Parametric Filters And Fbx - SABINE SW71-NDR User Manual

FBX Theory & Practice
Fig. 15b - Constant Q Filter
Sabine Constant Q Filters
It is common to describe a filter's quality factor, or "Q," as the center frequency of the filter divided by the filter width (in Hertz)
measured at the -3dB point. Filters that have the same Q, or width, at the -3dB point regardless of the filter's cut or boost are called
Constant Q filters (see Fig. 15b). Filters that get wider as the filter gets deeper are called Proportional Q filters (see Fig. 15c). Lately,
however, the definition of Constant Q is becoming less distinct. Many equalizer manufacturers claim their equalizers have Constant
Q filters, when in fact they get substantially wider as they get deeper. The only way to know for sure if the filters are truly Constant
Q is to inspect their frequency response curves. Sabine FBX Filters are true Constant Q filters.
Sabine 2.4 GHz Smart Spectrum
nate feedback. A graphic equalizer would need more than 10,000 narrow-
band sliders to be as precise and powerful as your FBX.
As an example of the power of FBX, figure 15b shows test results measured
with a PA set up consisting of a microphone, mixer, FBX Feedback Extermina-
tor®, power amp and two speakers. The system's gain was first raised until
the FBX removed nine feedback points. Next, the FBX was replaced with a
graphic EQ. The EQ was adjusted while the system gain was raised to the
same level achieved with the FBX. The frequency response curves of each
device were then plotted and are compared in figure 15b. Note how much
more of the program (the "good audio") is eliminated using an EQ — whereas
only feedback is eliminated using FBX filters.

15.3. 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 applications. 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 adjustments —
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 equal-
izers.
Nothing, however, is easier to use than an FBX filter, which enjoys the preci-
sion of a parametric filter, yet deploys instantly and automatically 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 fre-
quency band. If you want hands-on control, use the Sabine True Mobility®
Remote Software to change FBX filters to parametrics, and tweak frequency,
width, and depth to your liking.
® Wireless
Fig. 15c - Proportional Filter
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