When a pipe organ vibrantly resounds in a large building, the tone is coming from many diverse sources in many different positions. These positions are three-dimensional, and it is this factor that creates the effect of "spatial dimension". This effect causes the sound to appear to be coming from everywhere at the same time. Consequently, the music floods the whole cubic dimension like a tidal wave.
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When an electronic organ speaks, the tone comes from one or more tone cabinets. The directional effect is quite apparent and produces a "beam effect". This "beam effect" causes the tone to be irregular throughout the auditorium."
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This is all indeed true in synthesized combinations.  A badly amplified synthesized 'full swell' can be absolutely dreadful when compared with a pipe organ delivery.   Nevertheless many 'flue' combinations of electronic design can be enhanced by the number of speakers or a speaker of the Leslie variety which gives a much greater spread of sound to combat the 'beam effect'.   Where the synthesizer triumphs is in the provision of a single timbre, e.g. strings, flute, clarinet & orchestral oboe or a combination of two in a four channel machine, e.g. 8' clarinet and 2^2/3'nazard of the flute variety.   The placing of the amplifier in the centre of the organ chamber allows the solo voice to issue from the same area as the pipe accompaniment.
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If one wishes further dissertation on the voicing of the organ pipe, the website by Colin Pykett provides a wealth of in-depth technicalities.   In his "How the Flue Pipe Speaks", Colin Pykett gives exactly what is required in voicing:-

1. The rate of the tonal build-up and the change of the harmonic structure as the tone  ////matures.
2. The degree of tonal steadiness and the shape of the harmonic structure
3. The rate of decay and the change of the harmonic structure during the decay process.
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Now this is exactly what governs the program in setting a synthesized voice - the attack of the sound (the transient in organ pipes), the sustain, the decay and the release of the note.  This is termed the ADSR graph (attack, decay, sustain, release). What is added, however, is one complete rank/voice adjusted at the consol to take into account the reverberation in the building.   Would that the pipe voicer had this facility to hand in organ building, thereby cutting both time and costs.

The above graph is laid down step by step for each voice singly or in combination.  One can think of the Casio digital synthesizer's programming mechanism as its own inbuilt computer to manufacture the settings.   As I have already stated, these voices should be built in the church and the organist's ear, as in the skills of a tuner, will force the synth to conform to the attack, decay, sustain and release of the organ pipes with the church's acoustics as a secondary factor.    The volume of each program will depend whether it is reproducing a soft positif combination or a solo tuba.   N.B. The volume of the amplifier will remain constant - it is the work of the synth program to determine the necessary volumes.

Below are a number of settings for the Casio range of synthesizers.  We are concerned with the following basic steps in programming the synth.  All of the settings are displayed on an LCD:-

Parameter Section

1. wave forms

.........a) sine wave - pure tone e.g. bourdon, flutes 8' & 4', piccolo 
//////////////////

.........b) triangle wave - suitable for producing diapason ranks
//////////////////

.........c) square wave - suitable for bass clarinet & clarinet sounds
//////////////////

.........d) sawtooth wave - harsher than the above, suitable for orchestral oboe, cornopean, /////////////horn,trumpets, tuba, trombone, bombarde & contra bombarde
//////////////////

2. envelope settings

.........a) DCO  (digital controlled oscillator) using 1 oscillator per voice allows 8 note
.............polyphony i.e. full chords ; 2 oscillators allows only 4 note polyphony - 4 note
             chords.
.........b) DCW (digital controlled waveform) changes the timbre of the sound over time. 
.........c) DCA  (digital controlled amplitude) decides the volume required.

3. vibrato = the organ tremulant and can vary the rate per minute of vibrato and the depth.
4. octave  = similar to the effect of an organ coupler - raises the pitch up or down one
                   octave.
5. detune  = fine-tuning the note e.g. up a octave and a fifth to produce a nazard 2^2/3',
                   although/the synth requires this entry to be 1 octave and 07 notes
                   (i.e.semitones).

^{The following are a few examples of charts with all the settings filled in to enable the user to find a few voices immediately as starters:-} 

^{//Dulciana 8'} 

^{//DCW 1..............................................................................................DCW 2
//Key Follow: 0...................................................................................Key Follow:}

^{//DCA 1............................................................................................DCA 2
//Key Follow: 0................................................................................Key Follow:}

^{//Flute 8' & Tierce 13/5'with tremulant} 

^{//DCW 1.........................................................................................DCW 2
//Key Follow: 0..............................................................................Key Follow: 0}

^{///DCA 1...............................................................................................DCA 2
///Key Follow: 0...................................................................................Key Follow: 0}

^{//Orchestral Oboe 8'}

^{//Tuba Mirabilis 8'} 

Clarinet 8' & Tierce 1^{3/5'
   //}

^{At DCA Step 1, the rate = attack / level = volume
////DCA Step 2, the rate = reverberation}

^{When building a reed voice - 
DCW Step 2, rate - the lower the integer, the more reediness in the attack. 
DCW Step 2, level - the higher the integer the more sustained the reedy edge to the tone.} 

If one wishes no vibrato on a combination which has vib. inbuilt, simply flick the vib. button.

To return to the Casio CZ1000.   An opening was made in the organ console immediately above the Swell manual, the resulting aperture housing the synth keyboard.  The removed panel could be replaced when the keyboard was not in use and fastened in situ by two clips.   A cable ran from the synth up the nearest pillar to the console, along the top of the rood screen and into the North chamber - all very well hidden.   The 200 watt amplifier was positioned in the centre, not the forefront, of the organ chamber and connected to a nearby socket.
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In this way I now had a third manual or, with the quick changing buttons of the synth, really a third and fourth manual.   Pedal sounds could be produced but these had to be played by the left hand duplicated by the organ pedals while the right hand coped with as many notes as was possible.  The use of the pedal tones, therefore, had to be quite selective, e.g. the final line or lines of a hymn.  The occasional chorale prelude, if of sufficiently sparse texture in the manual parts, allowed this also to be a possibility e.g. the chorale prelude "Vom Himmel hoch, da komm' ich her" by Bach.
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Here now are the combinations that emitted from the synthesizer.   I was asked to do a demonstration recital to the local Society of Organists in Tayside and the members had to confess at the end of the evening that they felt that they had been listening entirely to pipework during the demonstration.   One observation - with all pipework blowing, the synthesized Tuba Mirabilis could scythe through the welter of sound like a great well-honed sword!

1. Dulciana 8’
2. Dulciana 8’ + Salicet 4’
3. Small Open Diapason 8
4. Flute 8’ + Nazard 2^2/3’
5. Flutes 8’ + 2’
6. Flute 8’ + Tièrce 1^3/5’
7. Flute 8’ + Septième 1^1/7'
8. Orchestral Oboe 8’