Cosmotronic VPRTEX, Руководство пользователя

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RING MODULATION
Ring modulation happens when there’s two bipolar signals that are multiplied in a four-quadrant
multiplier. A four-quadrant multiplier could be referred to as a biplolar VCA. Where a regular two
quadrant multiplier or VCA (picture 11) attenuates the bipolar input completely when the modulator
is in the negative part of its range (resulting in amplitude modulation) a four-quadrant multiplier
(picture 12) actually inverts the incoming signal when the ‘modulator’ has a negative voltage.
The resulting sound is an interesting mixture of both sources and as the frequencies of the two VCOs
get multiplied sidebands are created. The term sidebands refers to the emergent frequencies of the
ring modulated sound. When using two clean sinewaves to ringmodulate each other (in RM there is no
distinction between carrier and modulator) the frequency of the sidebands can be easily calculated*.
The SINE of VCO1 (normalized) is added to the ringmodulator by the RING MOD slider. At the bottom
position there is no ringmodulation. You can instead use an external VCO (or LFO) by patching it into
the MOD input, breaking the normalization. The slider controls the DEPTH of the ring modulation. With
the slider in the most upper position full range ringmodulation (without amplitude loss or gain) is
achieved with signals from -5V to 5V. You can however send -10V to 10V signals into the MOD input
and this actually amplifies the wave, resulting in some saturation or rounding of the shape.
It’s possible to modulate the DEPTH, increasing the sonic options of VORTEX even more. The SINE of
VCO1 is normalized to the DEPTH modulation and the knob is an attenuator for this modulation. You
can break the normalization by patching a signal into the DEPTH input. This input accepts bipolar
signals. The knob is an attenuator for this external modulation. The maximum range of the DEPTH
modulation is achieved with signals from -5V to 5V.
* The frequencies of the sidebands are calculated by adding and subtracting the
frequencies of the oscillations that are being multiplied in the four quadrant multiplier.
When combining a 100Hz and a 300Hz pure sinewave the resulting sidebands will have a
frequency of 400Hz (300hz + 100Hz) and 200Hz (300Hz-100Hz). The base frequencies
of the original oscillations are lost (unless you ringmodulate two frequencies that are
exactly one octave apart from each other).
VORTEX / Complex Oscillator 13
CARRIER
vo
lt -
-
-
+
+
0 0
+
X
O
S
C
IL
L
A
T
O
R
OSCILLATOR
vo
lt -
-
-
+
+
- +
+
X
M
O
D
U
L
A
T
O
R
picture 11: two quadrant multiplier picture 12: four quadrant multiplier