A Closer Look at the Pipes

Pitch Levels of Stops

On the piano, the keys always play the same pitch. Middle C will always sound middle C. The organ is quite different. Different stops are made to sound at different pitch levels so it is possible to play middle C and an octave above middle C at the same time, even though the organist is pressing the middle C key only. Chances are, when you hear organ music that is full and rich, as in a Bach fugue for example, the organist is using stops of several pitch levels.

Pipe Length and Pipe Pitch

Keyboard Diagram Showing the Pitch Level of a 32' Pipe

Organ pipe pitch levels are named according to the length of the pipe needed to produce the pitch. Pitch levels can be as low as 32' (pressing middle C sounds a note two octaves below middle C) and as short as 1' (pressing the middle C key sounds 3 octaves higher. The pipe lengths are progressively shorter as the notes go up the scale. If all the pipes in the stop were the same length, they would all sound at the same pitch. The stop pitch level is labeled according to the length of the lowest pipe in the rank, which is CCC (two octaves below middle C). In a 32' stop, the lowest pipe, controlled by the left-most key on the organ is 32' long and sounds two octaves lower than the pitch that the same key on the piano would sound!

Keyboard Diagram Showing the Pitch Levels of an Open vs. Stopped Pipe

The pipe length is also affected by the kind of pipe: open, stopped, or tapered. In the lowest note of a 32' open pipe, the pipe really is 32' long. A stopped pipe produces the same pitch as an open pipe when it is half the length of an open pipe. The lowest note of a stopped 32' stop is really only 16' long. The length of tapered pipes is in between the length of open and stopped pipes. It varies from stop to stop because it depends on the gradation of the tapered part. Why not just call it a 16'? The organist needs to know what pitch will sound. The builder decides if the stop will use open, stopped, or tapered pipes. It would be very complicated for the organist to find out what kind of pipes are used on every stop for the organ. It is easier to label the pipes according to the sounding pitch, but the label corresponds to the pipe length of an open pipe.

The Different Pitch Levels

With a range of 32' to 1', how does the organist keep track of all these pitches? The point of reference, or the fundamental pitch, is the 8' pipe. This means that middle C on the piano equals middle C on the organ only when the organist is using an 8' stop. When a pipe's length is cut in half, the pitch sounds one octave higher. Middle C in a 4' stop sounds one octave higher and a 2' stop sounds 2 octaves higher.

Keyboard Diagram Showing All the Pitch Levels

The different pitch levels are as follows: 64' (It sounds one octave below the 32' and there is no corresponding note on the piano if middle C was played. It is a rarely used stop.), 32', 16', 10 2/3' (rare), 8', 4', 2', 2 2/3', 2', 1 1/3', 1 3/5', and 1'. There are also stops labeled as Roman numerals, such as III or IV. All of the whole numbered stops sound at octaves which means that if you play middle C using a 16', 8' and 4, you will only hear the note C, but at three different pitches levels. Most of the stops on the organ sound at octaves with the fundamental note. This is crucial because the music would be very dissonant if playing the middle C key would sound a C and a B. Stops labeled with a mixed number or a Roman numerals do not sound in octaves but are not dissonant with the fundamental note.

Mutation Stops

Keyboard Diagram Showing the Pitch Levels of Mutation Stops

Mutation stops are labeled with a mixed number, such as 2 2/3', and produce a note that is in harmony with the fundamental. However, it is not the same note name as the fundamental so playing middle C does not yield the note C at a different pitch level. Mutations give the organ a rich, bright sound. Stops with 3 as the denominator of the fraction always produce a fifth above the fundamental note. This means that playing middle C, using a 2 2/3' or a 1 1/3' will always produce a G. This applies to any note. To figure out the fifth, simply count up 7 keys on the keyboard (black and white keys). The seventh note from the starting point is the fifth of that note. Stops with a 5 as the denominator will produce a third above the fundamental, or playing middle C will produce an E. To figure out the third, count up 4 keys from the starting key. The mutations do not actually sound a simple fifth or third above the fundamental but usually sound above the 4' pitch level. The 2 2/3' will sound in the octave between the 4' and 2' pipes, or one octave and a fifth above the fundamental. 1 1/3' and 1 3/5' stops sound between the 2' and 1' pitch levels. If the mutations sounded closer to the fundamental or 8' pitch, they would not produce the sparkle which makes them so wonderful. Principal pipes are most frequently used in mutations.

One unique mutation stop is the 10 2/3'. This is not frequently seen on today's organs. It was used in combination with a 16' to produce the sound of a 32' stop. The note did not sound the same exact pitch as the 32' but it gave the same musical effect and was useful in rooms whose ceilings were not tall enough for a 32'.

Compound Stops

Stops represented by Roman numerals, or compound stops, actually have more than one pipe sounding per note. These stops are the exception to the one pitch equals one note rule. The Roman numeral indicates how many ranks are in the compound. If it is a III, then 3 rows of pipes are used in that compound. This means that three pipes speak when one key is pressed. The pipes sound in combinations of fifths, thirds, and octaves with the fundamental. There are several different ways to arrange compounds with the same number of ranks so it is up to the builder to design the compound. Compound stops range from II to V. They add brilliance to the top of the sound and are used with 8', 4', and 2' stops. Like the mutations, they sound much higher than the fundamental.

One organ I frequently play on has labeled its compounds in the following way: IV Fourniture 1 1/3' In spite of the mixed number after the sound label, this is not a mutation. Four pipes are speaking at once to produce the sound. The 1 1/3' means that the lowest pipe in the group of four is speaking at the 1 1/3' pitch level which is between a 2' and a 1'. Compounds are frequently referred to as mixtures. For some sample names, see the Principals section in Sound Characteristics of Stops.

I hope you have gained a better understanding of organ stops and pipes. Please send me your questions through e-mail. Visit the Additional Information About Pipes page to learn how room space affects the pipes, what registration is, and other interesting facts.

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This site is part of the Pipe Organ Education Project. © Copyright 1996-2001 by Marya J. Fancey.