Rev. 5 – Jun 2020 Page 71 of 91
2.1.3 V/oct and Integrator
The frequency of each oscillator can be externally con-
trolled through dedicated V/oct inputs (B.13): an external
voltage patched to these inputs will offset the frequency
set by the Coarse and Fine Frequency knobs (B.1 and B.2).
Excellent tracking is guaranteed over more than 6 oc-
taves: this feature provides not only good intonation for
particularly spread melodic lines but also a more precise
ratio between the two oscillators, which translates into
richer and better harmonics when any modulation be-
tween them is engaged, especially frequency modulation,
which will be discussed in the next chapter.
The two oscillators can be independently controlled
with different voltages. However, it is also possible to ap-
ply the same CV to both oscillators by patching it to the
yellow V/oct input and routing it to the green oscillator
through the V/oct Integrator (B.14), without further patch-
ing.
This circuit applies the same CV patched into the yel-
low CV input to the green oscillator after a linear inte-
gration, whose amount is set by the knob position (B.14).
When the Integrator knob is at its leftmost position, the
green oscillator is not affected by the yellow CV, because
it would take an infinite time to reach the target voltage.
When the integrator knob is at its rightmost position, the
exact same voltage offset of the yellow oscillator is applied
to the green one, with a very fast integration. When the
knob is set to any other position, a time lag, similar to a
glide effect, is applied to the voltage routed to the green
oscillator: on the left, the glide effect will be longer, and it
will be increasingly short as the knob is rotated clockwise.
Please remember that the CV is always the same: the only
difference is the time required for the green oscillator to
reach the value.
It is possible to combine the voltage routed through the
V/oct Integrator with another offset applied to the green
V/oct input: for example, the two oscillators can be used
in unison and controlled with the same CV through the
integrator, while an n+1 voltage coming from SAPÈL is
patched to the green V/oct Input to randomly shift the
green oscillator one or more octaves higher.
Furthermore, it is also possible to modulate the integra-
tion time with external CV through the V/oct Integrator CV
Input (B.15): in this case, any external voltage will be
summed to or subtracted from the current position of the
knob.
FREQUENCY MODULATION
The two oscillators of the BRENSO can be frequency-
modulated, even at an audio rate. Such modulation can
be linear or exponential (or both at the same time). You
can use external sources to modulate the oscillators’ fre-
quency, but every oscillator’s input is semi-normalled to
the other oscillator’s sine wave.
When an oscillator’s frequency is modulated at a sub-
audio rate, this generates noticeable fluctuations of the
pitch, similar to a vibrato effect.
When the modulating signal runs at audio rate, the hu-
man ear can no longer perceive the fluctuations: instead,
the result of audio-rate frequency modulation (FM) is a more
complex sound whose timbre is a result of the interaction
of the two frequencies (the one of the oscillator being
modulated, which is usually called ‘carrier’, and the one
of the ‘modulator’).
The change in timbre is due to the generation of other
frequencies, called ‘sidebands,’ which are the sums and
the difference of the carrier and the integer multiples of
the modulator. If the ratio of the carrier frequency and
the modulating frequency is an integer number, such as
3:1, the sidebands generated by FM will be harmonic,
i.e., they will be integer multiples of the carrier and mod-
ulating frequencies. If the ratio is expressed by a non-in-
teger number, the sidebands will be inharmonic, i.e.,
non-integer multiples of the carrier and modulating fre-
quencies. This latter circumstance produces the bell-like
sounds often associated with this technique.
FM in the analog domain is often an approximate pro-
cess, because of the difficulty for the analog components
to guarantee a precise ratio between carrier and modula-
tor frequencies.
The number and amplitude of sidebands is propor-
tional to the amount of modulation that is applied to the
carrier, which is often called ‘deviation’: this value defines
the difference between the carrier’s frequency and the
higher or lower frequency that it reaches when modu-
lated. The more deviation, the wider will be the fluctua-
tions of the carrier frequency, and the greater the number
of sidebands.
The relation between the deviation and the modulator’s
frequency, both expressed in Hz, defines the FM Index.
(For example, if the modulator’s frequency is 200Hz and
the deviation is 400Hz, the FM index would be
400/200=2.)
BRENSO allows you to control the FM deviation, not the In-
dex: the reason is that the deviation is expressed in Hz, so its
impact over the carrier’s frequency will become exponen-
tially lower as the latter increases. This generates sounds that
are rich in harmonics in the low and mid range, without be-
coming excessively harsh in the highest range (See §2.2.1).
Depending on how the modulation is applied to the car-
rier signal, FM can be exponential or linear. Linear FM
modulates the carrier on the basis of the frequency: in
other words, in linear FM, the modulator increases and
decreases the carrier frequency by the same Hz value, ac-
cording to the modulation amount. Exponential FM
modulates the carrier on the basis of its frequency, i.e.,
with intervals: a symmetric bipolar signal will thus in-
crease and decrease the carrier frequency by the same
To Next Page
Loading...