Review – PolyKB II by XILS-lab

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Looking for the classic analog warmth and charm of those hardware synthesizers from the past?  PolyKB II is a serious competitor in the virtual analog marketplace.  Find out more in this review.


by Rob Mitchell, July 2015


XILS-Lab is a music software company located in France, and they are the designers of many excellent music software products. These include several synthesizer plugins, effects, and sound sets. XILS 4, Syn’X, Oxium, and XILS V+ are just some of their wide-ranging products.

For this review, I will be covering PolyKB II. It is their software emulation of the RSF PolyKobol synthesizer; a two-oscillator, subtractive polyphonic synthesizer. One of its most notable features is its continuous morphing oscillators. It also includes an arpeggiator and its own polyphonic sequencer. It was tough to even find one of these original hardware synths back in the day, as there were only around 30 of them built. Thanks to modern computer programming, we are lucky enough to have a reproduction of this rare and powerful synthesizer in software form.

XILS-Lab’s original version (PolyKB) was first released back in April of 2010. They later improved it with fixes for many of the bugs that were found. Changes were made to the modulation sections as well, and they enhanced the factory sounds. This new version is what is now known as PolyKB II.


Installation Requirements

The minimum system requirements for PolyKB II aren’t too high: One gigabyte of RAM, and a 2 GHz CPU. It will work on PCs with XP, Vista, or Windows 7, and is in VST and RTAS formats. The manual doesn’t mention anything about Windows 8. On a Mac, it will need OS X 10.3.9 or higher, and it comes with VST, Audio Unit, and RTAS formats. There is no standalone version of PolyKB II.

PolyKB II does require iLok, but XILS-Lab has recently enhanced their software to work with the software version of iLok. This way, you don’t need a physical iLok dongle. I used the software version (no dongle) during the writing of this review, and it worked without issue on my Windows 7 PC. You just need to setup a free account on the iLok website, and download the license manager software. When you run the installation, it will prompt you for what type of format(s) you’d like to install, and ask you where the plugin and where the presets should be installed.


First Impressions

When it is first started, you’ll see PolyKB II’s many controls. The display itself has a nice look to it, and can be switched between three different sizes from the “Options” menu at the top right. The choices available are 1000p (1000 pixels across), 1200p, and 1400p.  After you change it to one of these other sizes, it will switch to the newly selected size the next time the plugin is started up.

Before learning where all the controls are, and what does what, you might like to just check out some of its presets. Across the top is the main toolbar which has some menus for navigating through the included presets. The initial preset it loads with is a simple one-oscillator Init preset. This is just a very simple, initialized preset that has basic settings. They are useful for starting from a blank slate, so you can create your own presets.

If you click on the “Preset” menu, you will see a selection of the many other Init presets that are included. This is the way it starts up by default, and there are a good number of these to choose from. Some of these Init presets include Unison Poly, Two Osc Pad, and many that use synced oscillator settings.

Using the first menu button, you are able to switch to different categories, including Author, Feeling, Type, Style, Bank or Projects. To the right of that first button is a field that displays the list of what’s included in the category you have selected. For instance, you can select Type, and then you would get a list with many selections of preset types, such as Init, Bass, Brass, Lead, Sequence, and so on. Factory presets can’t be modified and saved in the same directory, so you may notice the Save button is grayed out. You can use “Save as” to save it to another directory however.

If you set the second menu button to Author, you’d then see all the presets designed by a certain author for that type of preset. The next field to the right displays the presets that match those criteria. The menus work fairly well and I didn’t really miss having a large display showing all the different categories of presets, categories, and their names.



At the heart of every synth plugin are the oscillators. In PolyKB II, there are two oscillators: VCO1 and VCO2. Each of them have Frequency and Waveform knobs, letting you change the tuning and the waveform used for each oscillator. If you need to use some fine tuning, you just hold down the Shift key while turning the Frequency control.

One special function that the PolyKB II has in its bag of tricks is that the waveforms can morph into each other. It is a very smooth transition as you turn the waveform control, and it sounds great as it blends between them.

Below the first oscillator (VCO1) are two switches which control its volume level. If neither is selected, there is no volume at all. If you just turn on the first switch, it will be at 1/3 of its volume level. If you only turn on the second switch, it is about 2/3 of its volume level. Finally, with both of them switched on, it will be set to its full volume.

The second oscillator has a standard volume control, letting you dial in the amount you’d like. To the right of VCO2’s controls are some additional switches. Some of these include Detune, Synchro, Key Off, and Lower. 

The “Detune” switch will put VCO2 just bit out of tune with VCO1, a quick/handy way to give a different character to the sound. As you might have guessed, “Synchro” enables hard sync between the two oscillators. “Key Off” changes VCO2 so it won’t follow the pitch of the keyboard. “Lower” changes the function of VCO2 so it acts as an LFO, with its rate changing depending on the pitch of the note.

PolyKB II also includes unison, and can have up to six voices enabled. In addition to the two oscillators, a noise generator is on board as well. It’s capable of producing white or pink noise. The noise volume level can be changed the same way as VCO1, and you’re able to use it as a source in the modulation section. It also includes a filter which can get rid of the high frequency noise. This filter can be switched on by clicking the green LED below the switches.


Filter, Envelopes, and LFOs

The filter included in PolyKB II is a four-pole low-pass, and it can self-oscillate. This is a straightforward part of the synth, with standard cutoff and resonance controls. It also includes an adjustable Drive control, and it can be used before or after the filter. This can give it some more “bite” and saturation, adding some additional character to the sound.

There are two more controls at the bottom of the filter section. The first one controls the keyboard follow for the filter cutoff, and the other adjusts how much of ADSR2 (the second envelope) is used for the cutoff modulation.

PolyKB II has two ADSR envelopes. The first envelope (ADSR1) is for the amplitude, and the other envelope (ADSR2) is routed to the filter cutoff. You can also assign them in other ways over in the modulation section, which I’ll get to later.

The envelope section has a few extras built-in. In-between the two columns of envelope controls, there are three switches which can be used to control various functions. The first one is labelled “MUL” (for multiply), and lets you quickly change the ADSR’s values. It will multiply them by up to four times their original settings. “LOOP2” makes it so ADSR2 will keep looping the envelope, going from its attack stage to the release stage until you release the key. The “KEY TRCK” switch will turn on (you guessed it) key tracking.

There are two LFOs included in PolyKB II. You are able to switch between them by clicking on the label at the top, where it says “LFO 1”. The controls include a rate knob, and many switches for the different waveform shapes that you can use with the LFO.

Waveforms for the LFOs include Sine/Triangle (switch between those two by clicking its label), Square, Ramp up, Ramp Down, and Noise. They can also be used in combination, and this can bring together more complex sound shapes to the table. Switching on the “MID S” (MIDI Sync) will sync the LFO to the host. Down below the other controls are two additional knobs that can affect the LFO. “Delay” will keep the LFO from affecting anything for a certain amount of time, and the “Fade” control will slowly fade in the amount of the LFO on the specified target.


Modulation Matrix Sections

A modulation matrix is basically where you can setup sources to affect different parts of a synth. Usually, you are able to do things like set an LFO to change pitch of an oscillator by a certain amount or have it set to the filter cutoff.

In many synth plugins, there is one modulation matrix to control everything from. In PolyKB II, there are three separate matrixes, giving you a hefty amount of modulation capability for your presets.

The main mod matrix section is in the middle of the display, and is preconfigured with certain sources and targets that you can use right away. This is very easy to use, as it is basically set up for you, and ready to go. It has five sources to choose from, and their levels are controlled by knobs. To the right of the knobs are the switches for selecting what you want to be modulated. Each switch has three states: Off (no light), positive modulation value (green light), or a negative modulation value (red light).

Enabling the “MOD” switch makes it so the mod wheel controls the level of modulation. If it is turned off, then you control the levels with the regular amount knobs I mentioned earlier. Enabling the “RST” switch will make the LFO reset for every new note that is played. Oscillator tuning, waveform morphing, and filter cutoff are available as targets for modulation.

Below the main mod matrix section is another matrix, and from there you can access modulation choices from dropdown menus. You’re able to map sources to targets from those menus to your liking. This is where you can get to more specific sections of the synth, such as the separate stages of the envelopes, and much more. To see the choices for modulation, you just click the labels that are under the two knobs, or click the labels next to the two rows of switches.

To the left of those two matrix sections is another modulation section. If you’re starting from a basic One Osc Init preset, you won’t see it right away. To open it up and see its options, click on the “Panel” button over towards the left, and then you’ll see a few different choices. The PolyMYX display (which stands for Polyphonic Modulation YX Pad) uses points on the pad that you can drag around to various positions. You’re able to select up to four targets for modulation, and these can be picked by clicking the labels located at each corner of the pad. Each of the modulation targets has an amount knob to adjust its level.

That same Panel button I mentioned before has some other choices available, such as the DynaMYX. This feature will let you position the points on the pad where you’d like, and they affect the stereo placement of the voices. There two menus on the left side you can use with that: “Dyn” affects how the voices will move dynamically, while the “Set” menu has choices of how the voices will be placed around the stereo field. There are two virtual microphones at the bottom of the display that you can adjust to that end. They can be adjusted to different angles, and their stereo width can be adjusted also, changing the way the voices are heard in relation to their positions.


Sequencer and Arpeggiator

PolyKB II includes a polyphonic sequencer, letting you pick up to eight voices. This works pretty well, and combined with the DynaMYX you can get some nice, kinetic arp patterns. Sequencer patterns can also be saved and reloaded later. Initially, it is a little tricky to learn how to use the sequencer, but it is a powerful feature.

My main wish would be to make the display for the notes in the sequence a little wider. Even though there are zoom controls, you can’t see past a certain point in the sequence of notes. The only way to see past the regular field of view is by using the “Rotate” control, which lets you scroll from left to right to see the other notes.

The arpeggiator is not overly complex, making it a breeze to use. The controls include settings for poly mode, ascending or descending modes, octave number, and play mode. The Chord sequence feature lets you enter in up to 32 notes that can be used when in polyphonic mode. Gate and swing controls are also included.



PolyKB II has four effects that you can use in your preset design. These include delay, chorus, phaser, and EQ. To get to each of their settings, you click the label for whichever one you want to edit in the lower right. To switch them on or off, you just use the four switches to the left of the effects section.

The delay can be synced to the host, and has separate left and right channel settings for delay time and feedback amount. The chorus has straight ahead settings of just rate and amount, but also has three chorus types to choose from. The phaser has many more controls, including speed, amount, as well as frequency, resonance (internal audio feedback), and stereo (difference in the phase of the channels). The EQ has two low/high shelf filters. The first filter has a range of 30-3,000 Hz, and the second filter has a range of 3,000-18,000 Hz. Each of the two filters also has resonance and gain controls.



First off, I have to say that I really love the sound of PolyKB II. It has a great analog type of sound, and with nearly no aliasing, as far I could perceive anyway. If I were to make any requests, it would be to just add a few more filters types. They are probably just trying to stick to the original configuration of the PolyKobol for the most part. That is totally understandable, as it is an emulation of that rare hardware synthesizer.

The manual is very well written, and I liked how the table of contents is linked to the different sections.  However, one thing I noticed about the manual is that a few sections have screenshots of the synth display that are very small. Most are of a decent size, but a few of them are just tiny.

For many of the presets, the CPU usage was decent on my older dual-core Windows 7 desktop. On some (but not many) of the more complex presets though, it was maxing it out. On my other i5-based laptop it worked very well, and the CPU usage was not bad at all.

PolyKB II has a superb sound, and I highly recommend it. It comes with great presets, it has a large number of modulation possibilities, and I love the fact that you can resize the display. This really should be a standard feature in all synth plugins these days since so many people request it.

PolyKB II retails for $163 USD, and you can get more information on PolyKB II from the XILS-Lab website here:

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