The pipes in a pipe organ are designed and labeled by two different primary factors. First is its pitch. The different stops in a pipe organ always have a number in front of them. This number refers to the speaking length of the stop. If the number is 8’, then the stop speaks the same pitch as you will hear on a piano. If the number is 16’ then the stop will speak the pitch one octave lower than the pitch on a piano. If it says 4’, it will speak the pitch one octave above the same pitch on the piano. And so on and so forth all the way down to 64’, and all the way up to 2 2/3’, 2’. 1,3/5’, 1 1/3’, 1’ and beyond.

Second is timber or color of sound. Directly following the pitch number will be a name. The name refers to the color of sound for the particular stop. In general, the colors of sound fall into two different categories. They are flue pipes and reed pipes. Flue pipes make their sound in the same way as a recorder or penny whistle. The pressurized air goes in one end of the pipe (the foot), is channeled through a small slot (the windway), and strikes a thin lip a certain distance above the small slot (the upper lip). This process starts the column of air in the body of the pipe vibrating at its given speed and producing its given pitch. Flue pips are generally subdivided into two groups, those in which the bodies are open on top (Principals and Strings), and those which are stopped on top (Flutes).

Reed pipes make their sound in the same way as a clarinet or saxophone. The pressurized air goes in the bottom of the pipe (the boot). It passes between a brass reed and brass shallot (similar to the mouthpiece and reed on a clarinet). This process starts the column of air in the resonator of the pipe vibrating at its given speed and producing its given pitch. Reed pipes are generally subdivided into two groups, those with conical resonators (Trumpet and Oboe type stops) and cylindrical resonators (Cromorne and Clarinet type stops).