Epoch Modular TWINPEAK Manual

Module Width: 12hp
Module Depth: 22mm
Current draw: ~35 mA, neg.,
~35 mA, pos.

INTRODUCTION

TwinPeak is a 12db voltage controlled filter designed by Rob
Hordijk. The filter includes a "wave folding" circuit that allows
change to its response-curve—from low pass to variable width
band pass and in between. This response morphing capability is
based on the "inverse-parallel" principle for low pass filters,
where two filters with identical gain can be combined to create a
band pass curve but with two separate peaks at the corners of
the pass band. It is this same principle that forms the basis of
the Twin Peak Resonator in Hordijk's Blippoo Box as well as his
own 5U-18db module.
This set up offers distinct advantages over a low pass/high pass-
series configuration. E.G., in band pass mode, with the curve
knob fully clockwise, the cutoff frequencies of the filters can be
crossed and, regardless of which is tuned higher, the filter output
will be a band pass response. In either case, all frequencies
below the cutoff of the lower tuned filter are suppressed or
subtracted from the filter output.
functionality, we can also set the pass band to near zero
bandwidth with both filters tuned in unison, regardless of the
cutoff frequency.
The inverse parallel architecture of this filter allows for a wide
array of nuances and gradations within its response domain. But
what truly sets this filter apart is its exceptional resonance—ideal
for creating warm, percussive ringings and bell-like effects. The
TwinPeak is specially designed to tilt momentarily into self-
oscillation when pulsed waveforms (even gates, triggers or one-
shots) are used as audio inputs.
duration at low frequencies, e.g.; when either peak is tuned to
approximately 200hz, it will sustain for 4 to 5 seconds.
When the module is used in this way each complementary filter
has a separate, tunable ping. In full band pass mode, where the
TwinPeak is at highest resonance, each ping represents the two
peaks on either end of the pass band. This dual-pinging action
adds another interesting dimension to the filter's sound as the
pings can be tuned and detuned together, in ways that mimic
basic two-string frequency dynamics and the primitive, "sensory
beats" of Helmholtzian physics.
This is a unique and high quality filter that allows for many subtle
possibilities and nuances. It works great with audio frequency
signals, particularly at lower resonance settings, while higher
resonance settings are ideal for creating pings and other
percussive effects. This being said, the module's two inputs and
level/fade control allow one to mix between low frequency and
audio rate signals. Going this route and modulating the filter's
resonance elicits outlandish cross-fertilizations, disclosing new,
hybrid spaces that blur its functional dichotomy.
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!When the frequency of Peak B is higher than Peak A the
*
polarity of the filter output is inverted.
!So, in effect, one can create a broad range of melodic and
percussive effects simply by coupling the module with a step
sequencer and envelope generator.
*
Drawing on this same
†
These pings have a longer
!

MANUAL CONTROLS

Peak Cutoff Knobs: The two knobs at the top of the
panel (Peak A and Peak B) are the manual cutoff
frequency controls for each sub-filter. You will notice that
they have some pop to them, as simply turning either
knob, sans input, produces a ping, much like inputting a
pulse would.
Peak Mod Knobs: Underneath the Peak Cutoff Knobs, on
either side of the panel, you will find these attenuverting
controls for the two sub-filters. As you can imagine, Peak
A Mod and Peak B Mod each correspond to the