HB3, a Digital Organ System by The Organ Workshop
HB3 is The Organ Workshop’s new digital pipe-organ simulator, intended to reproduce the full sound of the dozens of pipe ranks that play together in any typical wind-driven pipe organ.
In continuous development since mid-2017, HB3 uses no pre-recorded sound samples, preferring to synthesize the individual complex evolving sound of each pipe in real-time. This approach overcomes all of the inevitable limitations & side-effects associated with sampling systems that re-play and loop-around existing digital recordings, and enables precise control over the tonal voicing and scaling within every rank.
The system also features a unique frequency-regulation mechanism, whereby any frequency resonances produced by loudspeaker or by building acoustics are effectively eliminated from each note's makeup before their sound reaches the amplifiers & loudspeakers.
HB3 runs on standard off-the-shelf PC hardware. Multi-channel audio is provided by incorporating a regular studio audio interface, and every part of the system is controlled by MIDI. The combination of USB-MIDI and an ASIO Audio Interface provides a fast playing response and extremely low audio latency.
The HB3 system has now been developed to the point where it can serve as the internal sound generator for a fully equipped large organ console, or can be built as a smaller-scale generator unit, for example for adding digital ranks to an existing pipe organ. In both these cases the PC unit that hosts HB3 runs unattended and hidden inside the case, without the need for a monitor or mouse.
During the period a new organ is being set up, however, the system provides various visual tools, as illustrated below :
Above is a screenshot of a typical HB3 department, in this particular case for a 13 speaking-stop Swell organ division. (13 stops, but in reality 17 ranks are employed here in total, because a group of 5 independent ranks, operated together, make up the Swell Mixture V stop).
The example above is the equivalent of a typical enclosed manual division within a pipe organ, incorporating swell-box shutters and a tremulant. At the top of the graphical display illustrated above are all the general department settings for these, plus wind-demand, fine-tuning, temperament, and various controls for overall audio level and tonal correction. Many of these functions can be remotely controlled by MIDI from the organ console.
Beneath them are the 17 ranks in the department, and within each rank a number of individual local settings are provided for setting up and balancing everything, such as the rank's MIDI switch number, rank volume, stereo layout & width and audio channel distribution.
Important to note that each of the 5 ranks that comprise the Swell Mixture V stop here are generated and voiced entirely separately, just as they are in a pipe organ stop of that name, where you'd find 5 complete rows of 61 pipes, 305 in total. This full-scale arrangement has in the past rarely been properly catered for in commercial digital organs or sampled-organ systems, which have commonly relied on composite Mixture sounds or sampled recordings. Indeed in the HB3 system every single 'digital pipe' is always generated independently, each one with its own unique voiced parameters.
A complete organ system would contain several such departments, at least one for each manual. Although an HB3 department such as illustrated may contain any number of ranks, it is in practice often more convenient & flexible for a manual to be split into two or more smaller departments, named, for example, Swell 1, Swell 2 etc.
In every rank a number of controls are provided for general set up & balancing, but for more detailed voicing of any rank clicking on the green ‘V’ button at its left-hand end brings up the Voicer screen, which immediately loads up the data from the rank you've selected :
Rank Parameter Voicing
The HB3 Voicer provides access to all of the detailed parameters that define the behaviour of each rank's digital generators. It is arranged to control the 4 parallel generator sections that create each sound, referred to as A, B, C and Air. Each have their own voicing screen; the section A generator sceen in the Voicer is illustrated above.
A, B & C generators :
Although superficially similar A, B & C are designed to have various unique functions such as are required by ‘sustain’, ‘transient’, ‘modulation’ etc, but to a large degree the entire setup can be tailored to the different requirements of the various pipe families - Flute, String, Diapason and Reed.
Standout sections in the Voicer illustrated here are firstly the 6 keyboard 'Voicing Points’, featuring adjustable harmonic bar-graphs. Secondly, the envelope section over on the right is where the note-scaled timings and shapes of attack & release and various transient settings are set up. There are various envelopes for different elements of a note’s amplitude and for its dynamic pitch.
The Voicing Point graphs set the rank’s exact harmonic structures at each of the six C keys on an organ keyboard; similar sets of 6 graphs feature in each of the A, B & C sections. For the 11 notes in between each of the C voicing-point notes - C#, D, D#, E, F etc. - harmonic values are automatically computed by interpolation between the two adjacent voicing points, such that a precise and completely smooth tonal keyboard scaling may be achieved. As a result, every note in an HB3 rank is unique and independent, as is the case with pipes.
In the ‘AIR’ section, dynamically-contoured pipe air-noise parameters are inserted at each voicing point, for adding a realistic evolving modulation to the transient and sustain sounds. And again, (as with all elements within HB3) the parameters & proportions for each keyboard note in the rank are smoothly interpolated individually between the 6 voicing points.
A vast range of pipe air-sounds can be created in the AIR section. The cut-off, scaling and resonance controls provide access to a wide variety of open-pipe or stopped-pipe characteristics, and these sounds are then combined and/or modulated with the waveforms created by the A, B & C sections.
Pitch controls :
The Rank's basic pitch (32', 8', 4', 1 3/5' etc. etc.) is selected in the section above Envelopes. Also available here, for ranks that require it, is celeste-tuning (sharp or flat), where the degrees of off-tuning at each end of the keyboard are inedependantly settable for a Celeste stop. Finally for Mixture ranks, 'Break-Back' allows notes to fold back to a lower pitch at any selectable keyboard note position.
Voice Library :
A large library of pre-assembled voices has been developed to date, and they are available for immediate loading into any rank in any department by selecting 'Load from Library' from within the Voicer. Existing library voices can then be edited & refined and the library added to as required, either during configuration or when actually voicing a completed instrument. There is no limit to the number of voices that can be created and stored in an HB3 library.
A uniqe & powerful feature of the HB3 system, Regulation provides precision adjustment and correction of the sonic irregularities that invariably occur in any room due to loudspeaker and acoustic resonances. Rather than merely altering the power of individual notes, it addresses the frequency spectrum itself.
On occasion these irregularities can be surprisingly severe (particularly towards the bass), where an individual note-frequency can often be found to be much, much louder, or quieter, than its two adjacent neighbours.
Because HB3 creates its note-waveforms by assembling chains of harmonics, it has become practical to completely cancel such irregularities by automatically modifying the makeup of the actual source waveforms from which each of the individual pipes’ tones are assembled. In effect, the harmonic composition of each note (every 'pipe') is automatically modified by HB3 Regulation to compensate for the surrounding acoustics.
[Frequency regulation in a recognisably similar form was actually a feature of many of the very early analogue electronic organs - such as those made by the Hammond or Compton organ companies - but has never hitherto been practical on any digital system. The majority of digital organ manufacturers nowadays attempt to tackle the regulation issue by merely providing loudness & tonal adjustments for each note].
The Regulator is played from a keyboard - either one of the organ's own manuals or using a remote MIDI keyboard. The operator hears pure semitone sine-waves from the loudspeakers, a complete frequency range from around 15Hz to 18kHz, more than 10 octaves. The loudness of each of the tones is then individually adjusted by ear until a satisfactorily smooth response is achieved throughout the compass.
The result of this process is then saved as a Regulation table. There may be just one Regulation required by an organ system, or within a larger multi-channel installation specific Regulations are created & saved for each loudspeaker set.
Then, whenever HB3 starts up, the appropriate Regulation table is referenced during the note-waveform creation process, and this adjusts the precise level of each harmonic as the system proceeds up the scale to create each one of the thousands of waves. In practice this entire wave-writing process takes only a second or so, even for a large organ.
Some unique details are constantly being added during the development of HB3. For example the system can now be totally touch-sensitive, such that it responds to MIDI-Velocity-equipped keyboards in much the same way as direct mechanical pipe action. This means the player can control the virtual pallet movement - both when pressing and releasing the keys - and hence affect the resulting nuances of pipe speech.
Digital wind reservoirs form a central part of the way the digital-pipes play, and the adjustable wind-demand feature is able to reproduce the typical ‘bounce & oscillation’ of a real-life bellows system.
Another HB3 first - ‘Pitch Hunting’ simulates the way that pipes interfere with each other’s tuning. The phenomenon is easy to demonstrate when two pipes are being tuned together, but in practice this is something that progresses continuously - in real life pipes push & pull each other’s tuned pitches as music is performed. Pipes playing the same note, or a harmonically related note, have a constant inclination to lock-step with their neighbours, but then in the next instant another harmonic pairing might take precedence, shifting all the internal tunings slightly. Pitch Hunting in HB3 endeavours to replicate this continuous internal tuning interference.
Because the HB3 system has a natural capability to create truly linear even-scaling within every rank, a degree of more life-like variation is offered by an individual rank's ‘Irregularity’ adjustment, causing specific notes’ characteristics to vary within chosen limits.
Opening or shutting a Swell Box has several effects on the sound of the pipes inside. As the box is closed, in parallel with an overall volume reduction the tone becomes more muffled, as one would expect. But moreover inside a shut swell box the effects of pitch-hunting are exacerbated, both because of the general air pressure build up inside the box and because of increased internal acoustic reflections. This feature too is available as an adjustment within the pitch-hunting algorithm.
The HB3 System has been designed to provide comprehensive sound generation within regular solenoid-drawstop, solenoid-tab or illuminated-tab consoles, but as an alternative it can be configured entirely for touch-screen monitor control, complete with couplers, on-screen pistons, reversers and memories.
A touch-screen example we implemented recently is illustrated below :
Full Piston Action & Couplers and hardware switch inputs & outputs have recently been added to the capabilities of HB3, including solenoid pulse driving of drawstops, so The Organ Workshop can now provide all the requirements of a complete digital organ within a single system.
Hugh Banton December 2022