There are four basic groups of organ pipes that each individual stop can be sorted into, depending on their sound quality and construction. They are as follows:
- Principals (or diapasons)
The principals are the most common stops on an organ, and the backbone of almost all stop combinations. All instruments will have this type of pipe. The principals don't imitate any orchestral sounds but are the pure, basic "organ" sound.
On a console, they can be found under the name "Principal" or the German equivalent, "Prinzipal". The most common stop is an 8' one, frequently with 4' and 2' octave doublings available (which are sometimes called "Octave" and "Super-Octave" instead of "Principal on a console). Large organs will sometimes even have mutation stops like 2 2/3' and 1 3/5'. On the pedals, you can usually find the 16' and 8'.
The flutes are another common type of pipe. They are usually softer and breathier than the Principals, and higher in pitch. Common flute stops are Flute, Rohrflute, and Sifflote.
The string pipes are the softest of all the pipes.
The reed pipes are the loudest of all pipe combinations. Common reeds include the Trumpet and Bombarde.
Some organs will also feature percussion instruments. The most common is chimes, but you occasionally see things like xylophones or even bass drums (usually found on large instruments). While not technically pipes, they nonetheless merit inclusion here. They usually should not be used as part of a large chorus, but by themselves, because they don't blend in well with other organ pipes.