5
at bass frequencies), by introducing nonlin-
ear saturation into the variable feedback (it
causes specific distortion that is quite often
attributed to “fatness”), or by providing ad-
vanced dynamics processing.
The feedback in Zagrzeb (which is necessary
for satisfying the state variable equation)
is fixed. The resonance is not controlled by
changing the feedback, but by shifting the in-
dividual poles of the transfer function.
We have decided not to compensate for the
increased gain, instead, aiming at a smooth
and natural response up to the clipping point.
The range of resonance is trimmed, though,
so that the clipping point is hardly reached
and is therefore non-intrusive. It is also one of
the reasons Zagrzeb is by design incapable of
self-oscillation.
VOltAGE cOntROl
The two CV inputs at the bottom of the panel
control the cutoff frequency throughout the
entire audio range.
The variable fm 1 input is equipped with an
attenuverter featuring a center detent. Note
that the range of this knob is up to ±0.5V/oct
(in other words: ±2oct/V), which is twice as
wide as the fixed input fm 2 thereby facilitat-
ing extreme sweeps while retaining shallow
modulation near the middle position thanks
to the attenuation curve of the potentiometer.
The fixed input fm 2 is not calibrated, but it
provides fairly accurate tracking at 1V/oct.
stEREO PROcEssinG AnD EffEcts
Besides being able to filter two channels of a
stereo signal with the same characteristics,
Zagrzeb offers additional animation of the
stereo image by introducing subtle changes
to the cutoff frequency. The spread input is
conveniently scaled at 1/10th the sensitivity of
the fm 2 input. 0V at the spread input has no
effect, while positive and negative CV results
in the two stereo filters swinging slightly in
opposite directions.
Patching a mono signal to the left input cre-
ates a pseudo-stereo effect. A special multi-
stage phase shifting network introduces a
slight delay between the left and right out-
puts, thus making a stereo output signal with
a wider image. Please note, the effect is most
noticeable with rich sounds that change over
time and may be less spectacular with a static
VCO waveform.
PAtch iDEAs
It is quite easy to achieve a notch filter re-
sponse, even though Zagrzeb does not offer it
by default. Take the filtered signals from the
high pass 24 outs and invert and mix them
with the low pass 24 outs (in other words,
subtract them). Note: The effect is most pro-
nounced with resonance set to minimum.
When one is willing to use the filter in mono,
an interesting formant filter response can be
achieved by mixing two detuned band pass fil-
ters. Patch a 5-10V CV offset into the spread
jack, mix the outputs of the two band pass
outputs, and set the resonance high.
It is possible to achieve a steep 48dB/oct low
pass or high pass filter response by stacking
two of Zagrzeb’s channels. For a low pass re-
sponse, plug the audio signal into the input of
the left channel, then patch from the left low
pass 24 output to the input of the right chan-
nel, and use the right low pass 24 as the final
output.
AccEssORY
Our Coal Mine black panels are available for
all of Xaoc Devices modules. Sold separately.
Ask your favorite retailer. •
patch
ideas
