Doepfer A-100(~ 40 MB) - Manual (Page 125)

doepfer System A - 100 6/12/24/48 dB Low Pass A-108
3
3. Controls
1 Freq.
Control 1 is used to adjust the filter frequency manu-
ally, i.e. the middle frequency f
M
for the band pass
resp. the cut-off frequency f
C
for the low pass (see
fig. 1).
H The actual filter frequency results from the sum
of the manual control 1 and the external control
inputs CV1 ... CV3.
2 CV 2 • 3 CV 3
For voltage control or modulation of the cut-off fre-
quency the CV inputs § can be used. The controls 2
and 3 act as attenuators for the inputs CV2 and CV3
to adjust the control voltage level.
4 Audio Level
This attenuator is used to control the amount of signal
entering the filter audio input !. If the filter’s output
distorts, turn this control down, unless you deliberately
want the distorted sound as a special effect. The filter
audio input is very sensitive so that distortion is possi-
ble even with normal A-100 levels. Distortion appears
about from position 5 with normal A-100 audio levels.
Fig. 1: Frequency response of band and low pass
5 Emph.
Control 3 is used to adjust the filter’s resonance (or
emphasis) - the parameter which emphasises the fre-
quencies around the cut-off point f
C
. For the band pass
this control changes the bandwidth (see Fig.1-4).
Close to its maximum setting, the filter becomes so
resonant that it goes into self-oscillation, and starts
behaving like a sine wave. You can take advantage
of this effect, and use the VCF as an additional sine
oscillator. Self oscillation will break off at high distortion
levels as the internal feedback signal is drown out by
the distorted audio signal. This feature may intentio-
nally be used to create new sounds. If you want to use
the filter as a sine wave oscillator no audio signal
should be fed in (or control 4 to zero).
Freq.
Freq.
Out
Freq.
Emph.
Freq.
Emph.
Out
f
C
f
M