8' Open Diapason. (Pronounced DyerPayson) This is the foundation sound of the organ, (the organ's own sound if you like).
The '8 foot' part tells you the length of the longest pipe (usually a set of 61) and that middle C will sound the same pitch as it would on a piano. The 'open' part means that the top of the pipe is left open (like the top of test tube).These pipes are usually made of metal..

8' Leiblich Gedackt. Literal translation is 'lovely covered' This stop can be made made of wood or metal and has a flute like quality to its sound. The pipes are 'stopped' (like a test tube with a cork in the top), hence the word Gedackt.'covered'.

8' Salicional. The name is derived from 'Salix' meaning willow. Salicis Fistula means 'willow pipe', a rustic flute made from a branch of a willow tree. Although originally a flute like tone, over the centuries this open stop now gives a delicate string-like tone.

8' Voix Celestes. Literal translation is 'Heavenly voice' and is bascally the same string sound as the Salicional, but slightly detuned so that when used together they produce an undulating effect. The TC means that there are no pipes for the notes below Tenor C. (The C below middle C.)

4' Viola. The length of the longest pipe on this stop is 4 feet. Viola is the sound produced (not the actual instrument. Try putting a 4' viola under your chin!).
If you tap a metal rod it will sound a note. However, it was Pythagarus that discovered that if you halve the length of the same rod, and tap it, it sounds a note exactly one octave higher. The 4' viola has a very similar sound to the Salicional, but when you press a note, the sound produced is an octave higher.

4' Flute Harmonique. (Harmonic Flute) This stop has a flute like tone and sounds an octave higer than the note played.
Hence the 4'. However, the longest pipe is actually 8 feet long! Let me try to explain. If you've ever tried playing a recorder, you'd have noticed that if you blow too hard it sort of squeals and plays a note much higher. This note is what's known as an harmonic. Usually the note produced is an octave higher. This is known as the eighth harmonic. With a Flute Harmonique, the pipe length is doubled, but the wind pressure is increased to over blow the pipe and make it produce this harmonic. (Phew).

3rks Cornet 12-15-17. This type of stop is known as a "Mixture" Hmmm. OK. 3rks? This means even if just this one stop is selected, three lots of pipes (called ranks-hence rks) will sound at once. Now to deal with the three numbers. Imagine we press middle C the three notes that will sound will be the 12th harmonic (G an octave and a half above middle C, 15th harmonic (Bb above that G) and the 17th harmonic (C# above that Bb). Now on its own, this stop would sound like 3 people leaning the recorder all playing at once. However, when used in combination with the 8' and 4' stops, it adds brightness to the overall sound and you don't really hear the individual harmonics at all. As for the name 'cornet', it's not meant to immitate the modern trumpet like brass instrument but rather the Renaissance instrument known as a cornet or zink. This was blown in the manner of a brass instrument, but made of wood, and with finger-holes similar to a recorder.

16' Contra Oboe. Now we're getting to the big boys. The longest pipe is 16 feet long, half the length of a bus. Going back to our metal rod, we know that half the length of the rod plays a note an octave higher. If we could double the length of rod then it would produce a note an octave lower. Playing middle C will produce the next C note down. (Tennor C). The Oboe stop is a Reed Stop. The sound is produced by blowing air over a metal reed. (as in the harmonica or accordion).

8' Corno-di-Basso. This is another reed stop similar to a clarinet but thicker in tone. If you listen to "To a Wild Rose" on the main page you hear the main melody using this stop.

The last four stops are known as a Non-Speaking stops.
These don't produce a sound of their own, but add an effect to the sounds that are already selected.

Tremolo. This gives a slight wobble to the sound.
(The main difference between a classical or concert organ and a cinema organ is that cinema organ tends to use the tremelo nearly all the time and is much more wobbly.)

16' Swell Sub Octave. Selecting this stop adds a note one octave lower to the note played.

4' Swell Octave. Selecting this stop adds a note one octave higher to the note played.

Swell Unison Off. Selecting this stop takes out the sound of the actual note played. (leaving the notes that are coupled)

e.g. If the 8' Salicional is selected, by adding 16 Swell Octave coupler, a Salicional will be added and octave lower. If the Unison Off is then selected, ONLY the 16' will sound.