The Classic Ladder Filter, Evolved
At the core of EVOLUTION is Dave Rossum's enhancement of the iconic Moog ladder filter from the original E-mu Systems 2100 LPF module, which Dave counts as his favorite sounding of all the analog filters he designed.
For EVOLUTION, Dave has designed new capabilities that not only allow you to dial in all of the outstanding qualities of the original 2100, but combine to let you create the sonic characteristics of a wide variety of other filter types.
Taken together, EVOLUTION gives you everything from the platonic ideal of the classic ladder filter to a vast selection of alternative filter characteristics.
And like all Rossum Electro-Music modules, it's solidly built, with machined aluminum knobs and high quality components throughout.
Specifications
| Topology | enhanced Moog/E-mu 2100 ladder |
| Poles (Genus) | 3–6, continuously CV-variable |
| Effective slope | 18–36 dB/oct |
| Character (Species) | varies ladder drive & distortion intensity |
| Resonance | voltage-controlled, with Q Level Compensation |
| Self-oscillation | Species modulates output amplitude |
| Exponential generator | accurate, temperature-stable |
| Tracking range | 10 octaves |
See It in Action
Overview: a tour of EVOLUTION's variable-character ladder filter.
Sound demonstration
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Introduction video
Parameter demo
Sound demonstration
Species (Distortion)
A Ladder Filter with Continuously Variable Character
EVOLUTION starts from the classic transistor-ladder topology and adds controls that let one filter span the sound of many.
Genus: the number of poles. A traditional ladder filter has a fixed pole count that sets its rolloff slope. EVOLUTION's Genus control places that under continuous voltage control, sweeping from 3 to 6 poles, an effective cutoff slope from 18 dB/oct to 36 dB/oct. LEDs give continuous indication of the current slope, so you can hear and see the filter change character in real time.
Species: drive and distortion. The Species control varies the signal level into the ladder, letting you control the intensity of the filter's characteristic distortion. In self-oscillation mode it instead modulates the amplitude of EVOLUTION's output.
Resonance and frequency. Resonance is voltage-controlled, with a Q Level Compensation control that balances the resonant peak against the frequencies below cutoff that would otherwise be attenuated as resonance is increased. An extremely accurate, temperature-stable exponential frequency generator (accurate over 10 octaves) rivals the specifications of the best analog VCOs.
"EVOLUTION gives you everything from the platonic ideal of the classic ladder filter to a vast selection of alternative filter characteristics."
Manuals & Guides
Frequently Asked Questions
What is Evolution?
Evolution is a 100% analog variable-character ladder filter for Eurorack. Its core is Dave Rossum's enhancement of the Moog ladder filter from the original E-mu Systems 2100 LPF module, which he has called his personal favorite of the analog filters he designed. Evolution goes beyond a classic ladder by adding voltage-controlled slope (Genus), voltage-controlled drive (Species) and voltage-controlled Q with level compensation. Together these give a wide range of filter characters from one module.
Is Evolution a lowpass-only filter?
Yes. Evolution is exclusively a lowpass filter. Its variable slope (3 to 6 poles) and drive-character controls give it a tonal range that overlaps with what many producers use several filter types for. For highpass, bandpass, notch or shelving responses, look at Linnaeus instead.
What does the Genus control do?
Genus gives continuous voltage control over the number of active filter poles, from 3 poles (18 dB/oct) to 6 poles (36 dB/oct). LEDs show which poles are active in real time. Modulating Genus produces a distinctive "bubbly" timbral effect, because the resonant frequency shifts as the pole count changes.
What does the Species control do?
Species controls the signal level into the ladder core, which sets the intensity of the filter's characteristic distortion. Turning it up drives the ladder harder for more harmonic saturation. The output gain is compensated inversely. The overall level stays consistent while the tonal character changes. When Evolution is used as a self-oscillating VCO, Species doubles as an amplitude modulator.
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Sound & Function
How does the Q compensation work?
Classic ladder filters lose signal energy as resonance increases. The bass drops out and the sound thins. Evolution's Q circuit compensates for this and maintains a consistent signal level even at high resonance. It is a practical improvement over most ladder filter designs.
Can Evolution be used as an oscillator, and how do I get a self-oscillating or pinged sound?
Yes. The exponential generator driving Evolution's frequency is very accurate and temperature-stable, rivaling dedicated analog VCOs. Raise the resonance until the filter self-oscillates. It tracks 1V/Oct precisely, which lets you play it as a sine oscillator. For a reset or pinged sound such as kick drums, trigger it with a gate or ping into the appropriate input. The oscillation then restarts on each hit. The exact timbre can drift slightly with temperature.
How accurately does Evolution track pitch when used as an oscillator?
Evolution's frequency control uses a temperature-stable exponential generator that Rossum states is accurate over 10 octaves, rivaling the best analog VCOs. A dedicated 1V/oct full-level Frequency CV input feeds it. When you push the filter into self-oscillation, it behaves as a musically tuneable, sine-like oscillator. That accuracy lets you play the self-oscillation as a pitched voice across a wide keyboard range, not just a resonant effect. The temperature stability also matters for pinged-resonator percussion and tuned drones, where drift would otherwise be audible. Use the dedicated 1V/oct input for pitch tracking, not the attenuated or attenuverter Frequency inputs.
How many CV inputs does Evolution have?
Evolution has 2-3 CV inputs per parameter, with attenuators or attenuverters on more than half of them. That is an unusually large amount of CV control for a filter module.
What makes Evolution more than a classic ladder filter?
Evolution does far more than a classic ladder filter. Its Genus (variable slope) and Species (variable drive) controls, together with extensive CV inputs, set it apart from a simple fixed-slope ladder. A basic ladder gives you an immediate lowpass sweep. Evolution adds voltage control of slope, drive and compensated Q. You can sculpt evolving, complex textures from one filter.
Comparisons
How does Evolution compare to Morpheus?
Evolution is analog and gives you one deep, controllable lowpass character. Morpheus is digital and gives you 289 multi-pole filter configurations in a 3D morphable space. Evolution suits classic analog filtering with extensive modulation. Morpheus suits sound design and exotic timbral effects. Many users own both.
How does Evolution compare to Linnaeus?
Evolution is a lowpass-only ladder filter with variable slope and drive. Linnaeus is a stereo state-variable filter with continuously variable filter type (LP/BP/HP/notch/shelving), thru-zero FM and an internal modulation oscillator. Evolution is strong on analog warmth and harmonic richness. Linnaeus is strong on versatility and stereo processing. For traditional filtering, Linnaeus covers more ground. For the deepest analog lowpass character, Evolution is the choice.
Specifications & Power
How wide is Evolution and will it fit in my case?
Evolution is 16 HP wide and 25 mm deep. It fits any standard Eurorack case, including shallow skiff-style cases.
What are Evolution's power requirements?
Evolution draws 85 mA on +12V and 75 mA on -12V. It uses a standard 16-pin Doepfer-style connector, needs no +5V rail and is reverse-polarity protected.
What are all of Evolution's inputs and outputs?
Evolution has one signal input (3.5 mm mono, 100 kΩ) and one signal output (3.5 mm mono, 1 kΩ), plus nine CV inputs grouped by parameter. Frequency has three inputs: an attenuated input (min 50 kΩ), an attenuverter input (100 kΩ) and a dedicated 1V/oct full-level input (100 kΩ). The Q, Genus and Species parameters each get two CV inputs, a full-level input and an attenuverter input, both 100 kΩ. Every core control can therefore be voltage-controlled independently. Attenuverters let a single modulation source scale or invert its effect. The dedicated 1V/oct input is what lets Evolution track pitch accurately when self-oscillating.
Troubleshooting
What are the trim pots on the back of Evolution for?
The trim pots on the back are factory calibration trimmers for fine-tuning the filter's response and tracking. Most users never need to touch them. They are set at the factory.
My self-oscillation kick drums drift in timbre.
Self-oscillation behavior can be sensitive to temperature. Allow your case to warm up for 10-15 minutes. Internal PCB trim pots may also affect it. For the most stable kicks, use an external reset trigger to restart the oscillation cycle consistently.
The faceplate color doesn't match my other Rossum modules.
Some production runs have slight color variation in the silver faceplate finish. This is cosmetic only and does not affect functionality.
