Frostwave Resonator

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I've been a big fan of the Korg MS-20 ever since it was my first synth back in the early 80s. I especially like the filters - both the sound and the way the controls are arranged on the panel. It's only recently, within the last couple of years (after trying a fair number of other synths) that I realized I had something unique here. So I was naturally intrigued when I heard about the Frostwave Resonator, which is a clone of the MS-20 filter section. I couldn't resist trying this out and comparing it to the MS-20. Here is what I found. ms20sm.jpg (22124 bytes)
ms20filter.JPG (18436 bytes) The MS-20 filter section consists of a 12db highpass filter and a 12db lowpass filter in series. There are two large knobs to control the cutoff of each, and two more smaller knobs to control the resonance, or "peak". Below that there are two knobs for modulation of the cutoff frequency (routed internally from the MS-20 modulation generator). The modulation generator has a rate control, and a shape control that allows a continuous range of square/pulse or saw/triangle/ramp waveforms. Finally there are two knobs that control either the envelope amount, or the amount of an external modulation source routed via the patch panel.

This layout, with conveniently located knobs for full control of both filters, is what makes the MS-20 so great for real time sound mangling. With two hands you can fairly easily manipulate six filter parameters, allowing a tremendous range of expression. All of the controls can be pushed to the extreme, leaving any notions of "moderation" up to the musician. After playing with the MS-20, I have found single knob cutoff sweeps to be rather boring.

Characterizing the sound is always subjective, but I think of it as gritty, grungy and especially growling on the low frequencies. I suppose the filters could be used to produce smooth, soothing sounds, but what fun is that? It is ironic that when Korg designed the MS-20 they were trying to build something that could emulate acoustic instruments. (See the patch book that came with it).

The first thing I noticed when I looked up the Frostwave Resonator, was that it didn't have my favorite modulation controls from the MS-20. In fact it doesn't have an LFO, but fortunately there are CV inputs for LP frequency, HP frequency, LP resonance and HP resonance. Actually this goes beyond the MS-20, which does not have any LFO modulation or external controls for the resonance. I decided to pair up a Moog CP-251 control processor with the Resonator, to give me a wide variety of modulation controls. I really like this combo, which gives me all the functions of the MS-20 filters and more, for a total cost of about $400. The CP-251 has an LFO, sample and hold, lag processor, mixer, multiple, and attenuator sections. Here's a picture of the setup:

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To see how accurately the Resonator reproduces the sounds of the MS-20 filters, I did a couple of side-by-side tests. First I put them each into self-oscillating mode by cranking up the resonance (LP only, HP only, and both). There are a couple of minor differences in the feel. The MS-20 has frequency knobs on top, and resonance below, whereas the Resonator reverses this (both place the HP filter on the left and the LP filter on the right). Also the frequency knobs on the Resonator are smaller, resulting in a somewhat faster response. Doing some filter sweeps with the resonance up, the sounds are almost identical. I did notice one slight difference. When both HP and LP resonance are cranked, and the HP frequency is near minimum, you can hear the low frequency beating of the HP resonance. On the Resonator it is a kind of pitched chirping sound, but on the MS-20 it is noisier, or perhaps has a more variable frequency. The MS-20 is a bit grittier, not as clean sounding. One could argue that the Resonator sound is actually better, but I think I prefer the grittiness of the MS-20 in this particular case. This is not a big difference, and I was specifcally looking for anything that was not an exact match. It could be that this is attributable to variations that are within the tolerances of the individual components, in which case they might also be noticeable between any pair of MS-20s. It would be interesting to compare two MS-20s to see how close the sonic properties match.

For my second test I took a saw wave from the MS-20 and ran it alternately through the MS-20 filters and the Resonator, performing various filter sweeps. Again the two sounds were virtually indistinguishable, except for the case of some noticeable difference in the artifacts when both HP and LP resonances were cranked. Overall I would say there was a 99% match, with the difference being probably not musically significant, and possibly due to individual variations between components.

To be complete, there is one very minor glitch I discovered with the Resonator. There was an audible click while turning the dry/wet balance knob just after the bypass is switched off. Not a big deal as you wouldn't normally be using both the bypass switch and the dry/wet balance (clue: one is intended for hands, the other for feet). The bypass switch itself also makes a loud click, but I guess that is to be expected.

In summary, if you are a fan of the MS-20 you will love the Frostwave Resonator. Or if you always wanted that sound but didn't want to deal with yet another synth, this is just the ticket. It is well made, sounds clean but nasty, as close as you can get to the real thing. I recommend using it with the Moog CP-251 or some other CV modulation source to achieve the full potential wildness of the MS-20.

btzbul1a.gif (1801 bytes)  Frostwave Resonator   btzbul1a.gif (1801 bytes)
btzbul1a.gif (1801 bytes)  another Resonator review by Norman Fay  btzbul1a.gif (1801 bytes)
btzbul1a.gif (1801 bytes)  Moog CP-251  btzbul1a.gif (1801 bytes)
btzbul1a.gif (1801 bytes)  Korg MS-20  btzbul1a.gif (1801 bytes)

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updated October 29, 2007    --- egw ---