Analogue Solutions SY02

Gordon Reid checks out a compact filter module that won't break the bank.

Last month we looked at the Concussor Minimodular synthesizer. In passing, I noted that its manufacturer, Analogue Solutions, was also working on the SY02, a dual filter module designed to emulate Korg's popular MS20 filters. Well, with alarming speed, the SY02 has arrived. What's more, the box that landed on the desk at Sound On Sound HQ contains not one, but two of 'em, configured as an ideal add‑on to the Minimodular.

Overview

Each SY02 in the Dual Multimode Filter is 18HP wide, so two of them fit in the AS0036 case that housed the Minimodular itself. To recap, this is a light, plastic moulding with an internal power distribution board powered by an external 12V AC wall wart (for further details, see my Minimodular review in SOS April 2000). The complete assembly is neat and light — so much so that I sometimes had difficulty making it sit still when I was plugging patch leads into the modules themselves.

Each SY02 offers two filters. The first is a 12dB/octave high‑pass device with cutoff frequency and resonance controls, plus a gain control for its associated CV1 input. The second is a 12dB/octave low‑pass filter with its own set of cutoff frequency and resonance controls, and an independent gain control for its associated CV1 input. Underneath these, a VCA offers Initial Level and Volume controls, and the knobby part of the package is rounded off by the Input Level control at the top. Alongside these are eight 3.5mm sockets. These offer two audio inputs, two CV inputs for the HPF (one of which is not affected by the CV Level control), two similarly configured CV inputs for the LPF, and two CV inputs for the VCA. A lone audio output sits within the VCA 'panel'. It's simple, it's neat and, within reason, it offers everything that you would expect in a low‑cost filter module.

If you remove either of the SY02s from the case, you find two trim‑pots on each of their main boards. These allow you to adjust the maximum feedback within the filter circuits, increasing or reducing the maximum resonance to the desired amount. With a trimmer set near maximum, the respective filter will start to self‑oscillate (producing a sonically pure sine wave) when the front‑panel resonance control reaches the one o'clock position. This waveform then becomes progressively louder, thicker, more distorted, and deeper in pitch as you increase the resonance to its maximum. At the other extreme, you can set the trimmers so that neither filter will self‑oscillate at any front‑panel setting. Somewhere between these extremes you will find something that responds like the original MS20.

In Use

Like the Minimodular, setting up the dual filter box is simplicity itself. The preliminary manual does not confirm whether or not the filter and amplifier CVs have the same, unusual ±12V range as those on the Minimodular, but it would be strange if they did not: compatibility is all. Whatever the electrical details may be, I had no difficulty setting the modules up as desired, either in tandem with the Minimodular or when asking an Analogue Systems RS8000 Integrator to provide extra facilities. Indeed, my only complaint at this stage was one that I can not, in all fairness, direct at the Filter box itself. The problem is this: because each of the SY02s has so many inputs, I needed several 'multiples' to direct my CVs to all the inputs I desired. Think about it: if you have a single keyboard CV that you wish to use to control a selection of oscillators and up to four filter cutoff frequencies, you're going to need to split it into five signals. Neither the Minimodular's Dual VCO or SY01, nor the SY02s themselves have any such facilities, so you're always going to need another box of tricks to take care of these matters for you. Shame.

The Sound

The Dual Filter's potential for generating strange and interesting timbres is immense. Forget, for a moment, that it seeks to emulate the idiosyncrasies of the MS20 — just imagine what you can do with four independent, resonant filters. For example, I created monstrous resonant filter sweeps with each of the four cutoff frequencies responding in different amounts to the envelope CV. In a simpler patch, I used the first SY02 and the HPF of the second as static, formant filters (with high Q) and the second LPF as a traditional, swept, resonant filter. This proved to be my favourite mode of operation, because it gave me access to a huge range of subtle timbres that I could tweak using the cutoff and resonance controls of the 'formant' filters.

Both these examples use the SY02s in series, but there is also a huge number of possibilities based around configuring them in parallel. For example, you can set them up as dual, resonant band‑pass filters that sweep some or all of their cutoffs simultaneously. I found that this configuration gave me access to all manner of 'vocal' sounds, as well as even more dramatic formant‑based timbres.

On top of all this, the inputs and resonance circuits of the SY02 are not 'limited', so it's simple to overdrive the filters at many stages in the signal path. This creates many powerful resonances and distortions, and you can have these track the keyboard (for consistent tone) or leave them sitting at defined frequencies. The latter allows you to move 'in' and 'out' of the overdriven ranges as you play up and down the keyboard.

Conclusions

I have just two criticisms of the SY02. The first is that a single SY02 doesn't quite have the bite of the original MS20 filters it emulates. Mind you, the margin is not huge — and in any case, who cares whether the SY02 sounds identical to any given MS20? The important thing is that it comes very close to achieving its aims, providing a set of filters that sound utterly different from the 24dB/octave devices found in the Minimodular and elsewhere.

My second criticism is, perhaps, more significant. I like the self‑oscillation of filters to track the keyboard in a precise 1:1 relationship so that you can 'play' the sound produced. Whether you use this as an additional oscillator, or use the resonance to emphasise certain harmonics in the sound, it's a very important facility for those synths that can do it right. Unfortunately, the SY02 does not track correctly. I know that this is a compromise that helps to keep the cost down; I'm also well aware that the Korg filters do not track 1:1, and that this would be contrary to the MS20's character. But I think a similar filter that did do so would be a killer product.

Overall, however, I was very impressed with the price/performance ratio of the Dual Multimode Filter. Whether you're expanding your sonic palette beyond ubiquitous 24dB/octave filters, are looking for additional filters to enhance an existing synth, or are simply looking for a sound mangler, a pair of SY02s could be just the ticket. Furthermore, a single SY02 is an ideal complement to the 24dB/octave VCF in the Minimodular's SY01, and I could envisage players configuring a filter bank that comprises an AS0036 case, an SY01, and an SY02. And the best thing is that there's nothing to stop you from doing exactly that!