Soundtoys FilterFreak - Manual (Page 23)

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HPF – Highpass Filter
The H Hiig gh h P Pa as ss s shape is the exact opposite of the Lowpass shape and works in
reverse; it passes the harmonics in the sound above the frequency setting and atten-
uates and removes the harmonics that are below the frequency setting. A highpass
filter is useful in removing the bass from a sound etc.
BRF – Band Reject or Notch Filter
The B Ba an nd d R Re ejje ec ctt or N No ottc ch h F Fiilltte err is also the opposite of a band pass filter and passes
all the harmonics in the sound but attenuates the band of harmonics near the filters
frequency setting. The “width” of the notch determines how many of the harmonics
near the frequency are removed. The Resonance knob controls how wide or narrow
this band is; the lower the resonance the wider the notch, the higher the resonance
the thinner the notch. In addition to the Resonance knob, the Poles knob also affects
how the filter responds as described below.
Poles
The P Po olle es s knob and associated setting determines how strongly the filter will “filter
out” and affect the harmonics either above or below the frequency set by the
Frequency knob. This is also referred to as how “steep” the filter is. This function is
measured and displayed in “dB” with each Pole equal to a change of 6 dB. The gain
reduction of 6 dB is referring to the gain of harmonics that are one octave away
from the cutoff frequency. So in a 1 Pole LP filter the harmonics one octave above
the cutoff frequency will be lowered by 6dB. Additionally, filter Poles usually come in
pairs, i.e. 2, 4, 6, and 8 Pole etc. The more poles there are, the greater the attenua-
tion of the harmonics that are one octave above or below the setting of the
Frequency knob (depending on the type of filter).
The lower the number of Poles the more gentle (less-steep) the filter’s slope will be
with the effect being more subtle and “smooth”. The higher the Pole setting the
steeper the filters slope will be with the effect being more pronounced. The most
common filters are 2 or 4 poles with have 12 and 24dB slopes respectively.
However, having a filter with 6 or 8 poles is really cool as the effect can be mucho
pronounced. Of course FilterFreak offers you this option for more extreme filtering
affects. Just to clarify all this babble above, here is a list of the Pole settings and the
associated slope of the filters…
2 poles = 12 dB / octave (harmonics one octave from the Frequency are lowered by 12dB)
4 poles = 24 dB / octave (harmonics one octave from the Frequency are lowered by 24dB)
6 poles = 36 dB / octave (harmonics one octave from the Frequency are lowered by 36dB)
8 poles = 48 dB / octave (harmonics one octave from the Frequency are lowered by 48dB)
Note: At lower pole settings FilterFreak doesn’t have to work quite as hard and will
not use as much CPU power!