  Pipes and Stops |
Introduction
One of the notable characteristics of the organ as a musical instrument is its ability to produce sounds of different timbre. Although there are indeed tone colors which are associated in most minds with the sound of an organ, the instrument can also produce many sounds that are imitative of other instruments. All of the different sounds of the organ are made by pipes - - often the most visible as well as audible part of the instrument. For the organist one of the challenges of the instrument is to learn about both the different timbres (tone colors) available and the names of the "stops" that produce those sounds.
In general we use the term "stop" to refer to a method of controlling which pipes speak when keys are played. We also use the term in a more specific way, when we refer to the actual control itself -- usually a drawknob or a stop key -- as a "stop." The context in which the word is used can usually clarify what is referred to at the time -- the sound or the control for that sound. To make matters more complicated, there are two sub-types of stops that the student will encounter.
- Half stops control a short register -- one that does not extend the full compass of the keyboard. In most applications -- a Cornet V, for example -- the stop will sound only in the upper octaves of the keyboard, often beginning on c1. Many instruments built in the last quarter of the twentieth century have such a stop on the Great division.
- Divided stops provide two stops for a single register or rank of pipes. One stop controls the lower octaves of a keyboard, the other the upper octaves. This arrangement is most often found on very small instruments, where the player might want to play one timbre in the left hand and a different one in the right hand, but only one manual is available.
Timbre
A description of timbre is often difficult to either devise or understand. In English, such terms are most often borrowed from words that describe other sensory input as well, or they describe emotional characteristics that bring a specific sound quality to mind. Thus we might speak of a "bright" or "dark" sound, and it is generally understood that the phrase "an angry voice" means something rather specific about timbre and dynamic level.
At times, a more technical description is attempted, one that describes the relationship of overtone to fundamental. It is possible even to provide an analysis and accurate measurement of the relative strength of the fundamental pitch and its overtones, the physical characteristics of a sound wave that actually determine timbre. Except in the most general sense, however, these descriptions are better used for technical rather than musical discussions. Understanding the principle is necessary, but applying the concept has limited value, except in discussions of the physical properties of different timbres.
In general the name given to an organ stop describes the timbre of its sound. When that name includes an Arabic numeral, the pitch level of the stop is identified.36 Sounds produced by organ pipes have a wide range of tone colors, some of them imitative of other instruments and others unique to the organ. In some cases a stop name is borrowed from the name of another instrument, such as a Clarinet. One would assume - - correctly - - that the stop should produce sounds like those of the orchestral instrument. Other stop names, however, may carry no such connotations. There is no orchestral instrument called a "Diapason," nor is there to be found a "Gemshorn" in modern wind ensembles.
Therefore, in order to understand what sounds a given stop will produce, one must be familiar with stop names and their associated timbres. These names, however, often appear to be infinitely varied and confusing. A complete list of all the stop names found on organs the world over would be prohibitively long, and no one could expect to hear and learn to recognize them all. Nevertheless, an important part of understanding the instrument is learning to distinguish sounds based on the name of a stop, and the timbre of any given pipe sound is determined by the way in which that pipe is made.
The process of learning the sounds of different stops is made easier by a system of classification of timbres. One approach is to assign stops to groups based on sound characteristics they have in common. The other is to describe the way in which the pipe is made in order to produce that sound. The two descriptions are of course related, and it is often the case that a single term or phrase will do both. For example, referring to a "stopped flute" describes both a tone color (different from the sound of an "open flute") and a type of pipe construction.
The only sure way to learn the sounds of stops is to hear them, and most organists spend at least some of their practice time in listening to the instrument. This tutorial includes sound files that serve as examples of different timbres produced by organ pipes, but they are subject to limitations. First they are only recordings, not the real sounds of pipes. Furthermore, the speaker systems found on most computer systems are incapable of reproducing the full audible range of even a good recording. The sound files should be heard as giving only an indication of the sounds that are made by organ pipes. If they are the student's first introduction to the topic, he or she must pursue the matter by listening to similar stops on an organ in order to really hear the different timbres.
As a student begins to learn the tonal properties of different stops, he or she must eventually learn about the pipes themselves: how their construction affects their sound, and how the different types of pipes are distributed throughout an instrument. The first step in learning about the pipes themselves is to learn the first basic division: all organ pipes are one of these two types:
Separate pages in this tutorial describe the construction and tonal properties (timbre) of each of these two types. In spite of the differences between pipes in these two groups of pipes, however, they do have similarities in the materials that are used in their construction. Materials used in the construction of both reed and flue pipes are described on a single page.
- flue pipes (often called simply "flues")
- reed pipes (often called simply "reeds")