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7.3. Parametric Filters and FBX
Of course, many savvy sound engineers, realizing the limitations of
graphic equalizers in removing problem feedback, prefer to use a
different type of equalizer, called a parametric EQ, for such applica
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tions. If you’re one such audio engineer, you’ll be comforted to know
that FBX filters share much in common with parametrics.
Compared to graphic filters, parametrics allow more precise adjust
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ments — specifically, control of filter width, the amount of boost or
cut, and the mid-band frequency of the filter. This greater precision,
however, comes at a price, as parametric filters are not nearly as
intuitive or simple to use as graphic equalizers.
Nothing, however, is easier to use than an FBX filter, which enjoys
the precision of a parametric filter, yet deploys instantly and auto
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matically whenever feedback is detected. Effectively, an FBX filter is
a parametric filter set to a tenth-octave width, restricted to cut-only
activity, and automatic in its choice of frequency band.
7.3.1. Dynamic FBX Filters
Dynamic FBX filters also set automatically, but can change frequency, on a rotating basis,
as the need arises. To help distinguish dynamic from fixed filters, consider the example
of a speaker using a wireless lavalier microphone, who walks under a ceiling speaker for
the first time. In so doing, he enters a location-specific feedback zone, where it’s possible
that a problem frequency may have escaped detection and notching by a fixed filter. If
all fixed filters have been deployed, a dynamic filter will be set automatically as soon as
feedback appears, solving the problem. Great! But what happens when the speaker then
moves away from the ceiling speaker, and close to a floor monitor? Feedback from the
ceiling speaker is no longer a problem, but a new frequency starts to squeal. If all fixed
and dynamic FBX filters are already set, a dynamic filter will change, to adjust to the new
location. An FBX dynamic filter thus stands guard if new problem feedback arises after
all available filters have been set, providing a deeper and more flexible level of protection
against the dreaded surprise of feedback. Other than the ability to change frequency, a
dynamic filter is equivalent to a fixed filter.
7.3.2. Balancing Fixed & Dynamic Filters
Each channel of your FBX2410 offers a total of 12
FBX filters (combined fixed and dy
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namic), which can be used as needed to exterminate feedback. After years of experience
and experimentation, Sabine has settled upon a default balance of 10 fixed and 4 dynamic
filters, set at the factory. This default condition can be changed to any combination you
require.
If you follow setup instructions for setting FBX filters, your FBX2410 will automatically
exit SETUP mode (enter READY status) after all fixed filters, and the first dynamic filter,
have set. In the default condition, this means you will have set ten filters (nine fixed and
one dynamic), with two dynamic filters still not set and remaining on standby alert. If you
wish to set fewer filters, press the READY button before SETUP automatically exits, after
you have set enough filters to safely achieve your desired gain level. In that case, in the
factory default condition, you will reserve three available dynamic filters for standby.
7.3.3. FBX Filter width
Sabine’s experience and testing with filters and sound quality alone led us to decide
upon a default FBX filter width of .10 (one-tenth) octave as the optimal notch width, able
to eliminate feedback without affecting music programs. If, with all filters properly set,
feedback is still a problem, FBX filters may be set to .20 (one-fifth) octave width. This
wider filter setting will help to better eliminate feedback trouble areas, but may also af
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fect music programs slightly. Therefore, the wider setting is generally considered to be
appropriate where speech (less demanding than music) is the primary application. You
can globally change FBX filter width by pressing the FIFTH button on the front panel.
The width of any set filter will always be determined by the position of the switch at the
time the filter is created.
7.3.4. who Benefits from FBX?
Virtually every sound system will be improved with the Sabine feedback control. Singers
and speakers who do not have sound technicians can now increase their monitor or house
system volume so they can hear themselves clearly and with full fidelity, without worrying
if their microphones will suddenly squeal if they move to the wrong place.
Auditoriums and churches of all sizes will enjoy reliable feedback control. Hotels and
conference centers around the world can offer meeting rooms with microphones that won’t
howl during programs. Sabine FBX systems can be installed in theaters, schools, sports
arenas, courtrooms, teleconferencing rooms, intercoms or interactive remote classrooms
— anywhere one or multiple microphones are used.
Fig. 7b.