Rev. 5 – Jun 2020 Page 73 of 91
2.3.1 Lock
The Lock circuit is designed to provide a precise but sub-
tle correction of an oscillator’s pitch (the ‘slave’) when it
is very close to an integer multiple or divisor of another
oscillator’s frequency (the ‘master’). It is mainly used to
compensate for slight tracking variations that may occur
when CV controlling more oscillators with the same
V/oct signal.
The Lock system uses the master’s square wave to
slightly change the thresholds of the slave oscillator’s
core: it will shift them up when the master’s waveform is
positive, and down when it is negative. As a result, the
slave oscillator will gently rush and drag to follow the
master’s frequency, without resets or abrupt changes in
the waveform direction.
Since this circuit is designed to correct very small differ-
ences in frequency, we recommend using it mainly when
the slave oscillator is within a semitone from its desired
pitch. If the ratio between the two oscillators is not an
integer number, some changes in the harmonic spectra
may occur.
By default, the green oscillator can be locked to the yel-
low one by moving the three-way Sync Switch (B.16)to the
Lock position.
The yellow oscillator does not have any hardwired slave
capability, but it can be synced to an external waveform
by patching it to the Sync Input (B.17) and setting the back
jumper to Lock.
2.3.2 Flip Sync
It has been said that sometimes an extreme modulation
of the synced oscillator may be deliberately used to create
complex waveforms, as with Hard Sync. BRENSO’s tri-
angle cores allow a different technique, typical of this kind
of oscillator, called Flip Sync (or Reverse Sync): instead of
forcing the slave oscillator’s waveform back to the begin-
ning at every master’s duty cycle, it reverses the wave di-
rection. This translates into a more mellow tone, which
allows creative modulation without hearing the harsh
“spikes” made by the slave oscillator’s waveform reset by
sawtooth-based Hard Sync.
Flip Sync is activated by moving the Sync Switch of the
green oscillator’s section (B.16) to its rightmost position:
when engaged, the green core will invert its waveform di-
rection at every yellow duty cycle.
As we said above, Flip Sync can be activated for the yel-
low oscillator, too, by placing the jumper on the back of
the PCB to the Sync position. In this way, the yellow os-
cillator will become the slave of any signal patched to its
Sync Input (B.17).
This technique, in contrast to Lock, creates dramatic
changes in the slave’s waveform and can be used for more
expressive and creative purposes. Since it is not phase-
based, and since preserving the original waveform is not
a priority, there is no preferred frequency range for
setting the slave oscillator to be synced properly. Of
course, a master frequency higher than the slave one
would result in a change of amplitude, of the slave since
it will not always be possible to reach the full cycle with-
out a change of direction.
3 TIMBRE
So far, we have seen several ways of generating complex
timbres by just acting on the oscillators’ frequencies, but
BRENSO is capable of much more. A whole section is
dedicated to modulating the waveforms of the yellow os-
cillator through a series of circuits. Here is an overview of
the signal routing.
· The yellow triangle wave is routed to a waveshaper
called Triangle Shaper (C.1, C.2, C.3), which morphs be-
tween a sine and a logarithmic wave. The resulting wave-
form is sent to two destinations: a crossfader called Source
(E.1, E.2, E.3), and a comparator for Pulse-Width Modula-
tion (PWM – D.1, D.3, D.4).
· The comparator takes the modulated waveform and
derives a pulse-wave, which can be modulated; alterna-
tively, the Pulse-Width Modulation (PWM) Source can be set
to be the pure triangle wave of the yellow oscillator (D.2).
· The PWM wave is sent to another waveshaper called
Pulse Shaper (D.5, D.6, D.7), which emphasizes the high or
low harmonics. The resulting signal is sent to two desti-
nations, the Source crossfader, and the square wave output
of the yellow oscillator. A switch (A.6) below the jack
socket (A.5) selects the output source: pure square wave,
or shaped-wave.
· The Sources crossfader (E.1, E.2, E.3) receives signals
from the Triangle Shaper and the Square Shaper and blends
them together. The result is fed into a Wavefolder (E.4 to
E.10).
· The Wavefolder further processes the sound, and its
output is sent to another crossfader for amplitude modu-
lation (see below, §4) before being routed to the Final out-
put (A.7).
All the aforementioned waveshaping techniques are
performed over the yellow oscillator’s waveforms, and
their amount can be modulated (even at audio rate) by
the green oscillator’s sine wave, through a circuit called
Modulation Bus (F.1 to F.5). The following paragraphs will
describe the modulation circuits, and the last one will de-
scribe the role of the green oscillator and the Modulation
Bus.
TRIANGLE SHAPER
The first waveform modulation circuit is the Triangle
Shaper (C.1). It can be seen as a three-way mixer that
blends three waveforms: a sine wave (leftmost position),
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