Epoch Modular TwinPeak Eurorack Module

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TwinPeak is a 12db voltage controlled filter designed by Rob Hordijk.

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Manufacturer: Epoch Modular

Category: Keyboards & Synths



TwinPeak is a 12db voltage controlled filter designed by Rob Hordijk. The filter

includes a “wave folding” circuit that allows change to its response­curve—from

low pass to variable width band pass and in between. This response morphing

capability is based on the “inverse­parallel” 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 5U­18db module.

This set up offers distinct advantages over a low pass/high pass­series

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 or lower, 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. Drawing on this same 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 across the response spectrum. However, what truly sets this

filter apart is its exceptional resonance—ideal for creating warm, percussive

ringings and bell­like effects. The TwinPeak is specially designed to tilt

momentarily into self­oscillation when pulsed waveforms (even gates, triggers or

one­shots) are used as audio inputs. These pings have a longer 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 dual­pinging 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


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

cross­fertilizations, disclosing new, hybrid spaces that blur its functional



Additional Info

Additional Info



Peak Cutoff Knobs: Two knobs at the top of the panel (Peak A and Peak B) control the individual cutoff

frequency of both sub­filters.

Peak Mod Knobs: Attenuverting controls for the two sub­filters.

Dual Mod Knob: Logarithmic attenuator. controls the cutoff frequency for both sub­filters. Tracking is

approximately .5V/OCT (when turned fully clockwise).Res/Ping Knob: Controls the amount of resonance/damping in both sub­filters.

Curve Knob: Controls the “wave folding” function of the TwinPeak.

LVL/Fade Knob: Function as either a cross­fader or individual level­control for inputs 1 and 2.


1V/O CV: Controls both sub­filters. Tracking is decent, 5 octaves at approx. 1% tolerance.

D­MOD: CV Input for Dual Mod Attenuator.

MOD A: CV Input for Peak A Mod Attenuverter.

MOD B: CV Input for Peak B Mod Attenuverter.

RES CV: Modulates resonance or damping of the filter. Also creates a very nice bandwidth modulation


with manual control at lower settings.