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 appli-
cations. 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 ad-
justments ? specifically, control of filter width, the amount of boost
or cut, and the mid-band frequency of the filter. This greater preci-
sion, 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-
matically whenever feedback is detected. Effectively, an FBX filterFig. 7b.
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 ba-
sis, as the need arises. To help distinguish dynamic from fixed filters, consider the ex-
ample 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? Feed-
back 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 abil-
ity to change frequency, a dynamic filter is equivalent to a fixed filter.
7.3.2. Balancing Fixed & Dynamic Filters
Your FBX1200, and each channel of your FBX2400, offer a total of 12 FBX filters (com-
bined fixed and dynamic), which can be used as needed to exterminate feedback. After
years of experience and experimentation, Sabine has settled upon a default balance of 9
fixed and 3 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 FBX1200/FBX2400 will auto-
matically exit SETUP mode (enter READY status) after all fixed filters, and the first dy-
namic 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 dy-
namic 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 affect
music programs slightly. Therefore, the wider setting is generally considered to be ap-
propriate 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 class-
rooms ? anywhere one or multiple microphones are used. 2004 Sabine, Inc.
?
LIT-FBX1224-OP-EN-040504a.pmd - rr9 |
ACEC
