Epoch Modular TWINPEAK User Manual

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 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, 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 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 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 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.

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*

!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.!

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

Module Width: 12hp!

Module Depth: 22mm

Current draw: ~35 mA, neg.,
~35 mA, pos. !

designated Peak Cutoff Knobs above them, and to the CV
inputs at the bottom left of the panel. Each of these is
tuned to approximately 1V/O when turned fully in either
direction. Center position is the virtual null, turned
clockwise the knob functions as an attenuator while
turning from center to left inverts the polarity of the CV
signal.

Dual Mod Knob: To the left of the panel, underneath the
Peak A Mod knob, you will find this logarithmic attenuator.
This control allows modulation of the cutoff frequency for
both sub-filters. This is a deeper modulation control (.5V
when fully clockwise) and is ideal for punchy envelope
type effects, as it can cut sizable chunks out of the pass
band and create much more drastic modulation of both
filters.

Res/Ping Knob: This one should be more or less self­explanatory. When turned fully clockwise the filter is at
max resonance and will have the longest ping duration.
As noted, the lower half of the knob (from 8 o’clock to 12)
is particular useful for audio rate signals, while the upper
half is generally designated for pinging the filter. On the
other hand, do not let this stop you from experimenting
beyond these general guidelines, but do know that when
at max resonance, audio rate signals may create
undesirable clipping and distortion, particularly higher
amplitude signals, anything above 12 Volts, peak to peak
(See LVL Fade control below)

Curve Knob: Located below the Dual Mod Attenuator,
this knob controls the “wave folding” function of the
TwinPeak. Turned fully clockwise you will have a low pass
response at the output. In this case, controlling the cutoff
frequency of Peak A (whether manually or via CV) will be
the dominant means of sculpting sounds. However, due
to the “pop” described above—tweaking and modulating
Peak B controls will still be audible, only the
corresponding sub-filter will not accept any signal from the
filter inputs.‡ So this is certainly not your typical low pass
filter, as internal modulations from sub-filter B will still add
accents and nuances to the final output signal. Needless
to say, things stand to get allot more interesting as one
turns this knob to the right and more noticeable changes
emerge within the filter’s response. To get an idea of how
this works, running an audio rate signal into either input,
turn the Curve knob and both manual Peak cutoff controls
fully clockwise and then slowly dial back the curve control
to Low Pass position. You will notice that the output level
and frequency spectrum grow from virtual silence (which
defines the 12db band pass curve) to a gradual increase
in both the volume and frequency spectrum of the sonic
content until you reach the limits that define the low pass
curve This exercise briefly displays the transition between
the two polar responses, however it is in between them
that you will gain access to the broader sonic palette that
this module is capable of producing.

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

!Pulsed!inputs!will!create!only!one!ping!in!this!setting.!

LVL/Fade Knob: This knob can serve as either a cross­fader or individual level-control for inputs 1 and 2. Its
function is quite simple. When a signal is placed in input
1, turning the knob from its fully counter clockwise
position, left to right, will raise the input level to from virtual
null to the max maximum at the opposite end.
Conversely, the level of input 2 is increased by turning the
knob from right to left. When both inputs are used, the
same dynamic applies. The farther the knob is turned
away from either input, the stronger that signal will be in
the Filter’s input mix.

CV CONTROLS

1V/O CV: Controls both sub-filters. Tracking is not
perfect, 5 octaves at 1 or 2% tolerance.

D-MOD: CV Input for Dual Mod Attenuator. Approx.

0.5V/O when fully open.

MOD A: CV Input for Peak A Mod Attenuverter.

MOD B: CV Input for Peak B Mod Attenuverter.

RES CV: Controls the amount of resonance or damping of

the filter. Also creates a very nice bandwidth modulation
effect with manual control at lower settings. This CV
actually merits some additional discussion. It is intended
primarily for use with envelopes, LFOs, sample and holds
or step sequencers. Audio rate signals, aside from being
useless here, are not very pleasing to the ear. Within a
complex patch, this may not be noticeable. But, generally,
use of audio rate signals for modulation will result in what
sounds like bleed-through, although technically it is not,
but that requires a lengthier explanation.

WARRANTY:

Modules come with a one-year warranty for parts and
repair (proof of purchase/invoice required), providing there
are no obvious signs of abuse that would indicate
malfunction is due to "external trauma" or that the user
accidentally reversed the polarity of the power supply.

Please contact us at [e-mail] before
returning an item, as we reserve the right to purchase
shipping through our own accounts to ensure the best
possible price. If you bypass this procedure then you may
be liable for the cost of shipping to us, however, if your
module falls under the warranty, we will still cover the cost
of shipping back to you.