Doepfer A-121 12dB Multimode VCF - Manual (Page 3)

doepfer System A - 100 VCF 2 A-121
3
3. Basics
Low Pass
The most common type of filter in analogue sound
production is the low-pass, which filters out the higher
parts of the sound spectrum, and lets the lower fre-
quencies pass unchanged. Cut-off frequency f
C
de-
termines the frequency at which this occurs (see Fig.
1).
Fig. 1: Typical response curves of the four filters.
High Pass
The high-pass filter is a precise mirror-image of the
low-pass filter: while it lets frequencies that are higher
than the cut-off frequency f
C
through, it attenuates
frequencies below the cut-off point (see Fig. 1).
Band Pass
In a band-pass filter, both ends of the frequency
spectrum are attenuated (see Fig. 1), and the cut-off
frequency f
C
becomes the mid frequency. It gives
you the ability to highlight a particular frequency band.
Notch
A notch filter is the opposite of a band-pass filter,
letting through the upper and lower end of the fre-
quency spectrum, but rejecting a band in the middle
(see Fig. 1). If the mid-frequency f
C
is modulated by an
LFO, the result sounds very similar to phasing.
fc
Out
Freq.
Out
Freq.
Low Pass High Pass
fc fc Freq. Freq.
Out Out
fc
Band Pass Notch