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Operating Manual - PROTEA SYSTEM II 4.24D Distribution / System Processor
7.4d EQ
The Protea 4.24D EQ section offers full parametric EQ as well as 1st and 2nd order shelving filters on inputs
and outputs. Each input channel has six selectable EQ filters, while each output channel has four selectable EQ filters.
In all cases, each filter is selectable between parametric (PEQ), 1st order Low Shelf (LS1), 2nd order Low Shelf (LS2),
1st order High Shelf (HS1), and 2nd order High Shelf (HS2).
Shelving EQ filters: 1st order fil-
ters use a gentle 6dB per octave slope, while
2nd order filters use a 12dB per octave slope
for a more pronounced boost or cut. All
shelving filters have a boost/cut range of +/-
15dB. Low shelving filters have a frequency
range from 19.7Hz through 2kHz, and the
high shelving filters range from 3.886kHz
through 21.9kHz. Shelving filters are most
useful as broad tone controls to boost or cut
the high end or low end of an audio signal's
frequency content. Because they affect a
wider spectrum of audio, they are not as suit-
able for feedback control as parametric fil-
ters.
Parametric EQ (PEQ): uses peak
filters with the ability to control boost or cut,
frequency center, and bandwidth. Think of
one band of parametric EQ as a single graphic
equalizer fader except that the frequency is
variable, not fixed, and that the bandwidth,
or how "wide" the filter affects the frequency
spectrum at the center frequency, is com-
pletely variable. The smaller the bandwidth,
the less the audio signal on either side of the
frequency center is boost or cut, whereas a
larger "wider" bandwidth produces an audible
change to the overall tone of a signal. Para-
metric filters are best used to hunt down and
eliminate problem feedback frequencies, add
or remove a characteristic "hot spot" from mi-
crophones, or clean up room resonance situ-
ations. It is well worth the time becoming
proficient with parametric EQ filters, as they
offer the best solution to many EQ problems.
Protea 4.24D parametric filters have a boost/cut range of +15dB to -30dB. There is more cut than boost
because one of the more common uses for parametric filters is to dramatically cut, or "notch out", very narrow fre-
quencies (low bandwidth) in order to eliminate system feedback problems.
Every instance of a parametric EQ filter has a center frequency selected. The factory default is 1kHz, but each
filter's center frequency is adjustable from 19.7Hz to 21.9kHz in 1/24 octave steps. Carefully sweeping a narrow
bandwidth filter through a problem feedback area, with just a slight boost, is a quick way to find the exact frequency
causing trouble. Once the offensive frequency has been found, cut the filter's level, and then adjust the bandwidth as
narrow as possible while still eliminating the feedback problem. Bandwidth is adjustable from about 1/64 octave to
four octaves, and the lower the bandwidth, the less audible the filter action will be. Finding the problem frequency is
200Hz
2KHz
20KHz
20Hz
0dB
-10dB
-20dB
+10dB
+20dB
-30dB
4. 24D Parametric Filters
W ide (High) Bandwidth
Narrow (Low) Bandwidth
200Hz
2KHz
20KHz
20Hz
0dB
-10dB
-20dB
+10dB
+20dB
-30dB
Low Shelf
High Shelf
4. 24D Shelving Filters
2nd Order Filter
1st Order Filter
