Review – IVOR2 from Xen-Arts

Another free plug-in from Xen-Arts which features extreme microtonal control and elegant timbre exploration potential.


by Warren Burt, July 2016


Jacky Ligon, composer and software developer who hails from the U.S., is the main force behind Xen-Arts ( a web-site and software development project.   He has produced a number of VSTi instruments over the years, one of which, Xen_FMTS2, featured in Soundbytes in July 2014 ( ).   Now, he’s got a new synth available – IVOR2.   It’s the successor to IVOR, which had 2 oscillators, ring modulation and some elegant modulation possibilities, as well as Xen-Arts signature MIDI Tuning Standard microtonal possibilities.  IVOR2 has most of the features of IVOR, (a few are eliminated, not many, but there are enough differences between the two that I’m not uninstalling IVOR from my computer) and it adds a new kind of modulation module, unique ways of tuning timbre, as well as a range of Frequency Modulation (FM) abilities.

IVOR stands for mIcrotonal Virtual analOg synthesizeR, but is actually named in honor of Ivor Darreg (1917-1994), microtonal music pioneer, who invented a number of microtonal instruments, and who probably wrote more theoretical writings on the possibilities of all the equally-tempered octave-based microtonal scales than anyone else.  In his last decade, with the help of his student Brian McLaren, he composed several sets of electronic etudes which demonstrated the sonic possibilities of these scales.

Just as the first IVOR synth gave possibilities to extend and expand on Ivor Darreg’s work, so this second iteration offers unique possibilities to take that work even further, especially in the realm of relating tuning to timbre.  This point might need a bit of explanation.  Most of the “normal” musical sounds we hear in “the West,” such as guitars and pianos, have timbres in which the partials, or overtones, are arranged in the harmonic series, with the frequencies of each partial related to the other in whole number ratios.  And the scale we play these timbres in, twelve-tone equal temperament, has fundamentals which are “pretty close” to the pitches of that harmonic series.  So most chords are heard as fairly consonant, with very little beating between the notes of the chords.  If, on the other hand, you have a scale such as thirteen-tone equal temperament, where the fundamental pitches don’t relate at all to the harmonic series, and you play chords in this scale using harmonic series-based timbres, the resulting chords will sound very dissonant.  But then, if you can tune the partials of your timbres to the pitches of the thirteen-tone scale, you’ll find that these same chords don’t have a dissonant beating in them anymore, but have a kind of smoothness to them that is quite unique.

With IVOR2, you can modulate your main oscillator with another oscillator which can be tuned to the pitches of the microtonal scale you’re using.  This produces sidebands in the timbre which should be more closely related to the pitches of the scale you’re using, especially if you use sine waves as your starting timbres.  IVOR2 allows a number of different kinds of modulations – frequency modulation of phase, pulse width, or frequency itself, frequency modulation of the phase or pulse-width modulating oscillator, cross-fade modulation (where the two oscillators are cross-faded at audio rates), amplitude modulation, frequency modulation of the filter cut-off frequencies, and “harmonic modulation” where a selectable external continuous controller can modulate the frequency of the main oscillator along the pitches of a scale (user-specifiable) which consists of harmonics tuned to the pitches of the chosen scale.  That is, you can have your oscillators tuned to, say, thirteen-tone equal temperament, then have a file of partials which are also tuned to the pitches of thirteen-tone equal temperament, and arpeggiate your oscillators along an overtone series that is itself tuned to thirteen-tone equal temperament.  And this partial file can control the frequency of any of the eight modulating oscillators as well.  So the possibilities for exploring modulation spectra in which the structure of the tuning and the timbre are, at least to some degree, matched is very great indeed.  I don’t know of any other soft synths in which one can do this.  And of course, there is also the possibility of having your fundamentals tuned to one scale, while your partials file is derived from an entirely different scale.  Again, the possibilities for timbral exploration are very great here.

The key new module in IVOR2 is a new kind of modulation generator (Mod-Gen) which combines two kinds of envelope generators, a low-frequency oscillator, and an audio rate oscillator into a compact unit.  One chooses between the two kinds of EGs (ADSR and an up-to-eight stage graphic envelope with many possibilities for shaping of each stage), and between the LFO and the Audio Rate Oscillator, with drop-down switches, then uses push-buttons and value sliders to turn on and off the EGs and the oscillators, and control their levels.  And as said above, the frequency of the audio rate oscillators can be locked to the pitches of the partials file you choose to load.  You have eight of these versatile beauties, each of which is hard-wired to a particular target, and each of which can also be turned off with a push-button.  The targets for the Mod-Gen are phase or pulse-width (depending on the waveform) modulation of the each of the two oscillators separately, amplitude of the phase or pulse-width modulation of each oscillator separately, cross-fade modulation, filter cut-off frequency, overall amplitude (VCA), and pitch of the oscillators, with the polarity of each oscillator separately controllable.  And remember that each of these controls can be an envelope generator and/or an LFO or an Audio Rate Oscillator, and that the frequency of each of these LFO-AROs can be controlled with an external continuous control (automation) signal, and you can get an idea of the almost mind-boggling complexity that is hidden between IVOR2’s modest faceplate.


The key to the density of the synthesizer being hidden behind this seemingly sparse GUI is the many drop-down menus and on-off switches that exist in each module.  For example, if we take the Mod-Gen as an example, the nine copies of this module are accessed by the drop-down list in the upper left of the module.  Beneath that drop-down list are on-off switches for the EGs and the LFO-ARO.  Beneath those on-off switches are sliders to control the amplitude of the control signal.  And further, if both the EG and the LFO-ARO are selected, then the EG also acts as an amplitude control for the LFO-ARO.  Similarly, in the left half of the module, one selects from a drop-down box to go between the ADSR and the Graphic Envelope generator, and in the right half of the module, a drop-down box selects between the LFO and ARO modes.  So each module in the synth has this kind of multi-purpose graphic interface.  Clearly, when programming new timbres, one needs to keep a good mental map of the functioning of each control signal very well in mind, because just by looking at the GUI, you won’t be able to tell, at a glance, what signal is modulating what.  I found that programming this synth was a step by step operation, with careful listening to the effect of each modulation as it is turned on, or off, and the amplitude and frequency of each is adjusted.


Another example of this density is the right half of the Performance Control module at the top.  In the left side of this module are the slots for selecting and changing tuning and partial files.  In the right half are the controls for the effects.  A drop-down box, again, allows one to select between five different functions: MIDI, Pitch, Mod-FX, Ensemble and Delay.  Further, within the Mod-FX page, there are three choices, again with a drop-down box selector, Chorus, and Phaser 1 and Phaser 2.


The oscillators have 22 different waveforms.  About half of those are able to be phase modulated, for an FM-like sound, and the other half can be pulse-width modulated, for a different class of timbres.  As well, there is a noise timbre available.  The LFO-ARO Mod-Gens have 24 different waveforms to choose from.  There are six different kinds of Cross-Fade Modulation to choose from, and six different kinds of filters.  There are three different kinds of ways of specifying the width of pitch bend, and with the bend, each of the oscillators can have its own polarity – positive, negative, and off.  This means that you could have the two oscillators moving in different directions with the same pitch bend signal.  Turn on Ring Modulation with this happening, and you’ve got a very interesting set of timbres to deal with. 

The Partials file is simply a text file with 32 ratios in it.  These can be any numbers with a whole number followed by a decimal point and up to eight digits.  You can easily make your own, to specify any set of pitches you desire for your partials.  The MTS files need to be made (most easily) with Scala, the free tuning utility ( ) , but once you have Scala, you can set up any microtonal scale imaginable and add it to the library of supplied Scala MTS files.  The plugin comes with a set of very lush timbres by Ligon himself and Sevish, which demonstrate a lot of the potential of the instrument, but you can save your own presets and banks and use those instead.  And almost every parameter of almost every module can be externally automated, or controlled with external MIDI continuous controllers.

This is a very deep plugin.  A slow and meditative reading of the supplied manual is highly recommended, followed by experimentation, parameter by parameter with the settings.  This sounds like a fair amount of work, and it is, but it’s well worth it. The timbral and pitch possibilities of this plugin are immense, and the price is right.  Jacky Ligon’s free suite of plugins are comparable in power with far-from-free commercial products, and they also do things that no other software, commercial or free, can.  Xen-Arts five plugins (to date, more on the way) have become a permanent part of my VST collection, and if you’re at all interested in the world of alternative tunings (or timbral exploration), they should be part of yours as well.

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