Doepfer A-100(~ 40 MB) - Manual (Page 13)

doepfer System A - 100 3. A-100 signal flow
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3. Signal flow in the A-100
3.1 The Principles of Voltage Control
What makes analogue synthesizers (and modular sy-
stems in particular) special is that the important para-
meters of the sound sources (e.g. VCO) and modifiers
(VCF, VCA, etc.) can be altered not just by hand, but
by
voltage control.
This principle was turned into reality by the “father of
the analogue synthesizer”, Robert Moog, who produ-
ced the first commercially available synthesizer in the
sixties. It gives vast flexibility and the potential to make
sounds that have never been made before.
Fig. 5 shows the principle of voltage control, with
examples of control voltages affecting a filter (VCF)
and an oscillator (VCO).
In the case of the VCF, the parameter which is being
voltage-controlled is the Cut-Off Frequency f
c
. The
amount of control voltage input present changes the
cut-off frequency, and thus the frequency of the signal
that the VCF lets through - see the shaded area in the
diagram.
Fig. 5: The principles of voltage control
In the case of the VCO, it’s the pitch which is control-
led by a voltage: an increase of 1 volt corresponds to
an increase of one octave in the pitch.
With a sudden change of voltage, the pitch changes
suddenly, while with a smoother, continuous change,
portamento is created.
f
c
Low Pass Filt er
Input Output
CV Input
CV
Pit ch
VCO
Output
CV Input
Out
Freq . Freq.
f c f c
CV
t t