Flutes

Flutes are the most prevalent pipes in most organs. They come in every pitch level and appear in every division of the instrument. They are wider in scale than principals, and may be made of wood or metal. They may also be stopped and therefore half length. Harmonic flutes are double length with tiny holes in the middle of the pipe bodies. The air column thus divides in the middle, making the sound an octave higher than that of an open pipe. Flute stops sound like real flutes or like recorders. Flutes are called Flute (in whatever language and with various prefixes, such as "Hohlflöte"), Gedeckt, Bourdon, and Pommer. A Quintadena is a stopped flute voiced to sound prominently the harmonic an octave and a fifth above the fundamental. It has a soft but unusual tone because of this. (Strange fact: a Stopped Diapason is actually a flute.)

Strings are narrow in scale and made to be rich in upper harmonics. They are not nearly as common as flutes or principals. In fact some organs do not have string stops. They are usually called Viola da Gamba, Salicional, Voix Céleste. Any stop with "Celeste" in its name has a special function. This rank of pipes is tuned slightly sharp to cause beats with another similar rank at standard pitch. This causes an undulating effect, which was very popular with romantic composers. The Celeste rank must be used with its companion rank (usually Gamba) and not used in other combinations. Sometimes both ranks are found on one stop knob (usually with a 11 on it, showing that the knob pulls two ranks of pipes). it is possible to make a flute céleste as well as a string celeste.

There are some flue stops that do not fit neatly into these categories. These hybrids sound somewhere between string and flute tone and are usually called Gemshorn or Erzähler. They may also have celestes.