Rev. 5 – Jun 2020 Page 75 of 91
Square Shaper. Both are further modulated through a
Wavefolder.
3.3.1 Sources
The first stage of the wavefolding circuit is the Source
control. It is essentially a crossfader between the two
waveshaped signals: the one from the Triangle Shaper and
the other from the PWM through the Square Shaper.
When its knob (E.1) is set at the leftmost position, only
the signal coming from the Triangle Shaper is sent to the
Wavefolder. Rotate the knob clockwise to blend in the sig-
nal coming from the Square Shaper: at noon, the blend
will be 50-50. At the rightmost position, however, the sig-
nal sent to the waveshaper will not be purely the one com-
ing from the Square Shaper, but a small amount of the
other one will still be audible.
This design choice has been made to improve the tonal
characteristics of the folded signal. Because of its nature,
any “pure” pulse waveform may produce some irrelevant
results wen folded, or even some amplitude loss. To pre-
vent this from happening, the Source control will always
retain some of the triangle-shaped signal, which will dra-
matically improve the behavior of the wavefolder.
If you want to hear the pure sound of the Pulse Shaper,
you can always use the Square/Shaped Pulse Output (A.5)
and set its Source switch (A.6) to the leftmost position.
It is possible to control this parameter, even at audio
rate, by patching an external signal to the CV input (E.2).
An attenuator (E.3) allows for precise scaling of the incom-
ing signal. By default, the modulation input is semi-nor-
malled to the Modulation Bus output (F.2).
3.3.2 Folding
A wavefolder is a circuit that amplifies a waveform be-
yond a pre-determined threshold: for this reason, it can
also be classified as a distortion unit. Once its peaks reach
the threshold (both on the positive and negative sides), in-
stead of being clipped, they are “folded” on themselves.
When they reach the opposite threshold, they are folded
back again, and the cycle repeats, generating a number
of folds which depends on the circuit design. The result
of these folds is an increasing number of overtones that
generate a richer sound.
The main control of BRENSO’s wavefolder is the
Wavefolder knob (E.4). Its range is divided into six layout
graphic portions with increasing line thickness, which
roughly reflect the number of folds performed by the cir-
cuit.
The first section is marked with a dotted line and spans
from the leftmost position to the icon of a “clean” wave-
form. In this range, the knob simply controls the ampli-
tude of the incoming signal, from 0 to unity gain.
Rotating the knob from this point onward will generate
more and more folds, until the maximum is reached, at
the rightmost position.
It is possible to control this parameter, even at audio
rate, by patching an external signal to the CV input (E.5).
An Attenuator (E.6) allows for precise scaling of the incom-
ing signal. By default, the modulation input is semi-nor-
malled to the Modulation Bus Output (F.2).
3.3.3 Symmetry
A peculiar feature of a wavefolding circuit is that it can
be forced to fold the positive half-cycle before the nega-
tive one, and vice versa, by adding a voltage bias to the
incoming signal. This translates into an unbalanced dis-
tortion, which provides different overtone configurations.
This technique can be performed on BRENSO
through the Symmetry knob (E.9): at noon, the incoming
waveform is perfectly balanced. Rotate the knob clock-
wise to increase the folds of the positive half-cycle, and
counterclockwise to increase the folds on the negative
half-cycle.
A CV Input (E.10) sums any external voltage to the value
selected by the knob.
3.3.4 Ping
In many natural sounds, a higher amplitude sound of-
ten contains a higher number of harmonics in the sound
spectra. Moreover, many natural instruments have a
higher amplitude when they begin to generate a note,
which gradually decays over time. The consequence of
these two facts is that the timbre of many acoustic musical
instruments evolves while a note is played, having richer
harmonic content during the attack than during the de-
cay. In other words, the harmonic content is often
vaguely proportional to the amplitude of the signal: think,
for example, about guitar strings, whose tone changes ac-
cording to the strength it is plucked with.
This peculiarity contributes to the dynamic range of
any musical instrument, and it is often an issue with elec-
tronically generated waveforms, whose harmonic content
remains the same throughout different amplitudes.
The wavefolder circuit can be very helpful for changing
the harmonic content over time and achieve more dy-
namic results, and, for this reason, BRENSO is equipped
with a circuit specifically designed to dynamically change
the fold numbers over time by responding to an external
impulse.
The Ping circuit uses an external trig patched to its input
(E.7) to excite the wavefolder, then integrates it with a
nonlinear decay curve. The result is that the folder, once
excited, quickly opens the wavefolder circuit above its
maximum value, and then gradually closes it to the level
set by the Wavefolder knob (E.4). The amount of this decay
is set through the Ping Decay knob (E.8): at its leftmost po-
sition, it is extremely fast, while at its rightmost position,
it becomes significantly longer.
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