A simulation of the St Albans WurliTzer
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  A digital simulation of the 1933 WurliTzer organ at the St Albans organ museum  


Colin Pykett


Posted: 20 November 2021
Revised: 9 December 2021
Copyright C E Pykett


(click on the headings below to access the desired section)



The Wurlitzer pipe organ

The organ as simulated:

    Playing interface
    Stop list

What does it sound like?


Notes and references





In 1933 a three manual ten rank Wurlitzer theatre pipe organ (style 220SP; opus 2183) was installed in the Empire (later the Granada) cinema at Edmonton, north of London [1]. The cinema closed in 1968 and it was therefore fortunate that in the following year the organ was acquired by the St Albans organ museum and theatre [2], restored and then brought into use by a team led by Fred Jennings. Around that time I had for many years been well acquainted with the late Bill Walker, who formerly chaired the board of Trustees of the theatre among his other interests and activities until his untimely death in 2003. These interests included his positions as CEO both of the Livingston Organ brand of electronic instruments and the Organ Supplies and Services company. So I was grateful to the Trustees for permission to digitally sample the Wurlitzer with the intention of developing a sample set for use in the Prog Organ virtual pipe organ [6], and this forms the subject of this article. On the same occasion I sampled the Rutt theatre pipe organ also in the care of the St Albans theatre. This is now an extremely rare instrument, and a companion article describing it is available on this site [8].



The Wurlitzer pipe organ




Figure 1. The Wurlitzer console at the organ theatre, St Albans, England


The Wurlitzer console is pictured in Figure 1 and the organ's innards are distributed across three chambers. Unusually, this enables the percussions (apart from the piano) to occupy their own chamber and be under separate expression. Today the piano is a splendid instrument in its own right, a Weber duo-art grand, though it was not part of the original organ installation.


 Diaphonic Diapason  97
 Tibia 97
 Flute 97
 String 85
 Celeste 49
 Vox Humana 73
 Brass Trumpet 61
 Tuba 85
 Clarinet 61
 Orchestral Oboe 61




Table 1. The pipe ranks of the Wurlitzer


The ten pipe ranks of the organ are listed in Table 1. It is assumed that readers are familiar with the concept of the fully unified organ as used in theatre instruments. Suffice to say that each pipe can, in theory, be played from any key on any manual of the console, including the second touch contacts. Thus the Tibia, for example, is an 8-octave rank which appears on all divisions at various speaking pitches ranging from 16 foot to 2 foot (see the full specification of the organ at reference [1]).


The pipes, percussions and effects within the chambers of the original instrument can be thought of as a stand-alone core resource of sounds which can be drawn on in any number of different ways by a console having a wide variety of possible stop lists. The console and the chambers are separated by what is called the 'relay' which maps the one into the other, this far-sighted and elegant unification architecture having been invented by Robert Hope-Jones in the 1880s. Originally the relay in these instruments was a huge electropneumatic affair occupying its own room, though nowadays it is often implemented electronically with computer control when organs are rebuilt. Consequently the specification chosen by Wurlitzer's in this case was only one option out of many feasible alternatives. This is quite different to a traditional organ built strictly along 'straight' lines, where each pipe rank corresponds to one, and only one, speaking stop at the console and there is therefore no need for a relay.



The organ as simulated


The simulated organ was designed in the same way as the pipe organ. It consists of a core sound engine set up in a desktop computer containing the same ten ranks of sound samples as the pipe organ, together with a range of tonal percussions and traps (non-tonal percussions). Prog Organ sees to the relay function in this case since it has a level of note and stop switching sitting between the console and the sound engine itself, implemented in software. None of the Wurlitzer effects such as birds, horses hooves and fire gongs were included though, since the light music I play seldom calls for them and I did not want to tie up stop keys on the console with things which would not be used. However three additional simulated pipe ranks were incorporated - a second ('mellow') String, a Krumet and a Kinura. The latter two are quiet but penetrating fizzy reed ranks which can be useful in jazzing up a number - Hope-Jones again - although some unkind people liken their sounds to comb and paper! The resulting 'sound core' of the simulated instrument is shown in Table 2.





 Diaphonic Diapason 85     Tuba 73  Piano (with sustain pedal)   Cymbal Tap
 Flute 85  String 73  Glockenspiel  Crash Cymbal 
 Mellow String (note 1)  85  Tibia 96  Chrysoglott  Brush Snare
 String Celeste 49  Vox Humana 61  Chimes  Wood Block
 Krumet (note 1) 61  Brass Trumpet 61
 Orchestral Oboe 61
 Kinura (note 1) 61
 Clarinet 61


Table 2. The 'core' virtual Wurlitzer theatre pipe organ sound engine



1. These three ranks are additional to those of the original Wurlitzer organ.
2. Individual software-adjustable tremulants are available for the notes within all ranks.
3. Each note of each rank plays in stereo with software-adjustable panning.
4. Up to six independent sound channels plus three derived sub-woofer channels.
5. 10 channels of external convolution reverberation (hardware).
6. External graphic EQs (hardware).
7. Two swell pedals to the Main and Solo chambers.
8. Piano sustain pedal (foot switch to the right of the swell pedals).

Some of the notes above will bear amplification, as follows:


With all sound samplers, including Prog Organ, you are pretty much stuck with the sound of each recorded sample in the same way that you are stuck with the sound of a symphony orchestra recorded on a CD. In other words, the options for voicing individual samples are limited. They cannot be voiced in anything approaching the way that organ pipes can when a skilled voicer undertakes the tonal finishing of a real instrument. S/he can adjust the attack and decay characteristics of individual pipes, and particularly their steady-state tone colours, within wide limits. There are those who argue that this major drawback does not matter, though it is noteworthy that they tend to have vested interests in selling or promoting a particular brand of sampled sound organ. But of course it matters. Whoever heard of a real organ whose pipes cannot be voiced! And why should an organ builder (me in this case) be denied, purely through technology limitations, the opportunity to voice an instrument realistically? Unfortunately though, one just has to put up with the situation by balancing it against the undoubted advantages of sampled sounds. To get round the problem one would need to move to a synthetic sound generation system such as physical modelling, additive synthesis or (a technique I invented) trendline synthesis [3]. However these also have their own pros and cons. But as in life generally, half a loaf is better than none, and the Prog Organ sound engine offers several options for adjusting the sound of each sample in lesser ways. Some of these are listed in the notes above and they include adjustable stereo pan between a pair of loudspeakers, EQ (tone control) and volume. But all current digital simulation methods are imperfect, and it reveals something about those who maintain that they are not.


The notes above also mention that Prog Organ can add an adjustable tremulant to each sample, not just to each stop or rank, and this brings us to another important topic. Few would disagree that its multiple tremulants are one of the glories of the theatre organ, yet here again we meet head-on another shortcoming of sampled sound synthesis. I have spent years trying to solve the problems of simulating tremulants successfully. To be brief, the difficulties of denoising and looping tremulated samples are writ large, since these are bad enough for untremulated sounds. But having done it, one can then accommodate in the sound engine a duplicate set of tremulated samples, even though this is grossly inefficient from several points of view. But to my mind the worst problems with the duplicated approach are twofold: the tremulants cannot be adjusted, and the relative phase of a tremulant becomes randomised across a rank when several notes are keyed at once, whereas it beats in phase for all the pipes in a real organ fed from the same tremulated wind line.  This occurs because tremulant phase is defined for all pipes by the tremulant itself in a pipe organ, whereas with tremulated samples each one has a different phase depending on when it was keyed. This can make this type of simulated tremulant sound rather unrealistic and sometimes positively unsatisfactory. Instead of a clear beat or giggle, the tremulant becomes ill-defined and foggy especially when chords are played. In contrast, Prog Organ's tremulants are parametric, meaning that the sound engine applies a low frequency periodic variation to certain parameters of each sample such as its frequency and amplitude. More subtle variations are also possible, such as changing the timbre of a sample over each tremulant cycle. This is done by passing the sample through a filter whose parameters are controlled in real time by the instantaneous amplitude of the tremulant oscillator. Although I would not claim that the Prog Organ tremulants are perfect in every particular, at least they are adjustable over a wide range, and they do not suffer from the random phase problem. A lengthy article is available elsewhere on this website which discusses the tremulant issue in detail [4].


Another important aspect of tremulants is their intimate association with the ambience of the auditorium. This relationship is so close that the effect of an otherwise good tremulant can vanish altogether in completely anechoic conditions! This can astonish those who have not come across it before. An article elsewhere on this site discusses the effect and contains some sound clips which demonstrate it [5]. The UK cinemas in which theatre pipe organs were installed were frequently badly designed acoustically since they were often repurposed silent movie picture palaces where the acoustics were obviously of little account, or former Victorian or Edwardian music halls (this was true of the Empire cinema in which this Wurlitzer was originally installed). So their acoustics were generally not well controlled and quite often far from dry. Even if an auditorium does sound dry in the sense of having a short reverberation time, it will always be non-anechoic because its boxy shape with several pairs of long parallel boundaries still results in enough reflections to add significant colouration to the sound in the form of room modes. The upshot was that theatre pipe organ builders had to match the subjective effects of their tremulants to an often unsatisfactory building, unconsciously or otherwise, which is one reason why some of them seem inadequate (too violent or reticent) when transferred elsewhere. Even tremulants need to be 'voiced' on site!


As a consequence of all this, Prog Organ uses convolution reverberation to add room ambience to the sounds of this simulated Wurlitzer rather than trying slavishly to emulate the vestigial wetness of the St Albans organ theatre itself. Not only is this venue not the organ's original home, but attempting to reproduce realistically the reverb tails of wet tremulated samples is difficult in any case [7]. Up to ten channels of reverberation are available from five external hardware units. Each one handles a stereo pair, and even if presented with a mono input signal it will generate a stereo output from the convolver in the same way that a real room does. Therefore a wide range of room ambience can be simulated depending on how the reverb processors are patched between the outputs of Prog Organ and its several loudspeaker channels, together with the settings chosen for each one. But the main point to take away here is that reverberation can add dramatically to the effect of tremulants if chosen with discretion.


Unless instructed otherwise, Prog Organ does not allow any sound sample (simulated pipe) to speak more than once at any moment. This is because a pipe in a real theatre pipe organ can itself only speak once - obviously - regardless of how many simultaneous demands are made on it by the relay. It is a simple programming matter to incorporate this feature, so it is surprising that it apparently eludes some sampled sound organs. Of course, it means that there are missing notes when the simulated organ is played, just as there are missing notes in any pipe organ which uses extended and duplexed ranks. But that's life. Simulating unification properly also has the advantage that the polyphony demand on the sound engine of a unified digital organ is far less than that for a straight organ with the same stop list, and this can sometimes be beneficial. For instance, it would be possible to simulate effectively a large unified organ such as this Wurlitzer using RPi or Arduino technology because of the relatively small memory footprint and polyphony requirement of the core sound engine owing to the relatively small number of pipes.


Playing interface
As with most VPOs, the simulated organ can be played in two ways. One can simply fire pre-prepared MIDI files into it and then just sit back and listen to the results, much as a fairground organ plays from punched cardboard music books. Since the sound-producing elements of the real Wurlitzer are represented within the sound engine as sampled sounds, this would produce a very convincing imitation of the real thing. The second approach is to connect an actual organ console to the sound engine so that the organ can be played in real time by a human performer. Since I am one of these, I prefer this latter method.



Figure 2. The Prog Organ virtual pipe organ console used during sample set development


In theory, it would be quite possible to drive the sound engine from the actual Wurlitzer console at St Albans, given a suitable hardware playing interface (either using MIDI or the contact scanning feature of Prog Organ [6]). In practice, the Prog Organ console which I use for developing sample sets (Figure 2) is a far cry from the splendid article pictured earlier (Figure 1), being limited to two manuals with no second touch and only 46 stop keys. However the stop keys are motorised, there is a combination capture system, two swell pedals and a foot switch which currently functions as the piano sustain pedal. So by straight organ norms it is a reasonably well equipped console for a large two manual instrument, much better than the collection of plastic MIDI controller keyboards balanced on the piles of books to be found among the ranks of VPO enthusiasts! And one should not forget that the number of pipes in the Wurlitzer at St Albans is about the same as that of a small straight organ with only twelve speaking stops on the manuals and one on the pedals. So in practice it is not difficult to coax quite a lot from this console, and it is capable of rendering much of the staple repertoire of the theatre organ. One very good player, a well known theatre organist, remarked to the audience at a public demonstration that "I've never heard electronic tibias this good", and he was well acquainted with the real Wurlitzer at St Albans. Of course, what he was hearing WERE the Wurlitzer tibias, or at least recorded versions of them.


Stop list
The current stop list of the instrument is shown in Table 3, though any number of variations would be possible without modifying the core sound engine itself. This is one of the attractive features of simulating a unified organ - you can set up any stop list you like without having to delve into the sound engine. In effect, you would be merely modifying the 'wiring' of the relay. In the case of Prog Organ it means that you would have to write a different Configuration File, equivalent to the Organ Definition Files of some other VPOs.


    ACCOMPANIMENT                 SOLO


      PEDAL               OTHER
 Diapason   8       Tuba Profunda   16    Tuba Profunda   16   Main Tremulants 
 Concert Flute 8  Tibia Bass 16  Diaphonic Diapason  16  Solo Tremulants
 Mellow String 8  Contra Viol 16  Mellow String Bass 16
 String Celeste 8  Vox Humana 16  Tibia 16  Crash Cymbal
 Krumet 8  Brass Trumpet   8  Mellow String Octave    8  Triangle
 Kinura 8  Harmonic Tuba   8  Tibia Octave   8  Wood Block
 Clarinet 8  Tibia   8  
 Vox Humana 8  Violin   8  Accompt to Pedal
 Diapason Octave 4  Vox Humana   8  Solo to Pedal
 Flute 4  Orchestral Oboe   8
 Mellow String Octave 4  Tibia Octave   4
 Flute Piccolo 2  Viol   4
 Tibia Twelfth 2 2/3
 Tibia Piccolo  2
 Piano  Piano
 Chrysoglott  Chrysoglott

Table 3. Stop list of the simulated instrument


The stop names and some of the chorus work in this specification are loosely based on those of the real Wurlitzer, and the two swell pedals control the ranks and percussions in the Main and Solo virtual chambers shown earlier in Table 2. In this reduced specification the Accompaniment division is based around the silvery Flute rank rather than the Tibias, though it can be filled out with the Diapasons to balance the fuller-sounding Tibias on the Solo if necessary. Both divisions have a generous helping of string and reed tone, especially as three additional ranks have been included. So the organ is not short on tone colour compared with a typical two manual instrument of maybe six ranks. Although there are only two tremulant stop keys, they control all of the independent tremulants for each rank in their associated 'chamber' whose parameters can be adjusted within wide limits as mentioned earlier.



What does it sound like?


Hopefully the recordings below will give some idea of what the simulation sounds like. As much of the best light music in the theatre organ repertoire is still in copyright, one has to fall back on the lighter classical or Victorian/Edwardian music hall genres, which rather restricts the options here. But it goes without saying that if you really want to hear what this wonderful instrument from yesteryear is capable of, then you should visit the St Albans organ theatre itself. Those who work so hard to keep organs like this one in such fine condition deserve our support.


The numbers here demonstrate the sounds of the instrument both with and without tremulants:

  Since the day I met you (Harry Dacre) - 2.45 MB/2m 40s

  Holsworthy Church Bells (S S Wesley arr. Pykett) - 3.45 MB/3m 46s




Many thanks go to the St Albans organ theatre for permission to sample this fine organ.




Notes and references


1. National Pipe Organ Register - index number A00545

    https://www.npor.org.uk/NPORView.html?RI=A00545  (accessed 20 November 2021)

2. https://stalbansorgantheatre.org.uk/  (accessed 20 November 2021)

3. 'Trendline synthesis - a new music synthesis technique', an article on this website, C E Pykett 2016.

4. 'Tremulant simulation in digital organs', an article on this website, C E Pykett 2009.

5. 'The interaction of tremulants with room acoustics', an article on this website, C E Pykett 2009.

6. 'Prog Organ - a virtual pipe organ', an article on this website, C E Pykett.

7. When reproducing wet samples it is necessary to match the instantaneous phases and amplitudes of both the audio signal and the tremulant at key release to those at the beginning of the reverb tail if there is to be no audible discontinuity. This is difficult enough for untremulated samples, let alone for tremulated ones. For a detailed discussion see:

    'Wet or dry sampling for digital organs?', an article on this website, C E Pykett 2010.


8. 'A digital simulation of the Rutt theatre organ at the St Albans organ theatre', an article on this website, C E Pykett 2021