David Rossum is the father to the E-Mu Systems company that created some of the most sought after keyboards and drum machine samplers of all time. The SP-1200, for instance, is indicative to Rossum’s genius electronic musical instrument design. Back in business as Rossum Electro-Music, Rossum introduces the Evolution Filter and his new line of eurorack modules. So, if you ever wondered what it would be like to have Bob Moog and David Rossum collaborate on a product, wonder no more (well, technically it’s not collaboration but you know what I mean… read on).
“In 1973, E-mu Systems introduced their 1100 sub module, which was the heart of their 2100 low-pass filter module. The 1100 used a Moog ladder as its core element, but I wanted to isolate the innate audio characteristics of the filter ladder from those colorations resulting from the input level shifters and output amplifier used in the Moog 904A.” – Dave Rossum
Enter the Evolution Filter is a Variable Character Ladder Filter. It’s very existence it predicated on the idea of David Rossum improving on the well-known classic Ladder Filter design. Rossum elevates the ladder filter idea and expands on it giving it more versatility. Also allowing more CV control, and as the name “Variable Character Ladder Filter” suggests, much more character. The design was plucked right out of his 1973 E-mu Systems modules.
You’ll definitely want to here the Evolution Filter in action. Here is a quick video snippet of the video review which is available on the BboyTechReport YouTube channel now.
I’ll start with the layout and build quality. The Evolution Filter has a really clean look. I love the light grey and blue accented color scheme. The knob placement could bare to have a bit more space but then again, I like the 16HP width as is so I can work with this. While we are discussing the knobs let me just say that these knobs are as smooth as butter. Every tweak is smooth. There is the perfect amount of tension and ease. The knobs feel super solid. There is not an ounce of wiggle or give when tweaking the Evolution Filters parameters.
The module is divided into 4 sections. Frequency, Q, Genus and Species.
@rossumelectro #evolution variable character #ladderfilter one of the best filters in terms of sound and tweakability that I’ve heard as of late thanks to the genus and species features… I’ll show u!👀
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The Frequency Section
The frequency section or column is home to all of the frequency controls. The top knob is the frequency knob. “The actual cutoff frequency is controlled by the sum of this knob and all present control voltages.” The next knob is an attenuator which can be controlled by Freq cv3. Fully left is zero and full right is max. The next knob is an atenuverter which can be controlled ny Freq CV2. At 12 o’clock it’s at zero. Fully to the left, Evolution fully inverts the signal. Fully to the right it passes the full signal.
Freq CV2 is summed with 1v/oct signal. Freq CV3 is summed with both Freq CV2 and 1v/oct singals. As mentioned above, the frequency cut off knob at the top controls the sum of the actual cut off frequency plus all present CV voltages from Freq CV2 and CV3.
The Q Section
The Q section or column is home to all of the resonance controls. “Evolution’s Q section provides manual and CV control of the height of the resonant peak at (or near) Evolution’s cutoff frequency, as well as the level of the frequencies below the resonant peak. (See the discussion of the effect of the Genus setting on the frequency of the resonant peak below.)” The Q knob lets you set the resonance peak. It controls the actual height of the resonance and the sum of all present voltages from Q cv1 & Q cv 2. Q cv 2 is modded by its attenuverter and then summed with Q cv1 and the Q knob. Qcv 1 is a full level control voltage with no attenuator knob.
Typically when sweeping with the Q knob lower frequencies are lost from the audio signals.Q Level compensation knob allows you to compensate for the loss of the lower frequencies when adjusting or sweeping the Q resonance knob. The Q Level compensation knob lets you adjust or add those frequencies back into the signal while keeping the core effect of the resonance on the audio signal.
Here is a taste of the Evolution Filter in self oscillation mode. The full half hour video review is available on the BboyTechReport YouTube channel now.
The Q section is the key to turning this filter into a pure sine wave oscillator. When the Q knob is turned to about 4 volts the filter starts to self oscillate. As described by the manual “In this mode, Evolution acts as a very high-quality sine wave oscillator.” For best results its recommended that the filter be “just barely in self oscillation mode” with the Genus control set to 4 pole.
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The Genus Section
The Genus section or column is home to all of the pole settings. The genus section is one of Rossum’s unique features added to the classic ladder filter design. Genus allows for the control of the number of poles in the ladder filter. The available poles are 3, 4, 5 and 6. Sorry, no 2 or 8 pole modes.
Genus CV2 allows for CV control over the number of poles. Genus CV2 is an attenuverter. It gets summed with the value of the genus knob and the genus CV1. Genus cv 1 is a full level cv that is summed with the Genus knob and the CV2.
The unique deal here is that Evolution allows for sweeping smoothly through the poles. This is very unique.
The following was taken directly from the manual;
The resonant and oscillation frequencies at the various pole settings are:
– 3 poles: resonant frequency is 10 semitones above the cutoff frequency
– 4 poles: resonant frequency is equal to the cutoff frequency
– 5 poles: resonant frequency is 6 semitones below the cutoff frequency
– 6 poles: resonant frequency is 10.5 semitones below the cutoff frequency
The slopes available in Evolution are:
– 3 poles = 18dB/oct
– 4 poles = 24dB/oct
– 5 poles = 30dB/oct
– 6 poles = 36dB/oct
The Species Section
The Species section or column is home to all of the species parameters, CV and knobs. As an over simplified explanation of what the Species control does, it lets you control the ladder filter’s distortion abilities. In oscillation mode the species knob can be used to amplitude modulate at the output. Otherwise, it serves as very musical and pleasing distortion. This is where some very cool overtones start to show up. With no CVpresent full counter-clockwise to 12 o’clock gives subtle distortion. Anything above 12 o’clock is much more pronounced.
Species CV2 and CV1 works the same as the Genus CV does.
Overall, the Evolution filter is one of the most pleasing and fun filters I’ve used. Everything from the basic ladder functionality to the expanded and forward thinking additions of Genus (morphing poles) and Species (distortion). Even the basic ladder filter functionality is expanding in the Q and Frequency sections with the unique (at least that I know of) use of two CV each. One being an attenuator and the other an attenuverter with all incoming CV being summed with the Freq and Q knobs respectively. As if that’s not enough, the Evolution Filter’s self oscillation mode is really solid. With the unique use of attenuators and attenuverters being CV controlled and summed up to the main controls things get very interesting and fun. It offers a very powerful and stable sine wave. Adding in the Genus and Species functionality with CV modulation yields very musical and unique results. This is by far the most fun and unique filter that I’ve used. Rossum does not disappoint.
So if I could be so bold as to pick a bit, I’d love to have seen 2 pole mode in the genus section. I’d also say that the controls are slightly cramped when in full use with patch cables and all. Although, I don’t know that I would prefer any larger of a module to allow for more space between knobs. I’ll just say it’s not a deal breaker. In fact, this Evolution filter is stamped certified dope by Bboytechreport.
Now, I wonder if we can get Dave to reissue the SP 1200. hmmmm.