VIRTUAL THEATER ORGAN REGISTRATION BASICS
THE POLYPHONY PROBLEM
With all the wonderful things a modern digital synthesizer can do, it has one serious limitation that sets it apart from the Theater Pipe Organ: THE SYNTHESIZER CAN ONLY PLAY A LIMITED NUMBER OF NOTES AT A TIME. An organist sits down, draws as many stops as desired and plays, giving no thought to how many voices are actually sounding at once. This is no concern in a pipe organ because this instrument has UNLIMITED POLYPHONY, that is, every note that can be played in the instrument is available at once. You could play 'em all if you really wanted to. If you have 10 stops drawn and you play a three note chord, 30 pipes play. play a fourth note, and 40 pipes play. Easy math.
Except for the wind supply, playing a large number of stops at once places no strain on a pipe organ since as was said before, every possible note is instantly available. This is NOT true with the digital synthesizer. Each synthesizer has a certain number of voices that can play at once, referred to as the synth's 'polyphony'. This is usually 32 notes or on larger units, 64 notes. Some 'super size' samplers go even higher. In the example of the pipe organ above, the simple playing of the 3 note chord above would be handled by a synth with 32 note polyphony. Add that 4th note to the chord, and the synth is in trouble. It is not capable of playing all the notes demanded of it. Add to this the fact that every chord is NOT struck perfectly. There may be, intentional or not, 'grace' notes being played as the chord is struck which are either for effect or the result of less than perfect playing technique. In either case, these are additional notes that are required to be played. What happens when a synth runs out of notes? It varies by the equipment, and in some cases can actually be programmed into the units, but most often the note having been played the longest drops out first. The result is that you hear the latest thing played, but your background harmonies may drop out. Needless to say, you do not want what is being played to be at the mercy of some fool machine! A number of steps must be taken in the registration of a Virtual Theater Organ to insure that polyphony is conserved.
The best practical way to emulate a Theater Pipe Organ is to do it stop-by-stop, with each individual stop represented by a synthesizer program, and combine the stops in synth combinations (or patches) which represent a given registration. In setting up these combinations, individual ranks can be assigned tunings, trem speeds, and all the other randomness that makes a Theater Organ such a massive sounding instrument. The main goal in Virtual Theater Organ registration is to create these combinations representing Theater Organ registrations using as few synthesizer voices as possible. This is referred to as conserving polyphony. Here are some of the ways in which polyphony can be conserved:
Add More Synths-Two Or More Per Manual
On my Great manual, it was determined long ago that since this is whe manual where the large ensemble registrations would be played, as much polyphony as possible would be needed. Two Korg 01 synths are used in tandem on this manual. They BOTH are set to global channel=2 which means that they play simultaneously then channel 2 signals from the great manual are received. They also both respond to MIDI program change when a change is sent on channel 2. Each synth contains half the stops that make up a given registration. The 'programs' inside the two synths are identical. Program changes control synth combinations which contain up to 8 of these programs per synth, so a maximum of 16 programs for the Great. As a practical matter, only about 5 programs per synth can be used without dropouts. Still, if you follow the registration techniques here, this can be an awfully full sounding ensemble.
Create Celestes using Chorus Effects
I'm sure this one is going to raise some eyebrows. In massive effects such as 16' 8' 4' String and Vox choruses, Independent detuned Celeste ranks at several pitches along with the straight tuned ranks can make the polyphony add up fast. Besides, with the ATRISTIC application of the proper chorusing effects, the celeste achieved through chorusing is more pleasant, fuller, and more massed sounding than two oscillators a few cents out of tune with each other. The chorus can also be a more accurate representation of celeste tuning because the amount of de-tuning is SCALED along the compass of the stop as it it in a skillfully tuned set of celeste pipes. Although one set of String ranks through a chorus effect may not be enough in the largest registrations, Two at most, a sharply voiced rank and a more full bodied rank slightly detuned to each other might be all that is needed.
Make Every Stop Count-Determine the Essence of the Registration
If the basis if a planned registration is, for instance, 8' String, 8' Vox, 4' Tibia, There is certainly no need to haul out every 'filler' stop in the organ to 'flesh out' this registration. If your Voxes and Strings are voiced fully enough and the String has a chorused celeste (all Theater Organ strings should have a celeste), this should carry the essence of the registration through.
In reading some books and articles on Theater Organ Registration, the authors make recommendations of adding a multitude of 'filler' and 'binder' stops in ensemble registrations. This is perfectly fine in pipe organs and some high-end electronics where the number of notes being being played at once is of no matter. Unfortunately this is not the case for the Virtual Theater organ with the polyphony limitations it inherits from the digital synthesizers that power it. The pages in this site on registration, and especially ensemble registration, show you techniques to get the big ensemble sound without banks of synths. The Great Manual of my own organ is capable of very full registration, yet has only two dedicated 32 voice synthesizers allocated to it. The Virtual Theater organ has its admitted limitations in the area of ensemble registration, but with clever use of its resources, these limitations can be overcome.
Use Inter-Manual Couplers
In addition to the two Korg 01 synths that are dedicated to my Great Manual, I have wired in Solo to Great couplers at 16' 8' and 4'. The Solo is powered by an Akai S2000 sampler with 32 note polyphony. 'Piggybacked' onto the Akai for use on the Solo is a Korg X5DR with an additional 64 notes of polyphony. If I were to couple the Solo to the Great at just one pitch, I would have the potential for 160 voices! The one disadvantage to such a system is that you tie up two manuals to get one sound. An advantage to coupling in an additional manual powered by another synth is that the more independent synths that are used, the less chance there is for phase locking. The less phase locking there is, the more massed the sound.
Utilize Random Tuning Options
If your synths have a 'random tuning' option available whereby tuning within the instrument and between voices can intentionally drift, by all means use it. I was introduced to that by Mr. Nelson Clark who with other organ hobbyiests has been using random tuning on Korg based Virtual Theater Organs. The effect is very noticable especially in large ensembles. Every so often with deliberate detuning within the various voices PLUS the random tuning effects, a little bit of a 'clinker' occurrs. I love it, it's part of the realism of the Virtual Theater Organ. For that matter, every once in a long while a MIDI glitch will actually produce a cipher. That may be taking realism a little too far, folks!
For more information on
Virtual Theater Organ Registration Basics-Families of Theater Organ Tone
Virtual Theater Organ Registration Basics-The Tibia/String Relationships
Virtual Theater Organ Registration Basics-Esemble Registrations
Virtual Theater Organ Registration Basics-The Polphony Problem