Rev. 5 – Jun 2020 Page 70 of 91
1 PHILOSOPHY, DESIGN
AND SIGNAL FLOW
BRENSO is Frap Tools’ primary analog source of ar-
ticulated audio waveforms whose degree of entanglement
can be precisely set by the musician.
Its concept developed from a reflection on the very
meaning of the word ‘complex’, often used to describe
this kind of oscillators after the famous Buchla 259 defi-
nition. Complex comes from the Latin verb plector, liter-
ally meaning ‘to braid’, or ‘to weave.’ The purpose of
BRENSO is to update the usual approach to ‘complex
oscillators’ by offering many threads to be woven to-
gether, rather than a pre-defined plait of controls and
waveforms: this to improve clarity, manageability, and
to offer more sonic options to the artist.
We designed a unique signal flow from scratch, in order
to expand the modulation routing and offer to the musi-
cian more access to the crucial parts of the circuit.
BRENSO’s architecture consists of three main parts:
two oscillators, which can modulate each other’s fre-
quency, a timbre modulation section, dedicated to
waveshaping, PWM and wavefolding, and a final stage of
amplitude modulation. These sections will be described
in the next chapters of this manual: Frequency, Timbre,
and Amplitude.
2 FREQUENCY
BRENSO generates sounds with two oscillators, whose
pitch can be independently regulated. Their frequencies
can modulate each other (linearly and exponentially – the
linear FM is Thru-Zero), or they can be synced (with Flip
Sync or Lock).
OSCILLATORS
The two sound sources are analog, triangle-core oscil-
lators with excellent stability and tracking. The oscillators
are labeled with green and yellow graphics on the front
panel, respectively.
Each oscillator features four outputs for different wave
shapes. The output jacks are located at the top of the
front panel. The green oscillator’s outputs are, from left
to right: sine (A.1), triangle (A.2), square (A.3), and saw-
tooth (A.4); the yellow one’s are sine (A.1), triangle (A.2),
square/shaped square (A.5), plus a Final jack socket (A.7)
that outputs the sine and/or the Shaped Square after
their processing through the Timbre and AM sections.
2.1.1 Fine and Coarse Tuning
The two largest knobs of the front panel (B.1) are the
main control for the two oscillators’ Coarse frequency.
Their range goes from ~27.5Hz to ~7040Hz, as dis-
played by the graphics.
The Fine Frequency knob at the top left of the green oscil-
lator and the top right of the yellow one (B.2) finely ad-
justs the frequency by adding or subtracting >1 semi-
tones.
The green oscillator can work at sub-audio rates as well,
through the Frequency Scale switch (B.5). The graphics
around the main knob display the LFO frequency range
below the audio-rate one: when set in ‘Low’ scale, the
green oscillator goes from ~0.15Hz to ~40Hz, ~176
times slower.
Please note that the oscillators are trimmed to match as
close as possible the usage at audio rate: a consequence
of this is that the green oscillator may not perfectly match
the graphics when used as LFO due to components tol-
erance (see tech specs, p. 89).
A red LED (B.4) visually displays the acoustic beats gen-
erated by the two oscillators’ frequencies.
2.1.2 Coarse Frequency Lock
Sometimes the frequency knobs can be endlessly
tweaked in a creative way during the performance, but
some other times, they just need to do what they were
originally designed for: tuning an oscillator before the
performance, and nothing more. However, especially in
crowded patches, the Frequency knob of an oscillator can
be hit by mistake, causing an unwanted detune and jeop-
ardizing the whole performance – especially when more
than one oscillator is playing polyphonic melodies!
To avoid this unfortunate circumstance, we designed a
digital implementation that can be engaged to prevent
accidental twists of the knobs from detuning the oscilla-
tors: the Coarse Frequency Lock.
It consists of two buttons (B.3), one per each oscillator,
that, when pushed, digitally sample and hold the voltage
of the Coarse Frequency knob (B.1), thus keeping the oscilla-
tor's frequency steady. The two buttons are equipped
with an LED: when the circuit is engaged, they will light
up green or yellow, respectively. From this moment on,
the Coarse Frequency knob will no longer change the fre-
quency when moved, and the oscillator’s pitch will be
changed only through external CV or internal frequency
modulation. To restore the knob’s function, push the but-
ton again: if the Coarse knob has changed position in the
meantime, the oscillator’s coarse frequency will set ac-
cordingly.
Please note that the Fine Frequency knob (B.2) is not af-
fected by the Frequency Lock, and it will always be available
in case a little adjustment is needed (for example, to com-
pensate small detuning in extreme climatic situations).
Please note that the Frequency Lock offers a way to avoid
unintended touches: you still need to warm up your BRENSO
as for any other module before to use it.
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