Rossum EVOLUTION User manual

EVOLUTION
Variable Character
Ladder Filter
Copyright 2016 Rossum Electro-Music LLC
www.rossum-electro.com
Operation Manual

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Contents
1. Introduction 3
2. Module Installation 4
3. Overview 6
4. Input and Output 7
5. Frequency Control 8
6. Q Control 10
7. Genus Control 12
8. Species Control 14
9. Specifications 15
10. From Dave’s Lab: The Evolution of EVOLUTION 16
11. Acknowledgements 19

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1. Introduction
Thanks for purchasing (or otherwise
acquiring) the Rossum Electro-Music
Evolution Variable Character Ladder Filter.
This manual will give you the information
you need to get the most out of Evolution.
However, the manual assumes you already
have a basic understanding of synthesis and
synthesizers. If you’re just starting out, there
are a number of good reference and tutorial
resources available to get you up to speed.
One that we highly recommend is:
Power Tools for Synthesizer Programming
(2nd Edition)
By Jim Aikin
Published by Hal Leonard
HL00131064
Additionally, for the technically and/or
historically minded among you, check out
Section 10, The Evolution of EVOLUTION, for
Dave’s account of how Evolution came to be.
Support
In the unlikely event that you have a problem
with your Evolution, tell us about it here:
http://www.rossum-electro.com/support/
support-request-form/
… and we’ll get you sorted out.
If you have any questions, comments, or just
want to say “Hi!,” you can always get in touch
here:
http://www.rossum-electro.com/contact-us/
… and we’ll get back to you.
Happy music making!

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2. Installation
As you will have no doubt noticed, the rear of
Evolution is a circuit board with exposed parts
and connections. When handling Evolution,
it’s best that you hold it by the edges of the
front panel or circuit board. It’s not particularly
easy to blow up, but why take chances?
More specifically, the biggest risk (to the
extent that there’s a risk), is damage by static
electricity. Particularly on dry, cold days (or if
you’ve just shued across your shag carpet in
fuzzy slippers), make a point of touching the
metal panel first, before touching any other
part of the module.
While all Rossum Electro-Music modules are
protected against reverse polarity damage,
both to your module and your system, care
should still be taken to connect the power
cable correctly. (For more detail on our
unique protection method, check out Dave’s
discussion of Circuit Protection in Section 10.)
Plug the included 16-pin connector into the
header on the rear of the module such that
the red stripe on the cable (the -12V side) is on
the same end of the header as the “Red Stripe
`-12V” text on the PCB.
Evolution requires, at most, 85mA of +12V
and 75mA of -12V.
We have included both M3 and M2.5 (for
vector rails) mounting screws. Use what fits
your system.
If rack rash is of concern to you, use the
included nylon washers when mounting
Evolution in your case.

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Taken together, Evolution gives you
everything from the platonic ideal of the pure
classic ladder filter to an almost unlimited
selection of alternative filter characteristics.
In the following sections, we’ll look at each of
Evolution’s functions in turn.
3. Overview
Evolution is a pure analog lowpass filter
that oers — in a single module — the
characteristics of a wide variety of synthesizer
filter types.
At the core of Evolution is Dave’s unique
implementation of Bob Moog’s iconic ladder
filter from the original E-mu Systems 2100
LPF module (which, incidentally, Dave counts
as his favorite sounding of all of the filters he
designed). Check Section 10 to learn what
made the 2100 (and, consequently, Evolution)
so special.
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
characters of other synth filters that are not
otherwise possible with traditional ladder
filters.
They include:
>A Genus control that allows voltage
control of the number of filter poles,
allowing a range of entirely new and
striking audio eects.
>A Species control that allows voltage
control of the signal level into the ladder,
letting you control the intensity of the
filter’s characteristic distortion.
>Voltage controlled resonance with a
variable Q Level Compensation control
that lets you control the balance of the
resonant signal and the frequencies
below the cuto frequency (which would
otherwise be attenuated as the resonance
is increased).
>An extremely accurate and temperature
stable frequency control exponential
generator, rivaling the specifications of the
best analog VCOs

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4. Input and Output
The Input and Output jacks let you get audio
into and out of Evolution.
Evolution is DC coupled throughout, so you
can use Evolution to process CVs as well as
audio.
The Input expects a signal level up to 20Vp-p
Depending on the Input level and the settings
of the various controls, the Output provides a
signal level of up to 20Vp-p without clipping.

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5. Frequency
Evolution’s Frequency
section provides
manual and CV control
of Evolution’s cuto
frequency (i.e., the
frequency above which
the amplitude of the
signal is attenuated).
FREQUENCY Knob
The FREQUENCY
knob allows you to set
Evolution’s initial cuto
frequency (I.e., the cuto
frequency when no
CVs are present). The
actual cuto frequency is
controlled by the sum of
this knob and all present
control voltages.
Without CVs present, the
range of the control is
from approximately 22Hz
to 22kHz. With CVs, the
available range is from
.02Hz to 40kHz.
When Evolution is in
self-oscillation mode (see
the Q section below),
this control sets the initial
frequency of oscillation.
NOTE: Refer to the
Genus section below
to understand how the
Poles setting aects the
oscillation and resonant
frequencies.
1V/OCT CV Input
The 1V/OCT CV Input is a calibrated full
level control voltage input that is summed
with the value of the FREQUENCY knob
and the FREQ CV2 and FREQ CV3 inputs.
When properly calibrated (as it will be when
delivered), Evolution’s 1V/Octave tracking
is accurate over a 10 octave range (better
than many Eurorack VCO modules). When in
self-oscillation mode, Evolution serves as an
extremely high quality sine wave oscillator.
FREQ CV2 Input
The FREQ CV2 Input is a control voltage
input that is modified by its associated
attenuverter and then summed with the value
of the FREQUENCY knob and the FREQ CV3
and 1V/OCT inputs.
When the attenuverter knob is set to its “0”
position, no control voltage is passed to
the filter. As the knob is turned clockwise
from 0, the amplitude of the control voltage
increases until, at maximum clockwise
rotation, the full amplitude of the signal at the
FREQ CV2 Input is passed through and results
in a nominal 1V/Oct response.
As the knob is turned counter-clockwise from
0, the signal at the FREQ CV2 Input is inverted
(e.g., a CV of +2.5V becomes -2.5V). The
farther counterclockwise the knob is turned,
the less the attenuation of the inverted
signal, until, at maximum counter-clockwise
rotation, the full amplitude of the inverse of
the signal at the FREQ CV2 Input is passed
through, also at a nominal 1V/Oct response.

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FREQ CV3 Input
The FREQ CV3 Input is a control voltage
input that is modified by its associated
conventional attenuator and then summed
with the value of the FREQUENCY knob and
the FREQ CV2 and 1V/OCT inputs.
When the attenuator knob is set to its
maximum counter-clockwise position, no
control voltage is passed to the filter. As the
knob is turned clockwise, the amplitude
of the control voltage increases until, at
maximum clockwise rotation, the full
amplitude of the signal at the FREQ CV3
Input is passed through at a nominal 1V/Oct
response.

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6. Q (Resonance)
Evolution’s Q section
provides manual and CV
control of the height of
the resonant peak at (or
near) Evolution’s cuto
frequency, as well as the
level of the frequencies
below the resonant peak.
(See the discussion of
the eect of the Genus
setting on the frequency
of the resonant peak
below.)
Q Knob
The Q knob allows you
to set the initial height
of Evolution’s resonant
peak (I.e. the height of
the peak when no CVs
are present). The actual
height of the resonant
peak is controlled by the
sum of this knob and all
present control voltages.
This control produces a
voltage range of between
0V and 7V.
When the Q knob is
turned clockwise to
about 4V, the filter will
enter self-oscillation
mode, producing a pure
sine wave. In this mode,
Evolution acts as a very
high-quality sine wave
oscillator.
NOTE: The purest sine
wave and the most
accurate tracking occur
when the filter is just
barely into oscillation and
the Genus control is set to
4 poles.
ANOTHER NOTE: Refer to the Genus
Section to understand how the Poles
setting aects the oscillation and resonant
frequencies.
YET ANOTHER NOTE: Also refer to the
Genus Section to understand how the
Q setting aects oscillation during transitions
from one pole setting to another.
Q LEVEL COMPENSATION
In a traditional resonant ladder filter, as the
height of the resonant peak is increased, the
levels of the frequencies below the resonant
peak are attenuated. When the cuto
frequency is swept manually or by a control
voltage, the result is the familiar classic “wah”
we’re all familiar with.
In many cases, that’s exactly what you want,
as at high Q, you can hear the filter pick out
each overtone (or “frequency” of noise) as
you sweep through the audio spectrum.
However, if what you want is to add some
resonant spice to a pad or fat bass sound, the
lower frequency attenuation that results from
turning up the Q results in sucking some (or
most) of the guts out of the sound, leaving it
sounding thin.
Luckily, Evolution gives you a choice with the
Q LEVEL COMPENSATION control.
With the control turned fully counter-
clockwise, there is no compensation and the
filter acts exactly like a traditional ladder filter.
As you turn the control clockwise, the
amplitudes of the frequencies below the
cuto frequency are progressively boosted
until, at full clockwise rotation, they are at
their full (pre-attenuation) level.
Simply dial in the exact level of compensation
you want for each particular patch and you’re
good.