User manual

13User Guide Action Filter 4
EN
MODE - small switch, large pull
Each of the Action Filter 4’s channel houses a high- and lowpass filter with a slope of 24 dB per
octave. As described in section "Up with the lowpass" on page 7, it is circuit-dependent whether
both filters form a bandpass- or a band-reject-filter. With MODE switched to BAND, both filters are
connected in series. In contrast, the NOTCH position offers parallel wiring.
The MODE switch has a larger effect than it may seem at first. By switching between BAND and
NOTCH, the functions of both CUTOFF controls change. Let‘s take a closer look!
FILTER A and FILTER B - where is the high- and lowpass?
While describing high- and lowpass filters, the Action Filter 4 does not show any of these on the
front panel. Previously, we labeled the CUTOFF knobs as High and Low. However, this indicated
their position in the circuit. This sometimes led to misconceptions when changing between BAND-
and NOTCH-modes. Therefore, we changed the knob labels to FILTER A (left) and FILTER B (right)
on the Action Filter 4.
The lters in BAND-MODE
With MODE being set to BAND, FILTER A‘s CUTOFF controls the highpass filter. From here, the
audio signal is routed into FILTER B that is configured as lowpass (see figure "Serial combination of
high- and lowpass filter" on page 9). To hear the full frequency spectrum CUTOFF A needs to be
turned fully left and CUTOFF B fully to the right. Moving the control towards each other narrows
the passing frequency range. Because the high- and lowpass filters both cover the full spectrum, the
audio signal may disappear at certain overlapping CUTOFF settings.
Use the markers on the CUTOFF controls as aid to orientation. The further the distance of the
marks, the wider the passing frequency range - very much like a fan being opened. Conversely,
closing the “fan” will narrow the passing band.