Divide

Video Demo

A custom oscillator for logue-sdk compatible synthesizers that lets you bring back some of the great (and some maybe not so great) sounds of the "Divider" era of organs and synthesizers.

As always, these are to be used at your own risk!

A quick word...

I've been having a ton of fun creating these plugins, and your support really helps! If you like stuff like this and my other work, by all means feel free to contribute whatever you can to help support this!

Ensure you have the KORG minilogue/prologue sound librarian installed. Now, before you do anything else, perform a full and complete backup of your synthesizer and save this to disk before continuing. See the sound librarian manual for instructions on how to do this if required. Next, select the USER OSCILLATORS tab on the librarian, and drag and drop the requisite file to an available slot in the librarian :

  • for minilogue xd users, please use divide.mnlgxdunit
  • for prologue users, please use divide.prlgunit.
  • For the NTS-1, you can certainly use the prologue file... "Generally"... this is aimed at polyphonic usage with the xd or the prologues, however far be it from me to tell you what to do!

Divide Down Synthesis

Ahh, divider organs, and synthesizers. The origin of "synthesizer polyphony", but often derided for sometimes having a 'thin', or 'static' sound despite providing true "full" polyphony across the entire keyboard range. These organs / synthesizers use a fixed oscillator for a high note, and then use simple divide-by-two flip-flops to get subsequent lower octaves. The upshot of this vs multiple individual oscillators, is that the divider circuit is not only simpler - and cheaper, it doesn't require tuning and is thus more stable overall. The downside of this, is that the divided tones will always be perfectly in tune - and in phase, with their respective top octave. This however can be utilized to advange to get more unique waveforms if desired as we'll explore later.

Divide Down Synthesis Types

For the top most octave to be generated, divider synthesis generally approaches this using two basic methods, each with their own advantages and disadvantages :

  • Single Top Octave Generator IC Often found in cheaper 'home' organs, string machines (and even the Moog / Realistic MG-1, and Polymoog), these start with a single master oscillator (about 2mhz) running into a single IC that divides this clock by varying integer amounts (/239 for C, /253 for B, /268 for A# etc). This does mean however that everything is tied to a single master clock, and everything (not just the octaves) is phase-locked to each other, which most certainly can yield the 'static' thin sound often attributed to these organs and synthesizers.

    These generally do not require tuning as the master oscillator can be crystal controlled, however if they do, they only require only one oscillator to be calibrated / tuned.
    This type of sound, if desired can be emulated by this user oscillator.

    Adding a second top octave generator / divider set can certainly thicken up the sound much like having a 2 VCO synth vs a single VCO, however this doubles the required circuitry (and cost). The Moog Polymoog is one example...

  • 12 Unique Top Octave Generators This form of divide down synthesis relies on 12 individual unique oscillators providing the uppermost pitch required for the 12 notes. These are still divided down in half for each subsequent octave, however now we have 12 unique sources of pitch for the 12 notes. Aside from providing the possibility to support alternate tunings from equal temperament, this more importantly provides 12 unique and free-running sources of pitch for each note. Thus, chords tend to sound more 'organic' and warm vs their single master oscillator counterparts. And, more importantly, any notes played that use non-octave drawbars / mixtures, will source their sound from a different oscillator, thus yielding a less 'static' timbre to the overall sound.

    This has an additional advantage with vibrato: With a single common top octave source, applying the vibrato to this single master oscillator means the sound will vary in pitch perfectly in unison, which certainly adds to the overall 'static' nature of the sound. However, when we have 12 free-running top octave generators and we apply a single vibrato LFO to this, while yes, each note will vary with the LFO at the same phase / frequency, each top octave oscillator will not quite vary at the same amount. This becomes especially important when playing chords or using mixture drawbars - it again adds some more motion and adds to an overall more 'organic' sound.
    This type of synthesis is also emulated by this user oscillator, as well as this type of vibrato.

  • Not all organs used divide down topologies! A few years ago I had an old Conn 640 organ that actually used a unique oscillator for each tone to be generated - 72 of them. This meant there were 72 oscillators (36 tubes) that each required tuning - with a wrench or a socket to a coil no less. That said, it did lend a warmer / more natural sound vs a divider. This is obviously much more complex than a divide-down architecture, and is not emulated with this oscillator.

Not Just Squares

Just because we are dividing down by 2 does not necessarily mean we're restricted to just a simple square wave synthesizer (although some cheaper models were). A few tricks were sometimes applied to get various waveforms out of these:

  • Additive synthesis : Adding squares together in octaves at subsequently half amplitudes could generate a staircase sawtooth - for example (C0 * 1) + (C1 * 1/2) + (C2 * 1/4) + (C2 * 1/8)

  • Voicing circuits per note : Despite the divider generally producing a square wave, these are often passed into a voicing circuit per note output, however this can result in unique capacitor / resistor values per note as well, adding complexity / cost etc

  • Logical Operations : Divide-by-two flip-flops generally output a square wave - why not feed these into logic gates for more waveforms? Sure - feed two octaves into an AND gate, and you get a 25% pulse wave.

  • Voicing Filters / 'wah' effects etc : Once the overall tone was generated and mixed from the relatively bright / harsh divider outputs, this signal was then fed into a common voicing / shaping filter, somtimes with an auto-wah effect added for fun too.

Effects

To add some variation, and 'fun' to the overall experience, many of these organs added some 'special effects', such as pitch benders, arpeggiators, repeaters, envelopes, and tremolos - many of which are supported both by the existing architechture of your synthesizer, and by this oscillator, listed in detail below.

Usage

The following parameters are given to the user to adjust the sound of this oscillator :

Shape:

Smoothly rolls through 7 different preset drawbar settings:

This oscillator fundamentally generates it's sound internally via 4 drawbars. These are:

  • 16': This is 1 octave lower than the note you are playing.
  • 8': This is the same octave that the note you are playing.
  • 4': This is 1 octave above the note that you are playing.
  • IV: This is a "Mixture" drawbar, as explained below.

This "IV" Mixture drawbar singly will mix 4 separate pitches (footages) to generate a unique complex tone, as follows:

  • 2' (+2 octaves)
  • 1' (+3 octaves
  • 223' (a "g" played an octave above the note you're playing)
  • 135' (an "e" played two octaves above the note you're playing)

So, we would require 4 unique parameters to be able to freely adjust these individual drawbar levels. However, this would use up 4 out of the 6 available parameter slots! And some drawbar combinations effectively yield the same timbre - just the 16', 8' or 4' drawbar out alone gives you the same sound just at varying octaves, etc.

So a simple solution to this was to turn the shape knob into a single drawknob. This smoothly cycles through these 7 presets (generally getting "brighter" the more you turn up the SHAPE knob: Drawbar levels are rated from 0 to 8, where 0 = no sound and 8 = a full level

  • 0800 : Just the 8' (root) drawbar
  • 8800 : 8' + 16' drawbars.
  • 8000 : Just the 16' (sub fundamental) drawbar
  • 8611 : A slightly darker sound
  • 8880 : 16'+8'+4' - all root drawbars
  • 8008 : 16' subfundamental + the mixture drawbar
  • 8888 : Full organ - all stops out

As we smoothly sweep between these presets, we can achieve various combinations between these presets. Want a "4800" sound? Set the shape knob to around 7%, etc...
By applying the LFO to SHAPE, we can smoothly cycle through these presets for an 'evolving' sound, useful for pads and other sounds (see the video demo for some examples).

Note, the overall amplitude through the shape knob range is normalized to keep the amplitude constant - as more drawbars added would typically result in a 'louder' sound.

Shift+Shape:

Tone Shaping Filter Adjustment

Many divider organs provided overall tone shaping by fixed filters applied to the overall signal, selected either via switches or even additional drawbars. With "Divide", we provide this with the shift+shape knob, allowing smooth changes from flute, full(dry) to 'reed' style voicings (effectively acting as an aggresive tone control):

  • 0%: "Flute" voicing - full LOW pass filtering through to :
  • 50%: No voicing applied (dry signal) through to :
  • 100%: "Reed" style voicing (high pass)
This means, that as the 0% value is the full 'flute' voicing, on loading of the oscillator your sound might be a bit 'dull' - set the shift+shape value to 50% to get the full tone.

It isn't perfect, however with the limited number of programmable values in the sdk this does at least provide a voicing solution...

Edit Mode Parameters:

Vibrato Options:
An internal sine LFO for vibrato is provided with this user oscillator with 2 adjustable parameters. Why do we have a separate LFO for vibrato when the synthesizer has its own LFO for this? This is to a: free up the LFO for applying to anything else (e.g. shape), and more importantly, this is how the true "12 note top octave generator vibrato" is emulated - where each top note generator, while being modulated by the same LFO, may not 'quite' get the same amount of LFO applied, again adding a more organic timebre to the overall sound. Use the synthesizer's LFO set to "pitch" if you want the more 'static' global style vibrato provided by a common single top octave divider organ.

    Vib Amount:
Sets the overall amount to apply for the vibrato. Tip: if you're playing live and want to be able to switch this on and off as you play, you might need to disable the oscilloscope meter on your synthesizer - otherwise while you are in this edit menu on this parameter the synthesizer will timeout and go back to the oscilloscope display. .

  • 1 : No vibrato amount
  • 7-9 : about a 'typical' vibrato amount
  • 31 : Maximum vibrato - comically overmodulated.

    Vib Rate:
Sets the internal vibrato sine LFO rate (frequency):

  • 1 : No vibrato rate. If the internal LFO is not at a '0' phase and you apply a vibrato amount, don't be surprised if your notes are now "stuck out of tune"! (at least until the next note on) Your vibrato LFO was frozen in time, and while not typical, is allowed here.
  • 9 : about a 'typical' vibrato rate
  • 15 : Maximum vibrato rate (12hz).
  • Note! A special case exists when the ramp waveform is enabled : The "Hammond Novachord" generated a similar waveform to the ramp wave, so when this waveform is selected we also emulate the unique vibrato generator found on this instrument.
    6x separate unique vibrato LFO oscillators (early models even used electro-mechanical oscillators..!) were implemented, and applied across the 12 top octave oscillators. Thus, different notes would not only have a slightly different vibrato amount, they would have their own unique frequency, yet another feature of the unique sound of this instrument we can emulate here.

    Percussion:

Sets the level of the 4' ("2nd") "percussion" - basically the 4' drawbar has a single shot sawtooth (exp actually) envelope applied to it, adding a 'percussive' sound. To be heard this requires that the drawknob is not on a setting that has the 4' drawbar at full.
Also useful when mixing with the VCOs to add an additional 'pluck' or percussion to your sound.

    Detune

Adjustable from 0 to 100%, this sets how much the top octave generators are out of tune with each other.
  • At 0%, they are perfectly in tune (to equal temperament), and with this value we can approximate the 'static' sound of the single top octave generator IC style organs. Note, the two odd mixture drawbars are calculated using the more harmonically 'correct' "Just Intonation", so these will be even more "static" when this value is at 0%.
  • Adjusting this value up allows the 12 individual notes to be out of tune relative to each other. Not only can this thicken up chords, but more importantly, when the mixture drawbar is enabled, the overall timbre will be less 'static' sounding - as the two 'odd' footages used in the mixture drawbar would have their tuning set by the notes they are mixed from, and would be 'out of tune'. This really helps to get closer to a more 'realistic' sound. I tend to prefer this at around 10-13% , adjust to taste.
  • A value of 100% is comically out of tune and generally not useful...

    Wave / Click

Select the waveform and the keyclick amount with a single parameter....
As we only have 6 user parameters available to us, I have combined 2 parameters into a single value.
Keyclick - Some organs would generate an audible 'click' when notes were pressed down as multiple keycontacts were being closed when keys were being pressed - we can add an adjustable amount of keyclick here.

The "left" digit selects the wave type and the "right" digit (from 0-9) selects the amount of keyclick, as follows:

  • 1-9 : Square wave, with 9 levels of keyclick (1 = no click 9 = full click). This is a slightly rounded square as if it was fed through a simple 6db low pass filter. Many combo organs used this waveform, including some notably orange ones...
  • 10-19 : 25% Pulse Wave, with 10 levels of keyclick (10 = no click 19 = full click). This waveform too has the "6db filter" applied to round the edges. Combo organs too used this waveform, particularly those of grey colour...
  • 20-29 : Exponential Ramp Wave, with 10 levels of keyclick (20 = no click, 29 = full click). This waveform approximates the waveform generated by some divider organs and synthesizers, notably the Hammond Novachord. Notably, when this waveform is selected, the Vibrato will use 6 independent LFO oscillators to approximate the 6x vibrato architecture of this instrument as well.
  • 30-39 : Sine Wave, with 10 levels of keyclick (30=none, 39 = full click). Not originally intended to be included, I added them on a whim - and found them to be far more useful than I expected. Can be used to approximate a more 'tonewheel' sound vs a 'divider' sound.

    Mod Effect

Here we can add some fun and motion to the sound by modulating it with the SHAPE LFO. This will require you to select SHAPE as the destination for the LFO.

  • 1 : No effect - Shape LFO does nothing.
  • 2 : Global Tremolo - Shape LFO modulates the overall amplitude of this oscillator.
  • 3 : Mixture Tremolo - Shape LFO only modulates the level of the IV mixture drawbar.
  • 4 : Auto Octave Arpeggiator - non-resync - Modulates the overall amplitude of the oscillator, however for each repeat of the LFO cycle, the pitch of the oscillator is cycled through a simple sequence of "root, root, -1 octave, -1 octave". The position of the arpeggiator is not re-set when a new note-on occurs.
  • 5 : Auto Octave Arpeggiator with resync - Modulates the overall amplitude of the oscillator, however for each repeat of the LFO cycle, the pitch of the oscillator is cycled through a simple sequence of "root, root, -1 octave, -1 octave". The position of the arpeggiator IS re-set when a new note-on occurs. tip - enable LFO Key Sync with this one...
  • 6 : 3 Octave Upward arpeggiator - For each cycle of the LFO, the octave is cycled through a simple arpeggio of "root, -1 oct, -2oct". Requires at least some LFO INT to be applied to function. Try with minimal LFO INT to get a sound that is changing octaves but is not amplitude modulated. Works with all LFO shapes.
  • 7 : 3 Octave Downward arpeggiator - For each cycle of the LFO, the octave is cycled through a simple arpeggio of "-2 oct, -1 oct, root". Requires at least some LFO INT to be applied to function. Try with minimal LFO INT to get a sound that is changing octaves but is not amplitude modulated. Works with all LFO shapes.
  • 8 : Alternate Repeat - Using a downward sawtooth waveform, modulates certain notes on the positive portion of the LFO cycle and others on the negative cycle. Can be used to get alternating notes "triggering" by simply holding down two notes that would alternate.Requires the sawtooth wave selected at full intensity to function as intended.


Where's my 513 drawbar / "3rd" percussion?!? Well, in short,it isn't there. This was never intended to be a 'tonewheel' organ emulator, and many (but not all) divider organs do not feature this drawbar, never mind that we are limited to only so much CPU time and user parameters.

However, if you really want that sound, you can by all means add it via the on board VCOs. Simply select the triangle wave, and tune the oscillator one "fifth" above the root note, and mix via the VCO level to taste. It can work surprisingly well!


As usual, bear in mind we are still operating within the confines of the logue-sdk architecture, so there are some notable differences vs playing an actual instrument, however it in my opinion can still be a lot of fun, and can open up new and different sounds previously not possible with these instruments.

Hope you enjoy!



This version is built for the 1.0 API, so should be compatible with your synthesizer at any version.

Download the zip here (contains both minilogue and prologue formats)