DOEPFER VCF 4 Manual - Page 6
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A-123
VCF 4
24 dB notch filter with voltage control of
middle frequency and bandwidth
The patch in Fig. 3 shows a 24 dB notch filter with
voltage-controlled middle frequency and bandwidth.
Freq.
Audio
A-122
In
CV 1
FCV
A-175
BCV
A-123
CV 1
Fig. 3:
24 dB notch filter with voltage control of
middle frequency and bandwidth.
6
System A - 100
Freq.
CV 2
f
L
Audio
Out
A-138
Freq.
f M
CV 2
Freq.
f H
For this patch, set both f
(H igh Pass A-123) to roughly equal cut-off points
(judging by ear).
Use a control voltage "FCV" to alter the middle fre-
quency f
of the notch filter: f
M
Use a control voltage "BCV" to alter the bandwidth,
which is determined by how far apart the two filters'
cut-off frequencies are.
Inverter, these frequencies f
metrically around the middle frequency (see Fig. 4).
Fig. 4:
Effect of FCV and BCV on the notch filter's
response.
doepfer
(L ow Pass A-122) and f
L
= (f
+ f
) / 2.
M
L
H
Using the A-175 Voltage
and f
are altered sym-
L
H
FCV
BCV
f
Freq.
M
H