Posted: Wed May 17, 2006 11:26 am
Pipes, Chambers, Swell Pedals, Swell Shutters, and Unificationby Wes TriggerVery basically, Pipes are located in chambers. A pipe will speak when a keyboard key is pressed and a stop tab has been engaged. Chambers have swell shades that are opened and closed by a swell pedal on the organ to vary the volume by opening and closing the swell shades. For the most part there is only one set of pipes for a given stop name such as Tibias and this one set of pipes can be played from all manuals.An organ pipe is one of the tuned resonators that produce the sound of a pipe organ. Most organ pipes are either long cylindrical metal tubes or elongated wooden boxes of rectangular cross-section.A rank of pipes is a common group of pipes such as Tibias. Here are 5 ranks of pipe in the Solo Chamber of the Los Angeles Orpheum's Wurlitzer Style 240:There are two basic types of pipes. They are the Flue pipes and the Reed pipes. Whistles or Fipples drive flue pipes. Most organ pipes are flue pipes. Flue pipes are themselves divided into three broad classes:Flute pipes have the purest tones, and are generally the widest. Flutes and Tibias are examples.Diapasons are intermediate in tone, and are the basic sound of the pipe organ. The Diaphonic Diapason and Horn Diapason are examples. String tone pipes have the richest harmonics, and tend to be the narrowest pipes. The Viol d’ Orch and Viola are examples.Reed pipes are those driven by a beating or a vibrating reed. Some examples of reed pipes are the Vox Humana, English Post Horn and Tuba.There is another way of dividing pipes into two broad classes:Open pipes are open-ended. These pipes when blown are rich in harmonics. These pipes include some Flutes, Strings and some Diapasons as well as most reed stopsStopped pipes, also known as closed or gedackt (from the German for covered) are closed at the end opposite the reed or the fipple. These pipes are not as rich in harmonics as are the open pipes. A closed pipe is almost exactly half the length of an open pipe sounding the same note. These pipes include the Tibia, the Lieblich Flute a stopped flute and the Quintadena. There are also closed Diapasons.Stopped pipes are used for two main reasons:They tend to be gentler and sweeter in tone. Some builders refer to any stopped flue pipe as a flute. Stopped pipes for deep bass notes that would otherwise be difficult to fit into the organ chamber are more easily accommodated and also cheaper to build. An 8’ stopped pipe will sound at 16’. In some organs, the bass notes of an otherwise open rank of pipes are stopped for this reason alone.Now that we know something about pipes we can explore how they work in a TPO.Pipes are located in rooms called chambers. The usual arrangement is that the Main chamber appears on the left and the Solo chamber appears on the right. A blower furnishes large quantities of air to the pipes. When a manual key press activates a pipe the air causes them to speak. The pipes always sound at a constant volume level. Manipulating the swell shades provides variations in volume from soft to loud. When closed the swell shades only allow a low level of sound escape from the chamber. As the swell shades are opened the volume level increases until it becomes quite loud. From left to right, the above pictures show swell shades completely closed, partially opened and fully opened.The swell pedals control the movement of the swell shades. Forward motion of the swell pedal causes the swell shades to open. Reverse this motion and they close. The swell pedals are the two left most pedals in the photo, one for each chamber. On some organs the right most pedal can be used to control the shades for both chambers. If they can’t be coupled, one foot can operate both swell pedals. This also provides for having different volume levels in each chamber. The right most pedal is the crescendo pedal. Forward pressure on this pedal cause certain stops to be brought into play as the pedal moves forward. An increase in volume by causing stops to be engaged as the pedal moves forward and a decrease in volume as stops are turned off as the motion is reversed. Stops that were on prior to the use of the crescendo pedal remain on when the crescendo pedal is returned to its off position This crescendo pedal is raised higher then the swell pedals so that the organist does not inadvertently place a foot on the crescendo pedal.When we say that a rank of pipes is Unified we mean that a rank of pipes is not associated with any manual but can be played from all manuals simultaneously. Because a rank is selectable from many manuals and at many pitches individual ranks can function either as an ensemble rank or a solo rank. To further explain, if the Tibia 8 middle C is held down on the solo keyboard and then the same note and stop are pressed on the Accomp manual it would appear as though no note were pressed on the Accomp since it was already held down and sounding from the Solo manual. Now that we have all of this information about pipes how does the MIDITZER produce the sound of pipes with no real pipes of its own? A file of sample pipe sounds known as sound fonts contains all of the sounds used by the MIDITZER. When a stop is engaged and a key is pressed this sampled sound is selected just as a pipe would be and the computer uses this sampled sound to generate the sound of a speaking pipe. So, one might say that the sound font file is the pipes of the MIDITZER. The MIDITZER sound font file has the equivalent of ten ranks of pipes, tuned percussion sounds and untuned percussion such as drums, cymbals and wood blocks. The sound font file used by MIDITZER is furnished with the software and is identified as Miditzer.sf2The two sliders at the top center of the screen track movement of the swell pedals. The sliders correspond two the two swell shoes on a two-chamber organ. When they are positioned at the top, the swell pedal is fully depressed and the swell shades are completely open. When the sliders are at the bottom, the swell pedal is in a closed position and the swell shades are closed. When the swell shades are completely closed MIDITZER continues to produce a low-level sound just as a TPO would do in similar circumstance. If your implementation of MIDITZER only has one swell pedal, both pedal sliders will move in tandem. The slider on the right is the crescendo pedal. When at the bottom or closed position the crescendo pedal is inactive. As the crescendo pedal moves forward additional stops are engaged making the sound produced louder and louder. As the crescendo pedals movement is reversed engaged stops are turned off until eventually all stops activated by the crescendo pedal are no longer engaged. The swell indicators will move as you move the swell pedal on your instrument showing the position of the swell shoe. The crescendo pedal is in the closed position until brought into play. These sliders can be moved with the mouse to vary the sound level as you play on the keyboard.