XILS Lab PolyKB

Anyone with a passing interest in synthesizers, especially of the unfinished, unobtainable and commercially disastrous variety, knows of the RSF Polykobol II. Few have ever played one — but now there's PolyKB...

Are you still lurking around the backwaters of France with a suitcase of Euros looking for an RSF Polykobol II to complete your collection of large analogue synths? If so, maybe there's no longer a need because PolyKB claims to be an accurate emulation of the fabled French beastie. Its look and feel draw heavily upon the physical appearance of its inspiration, and while the resemblances at first seem stylistic, it soon becomes apparent that there are many similarities (see 'Brief History Of RSF' box).

The Old Stuff

The Polykobol II's oscillators have been recreated in full, including their ability to morph from one wave shape to the next. This allows you to create anything from PWM to more radical tonal changes that cannot easily be obtained by other means. Alongside these, the 24dB/oct low‑pass filter is smooth and powerful. At maximum resonance, it will gently self‑oscillate, and the resulting wave will track the keyboard anywhere between zero and 200 percent. It also has a rather neat feature (not derived from the original synth) that allows you to place overdrive at the filter's input or at its output; the two options create different effects and I like them both. However, there's no external audio input. Unlike many soft synths, PolyKB does not double as a signal processor.

PolyKB boasts two ADSR contour generators, strangely arranged with ADSR2 (which controls the filter) to the left of ADSR1 (which controls the VCA). The Loop2 button (which loops the 'A' and 'R' stages of ADSR2) is welcome, as is the contour time multiplier that appeared in v1.0.1. But the key tracking only affects the Attack stages of the envelopes, which means that it is useless for imitating the responses of plucked or hammered instruments such as guitars, pianos, and percussion. This is daft.

The dual LFOs occupy the same bit of panel space, so you have to select and program them individually. But apart from this slight niggle, they are interesting because, as well as providing a good selection of waveforms, they allow you to select any number of them simultaneously to create complex waveshapes. They can be free running, MIDI sync'd and key‑triggered, but the promised 'Mono' function — which will apply a single LFO to all voices — is as yet unavailable.

The Modulations section combines a traditional mono‑mod and poly‑mod arrangement with a small but very useful modulation matrix offering two sources and eight destinations.The upper two thirds of the Modulations section are reminiscent of a Prophet's, with five modulation sources — LFO1, Noise, ADSR2, VCO2 and velocity — routed (via the mod wheel or not, as you prefer) to the oscillators' pitches and waveforms, as well as to the filter's cutoff frequency. Strangely, the amount of velocity sensitivity has to be determined elsewhere and can only be applied positively so, for example, a higher velocity means that, while your filter cutoff frequency goes up, your contour times are extended and the response slows down! Arghh!!

Like the Polykobol II, the PolyKB features a simple arpeggiator with up, down, and up/down modes. If none of these are selected, it arpeggiates randomly, which is my favourite mode of all. There's a switch that's supposed to extend the arpeggio over an additional octave, but extends it over four, and a silly bug... select 'up' and the arpeggio goes down. Select 'down' and it goes up. Beta‑testers, hang your heads in shame.

Underneath the arpeggiator, the Outputs panel allows you to select the number of voices available (from 1 to 16), the bend range, the velocity sensitivity, the pressure sensitivity, and the amount of analogue 'drift', which isn't drift but random detune. Above this (in the wrong place, really) lie the menus that allow you to select Unison (two to six voices) and your choice from two polyphonic and three monophonic key modes. While the lack of unison detune is weird, overall I like the unison function because it's quite intelligent and always attempts to allocate voices to notes, even if there are too few voices available.

Lurking under what would be the cassette cover on the original synth lies an eight‑voice, 128‑step polyphonic sequencer. Despite the manual's claims to the contrary, this is far from intuitive in use, and its grid‑based interface reminds me of nothing so much as the Roland TR707 drum machine that I was happy to see disappear into the sunset more than 20 years ago.

The New Stuff

The grid‑based sequencer is pure '80s and, unlike the one in the original synth, this one works.

Below the traditional modulation section lies a panel offering two buses that allow you to select two modulation sources from a choice of 12 and direct each to up to four destinations selected from a choice of 29. This is extremely useful, but you can only determine the depths of the sources, not the depths of the modulation applied to each destination. What's more, the routings are uni‑polar so, again, you can't accelerate contours as you play up the keyboard, which is as frustrating as it was a few paragraphs ago.

Again lurking under the cassette cover, you'll find a window that allows you to place each voice in a two‑dimensional 'modulation space', within which you can apply two parameters to the X‑axis and two to the Y‑axis. So, for example, if a voice lies in the bottom left‑hand corner of the space you could define it to have a low cutoff frequency, low resonance, low filter drive, and slow modulation, whereas at the top right it would have a high cutoff frequency, high resonance, high filter drive, and fast modulation. This is a fabulous idea, but the system is hobbled by two omissions. Firstly, scaling is again positive only, so many desirable relationships are impossible. Secondly, the positions are not themselves modulation destinations, which removes any dynamic modification of the voices within this window. Nonetheless, many interesting results can be obtained. Subtle differences between voices add interest, while radical differences can be used to create unusual effects.

At first sight, the PolyKB appears to have two dedicated effects; a simple, sync'able stereo delay, and an even simpler chorus unit. But hiding alongside the sequencer and modulation space you'll find a display in which you can position each voice in a virtual 'room' with two microphones (whose positions and directions you can adjust) on one wall. This is a great idea because, in theory, you could control the pan, loudness, pre‑delay and reverberant quality of each voice using this. Unfortunately, the spatial effects are not yet implemented, but you can still obtain some interesting results, and five presets will help to get you started.

In Use

The Modulation Space allows you to position each voice within a space defined by two parameters on the X‑axis and two parameters on the Y‑axis. Create subtle variations in voices or wild effects, as you wish.

Installing the PolyKB is simple and, provided that you have Internet access, it can be licensed on your existing iLok or the company's own Synchrosoft dongle. It will then run as an RTAS and VST plug‑in under Windows XP, Vista and 7, and as an RTAS, VST and AU plug‑in on Macs running OS 10.3.9 and later. However, there's no stand‑alone version; PolyKB is a plug‑in only.

The toolbars and patch management share much with XILS3 (reviewed in SOS August 2010) and the soft synths that XILS Lab founder Xavier Oudin helped to develop at Arturia, so we need say no more about them here. However, I have to comment on the GUI itself. It's too dim. In bright light, it's hard to read the legends (some of which are also obscured by the shadow rendering) and some of the smaller controls can be all but invisible. Also, at 1400 pixels it's too wide for many computer screens. There's a 1200-pixel option available, but while I was able to select this within Digital Performer, I was unable to do so within Plogue Bidule, so it may be of limited use.

For much of this review, I investigated the PolyKB using a Korg MS20iC controller, and I was able to map its most important parameters to the Korg in just minutes. What's more, those settings were retained no matter how much I abused my Mac and the software hosts over the course of the review. But when I started programming and playing sounds, it became apparent that PolyKB is still a work in progress, because it exhibited numerous bugs and idiosyncrasies. Some of them are silly and no doubt easily corrected. For example, the default value for the master tune is not zero, it's +48 semitones. Others are just odd, such as clicking on [Close] to open the virtual room, modulation space and sequencer windows. Some are a little more involved, such as a bug in the modulation section that causes the mod wheel to affect the depth of the cyclic waveforms but not the S&H output. Yet others are elusive, such as occasional problems getting the LFOs to sync together when both are being driven by MIDI clock. But I am assured that XILS Lab are already fixing these, as well as looking to complete the stereo space algorithm.

The Stereo Space window allows you to position each voice within a virtual room. Not finished as yet, this idea holds great promise, especially if the positions become modulation destinations.So, ignoring the niggles, what's PolyKB like as a synthesizer? The first thing that I noticed was its lack of aliasing. Many soft synths claim this, but few if any deliver. Similarly, high-quality engineering is apparent in the filter response, because there's no significant stepping — just a smooth response from the lowest to the highest cut‑off frequencies. Perhaps as a consequence of this, PolyKB lends itself to warm, rounded patches of the, 'if only the Minimoog had been polyphonic' variety. All the clichés are here, so I won't bother listing them. That's not to say that it's incapable of edgier sounds, nor even of the more precise timbres of analogue/digital hybrids, but when you first lay hands on it, I'll almost guarantee that the first sounds you create will be big, chunky, and imposing. Given the similarities of the Polykobol II's architecture to that of the early Prophets (SSM filters, mono‑ and poly‑mod, and so on) this should perhaps be no surprise. But when you start to use the PolyKB's more esoteric features, the range of sounds that you can produce steps way beyond what was possible in the '70s and early '80s. Happily, these sounds retain the same musical quality as more basic patches, and although you have to be careful to avoid glitches and pops when using wave morphing, there's a lot of scope here for both subtle and experimental sound design.

Alternatively, if you're an aficionado of 1970s electronica or 1990s trance, you'll want to experiment with the sequencer, especially when using the pitch and velocity values of the notes as sources in the modulation matrix. These paths apply only to the voices being played by the sequencer, not those that you may be playing on the keyboard at the same time so, with careful programming, you can play one sound from the keyboard and have a different one accompanying it, even though there's only one patch in use. Fortunately, this is not as complex as it sounds, and you'll soon find yourself deep in Tangerine Dream territory, circa 1980.

Conclusions

Before concluding, I feel that you ought to know that my girlfriend is gorgeous; the spitting image of Helen of Troy. If you saw the two of them in Waitrose, you wouldn't be able to tell them apart. What do you mean, you don't believe me? How can you know? Good. I'm glad we've sorted that out.

So what of PolyKB? Ignoring meaningless comparisons, I found it to be an intriguing synth. I like the oscillators, I like the filter drive, I like the extended modulation facilities, and when the stereo 'space' effect is finished, I suspect that I will like that too, especially if the positions of the voices become modulation destinations. (Believe me, that would be something special.) OK, there are a couple of things that I don't like much, but once the bugs have been zapped and all the features are finished, I expect it to be one of my favourite soft synths. There's a knobbled but dongle‑free demo version available from the XILS Lab web site. I recommend that you try it.