Frap Tools CGM, Manual, Page: 9 / 107

Rev. 7 – Aug 2021 Page 9 of 107
It is nice to point out that in modular synthesis we use
the same two or three principles to take care of every pa-
rameter of the sound design.
2
4
TIMING PULSES
We use CV to distribute information (like pitch, ampli-
tude, timbre) all over our electronic composition.
For example, the information of “C#4” is not enough
to generate a note: it generates just a pitch. To have a
note, we need to give it some timing: when it begins, how
long it lasts, when it ends.
For this kind of information, which is essential to define
any kind of musical event (note, melody, rhythm), we use
a particular kind of CV called
timing pulses
, which are
trigs
and
gates
.
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Trigs and gates are pulses , because they can have only
two values, off and on, and because the transition be-
tween one value and the other is almost immediate. Off is
usually 0 V, on is around 5 V.
The main difference between trigs and gates is that trigs
are very fast voltage bursts that go from 0 to 5 V and im-
mediately (actually, after one or two milliseconds) back to
zero, while gates can stay at 5 V as much as we want.
A trig is thus a timing pulse that defines when a certain
musical event should happen, while a gate is a timing
pulses that tells when such an event should happen, but
also exactly for how long.
Trigs are the kind of pulses that we get out of clock gen-
erators, such as SAPÈL, while gates are generated by
modules such as FALISTRI or USTA, which are more
focused on articulation and dynamics.
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POLARITY
We have said that voltage is a difference in electric po-
tential that causes the current to flow through a circuit.
Such a current can flow through a point in either direc-
tion, depending on the voltage that we apply to the cir-
cuit. A positive voltage will make the current flow in a
direction, and a negative one in the opposite. (0
V will not
have any current flow, and such is the value of the cir-
cuit’s ground .)
In case of alternating current, the voltages are also al-
ternating. If such alternation oscillates above and below
0 V, the voltage would be bipolar . However, there are
cases in which the change in voltage is only positive (or,
more rarely, negative). In such cases, we say that the volt-
age is unipolar .
The most common bipolar voltages are the ones used
for generating audio waveforms, since they need to move
the speaker’s cone back and forth. A unipolar audio
2
On the importance of
parametrical
thinking when approaching analog
sound design, see especially (Strange 1984, 4–5).
signal would make the cone move in one direction only,
with potential damages.
Unipolar voltages are, for example, certain envelopes,
or LFOS, especially the ones used for controlling a pa-
rameter which needs to operate in one direction only,
such as amplifiers (on which see the next chapter).
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AUDIO AND CV PROCESSING
In modular synthesis, we add dynamics and expressive-
ness to our music through signal processing. We use quite
a few concepts, but their combination provides many dif-
ferent results.
The most important element of signal processing is the
control over a signal’s
amplitude
. Amplitude is, roughly,
how loud we perceive the sound, which means how much
the air vibrates, which also means how much our speaker
cones vibrate, which, in turn, means how high is the volt-
age oscillation that we generate with out synthesizer.
Controlling the amplitude of a signal means being able
to define the voltage range of our sound source, which is
bipolar: for example, an amplitude of 5 V means that our
waveform will go from 0 V to 5 V, and then from 0 V to
-5v throughout each cycle. Since there is a difference of
10 V from 5 V to -5 V, we can also say that our signal has
an amplitude of 10 V peak-to-peak (V
pp
), i.e., measured
from the highest to the lowest point of the waveform cycle
(“peaks”).
There is another way of measuring a signal’s amplitude,
and it’s the root-mean-square amplitude (rms). In elec-
tronics, this concept is useful because it expresses the the
value of a periodic signal (like alternating current) as if it
were a constant signal of equal average power (like direct
current).
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It is not necessary to dive too much into this
concept now, but we needed to introduce it because we’ll
refer to V
rms
values in the next section about signal levels.
The circuit that allows us to control the amplitude is
called amplifier: increasing or decreasing the amplifier
value, usually through a knob, increases or decreases the
amplitude of our sound, and eventually brings it to 0 V,
where no sound is passing through the circuit. An ampli-
fier is often capable of increasing a signal’s amplitude,
thus providing a louder sound than the one generated by
our sound source. A circuit that only reduces a signal’s
amplitude is often called attenuator.
Furthermore, amplifiers can also deal with signals that
are not waveforms, such as control voltages. In this case,
amplifiers control the voltage magnitude, and they can
make controls sources and their modulations more or less
effective in a patch.
An amplifier that is we can control through voltage is
called VCA, voltage-controlled amplifier. For example, if
3
(Strange 1984, 51–52, 61–62)
4
(Horowitz 2019, 14)