance to make corrections and ask questions about the physics, before getting into how this applies to the organ.

T.

[sarah-flute]

amplitude - the width of the wiggle.
wavelength - the length of the wiggle
frequency - wiggles per second

(IMG:style_emoticons/default/laugh.gif) Well done, you explained something related to physics in a way I can totally understand (IMG:style_emoticons/default/biggrin.gif) consider me impressed...

*awaiting next installment*