FXpansion BFD2 Manual - Manual (Page 168)

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Filter Mod
This is a state-variable self-oscillating multimode filter with a response of 12 db per octave.
It has a built-in envelope follower to modulate the filter’s cutoff frequency relative to the
input. This stage is modelled on an analog full-wave rectified envelope follower.
Additionally, the filter frequency can be modulated at audio rate by the input.
The filter is modelled on classic multimode synthesizer filter designs at the circuit level, with
its sound characteristic reminiscent of the well-known Oberheim filter (although it is not an
exact model of this filter).
You can also use the channel’s sidechain input as the source for the envelope follower and
for the audio rate FM. For example you could use a bass drum tuned very low as a rough
and ready LFO to modulate the filter.
Mode
4 filter modes are available, each offering different filtering functions relative to the cutoff frequency.
Low pass
Allows through only frequencies below the cutoff frequency.
High pass
Allows through only frequencies above the cutoff frequency.
Band Pass
Allows through only a band of frequencies around the cutoff frequency.
Notch
This is the opposite of a band pass, in that it allows through all other frequencies except a band of frequencies around the cutoff
frequency.
Modulating a notch filter can give phaser-like results.
In drive
This control sets the amount of signal gain before the non-linearities of the filter. As well as increasing the gain, using more drive
results in a rich and complex interaction with the filter’s resonance.
Out drive
This is an OTA-type non-linear amp function at the output, in order to boost and colour the filtered signal.
Pitch
This control adjusts the cutoff frequency of the filter. It is measured in octaves to be more musically relevant.
Res
This control adjusts the resonance of the filter. You can think of this as having a similar effect as the Gain control on an EQ – it
accentuates the frequencies around the cutoff point.
This is achieved by feeding some of the sound at the cutoff point back into the filter. High resonance settings cause the filter to
self-oscillate – be very careful with your speakers and your ears when using such settings.
Attack
This control changes how quickly the envelope follower section responds to transients in the input signal. Longer attack times
mean that the filter takes a longer time to respond to amplitude changes.
Release
The Release control changes how quickly the envelope follower causes the filter to return to its original position when the input
signal decreases after a transient.
Env Depth
This control adjusts the amount of modulation of the filter’s cutoff frequency by the built-in envelope follower.
FM Depth
This control sets the amount of audio-rate modulation of the cutoff frequency by the input.