Passeq Analog Code
®
Plug-in
27
Shelf Filters
A shelf filter increases or decreases the energy of all frequencies
above or below a chosen frequency. Depending upon the direction
of processing one refers to high frequency (HF) or low frequency
(LF) shelf filters. Beginning with the threshold frequency, the fre-
quency band is boosted or cut much like a shelf. The maximum
boost or cut achieved at the point furthest from the threshold fre-
quency. The threshold frequency is usually about 3 dB less (with
the overall increase set to maximum). This gives the typical rising
form of the shelf filter’s response curve.
Peak Filters
A peak filter boosts or cuts a chosen frequency‘s energy with a
maximum amplitude and a definable frequency range around this
frequency with a fall off of up to 3 dB to both sides. The chosen fre-
quency with the maximum amplitude is called center frequency—
it takes place in the middle at the peak of the response curve.
The response curve forms a bell, thus peak filters are also often
referred to as bell filters.
Bandwidth
The width of a frequency range or band is musically defined in
octaves. The technical counterpart to this is the “Quality” of a
filter, and the abbreviated “Q” is the most common value for the
bandwidth of a filter. A high Q value means a narrow bandwidth
while a smaller Q factor corresponds to a wider one:
Bandwidth 2 Octaven: 0.7 Q
Bandwidth 1 1/3 Octaven: 1 Q
Bandwidth 1 Octave: 1.4 Q
Bandwidth 1/2 Octave: 2.8 Q
The Basics of Frequency Filtering
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