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The POWER-Q is the most recent refinement of the patented Sabine FBX technology that allows
the unit to automatically sense and eliminate feedback. The POWER-Q offers two types of FBX
automatic feedback control filters: FIXED and DYNAMIC. FIXED filters provide gain before feed-
back. DYNAMIC filters eliminate transient feedback that comes and goes throughout the program.
Follow the procedures described on pages 9 & 33 to "teach" the FBX automatic feedback control
filters the frequencies and depths necessary to control feedback in your system.
BACKGROUND: The POWER-Q uses a sophisticated algorithm (patented) to monitor the input
signal and detect the onset of feedback. The FBX algorithm is fast, accurate and unique in its
ability to distinguish feedback even when audio signal is present. When feedback occurs, the
algorithm makes a precise determination of the feedback frequency and sets a filter of prescribed
width (typically 0.10 octave, but this can be modified in the GLOBAL PARAMETERS menu) at that
frequency. Initially, the filter is only -3 dB deep, which is often sufficient to eliminate the feedback.
If the same feedback frequency persists, the filter is deepened progressively to a maximum depth
(which is also user-selectable) or until the feedback is eliminated.
FIXED FBX filters are used to eliminate feedback due to characteristics which are unlikely to
change, such as room acoustics and fixed microphone installations. Once a FIXED filter is set, its
center frequency remains fixed, but it may be deepened automatically, if necessary, to control
additional feedback at the same frequency. The POWER-Q gives you the option of locking the
fixed filters so they won't go deeper than the original setting. This feature is especially useful in
unattended PA systems. The third soft key button ("LOCK+/-") locks and unlocks the fixed FBX
filters. The "FBX F" (fixed) filters change to "FBX L" when locked.
DYNAMIC FBX filters are used to deal with transient feedback that comes and goes during a
program. Changes in room acoustics (due to temperature or audience size changes), changes in
gain (musicians almost always play louder during a performance than at sound check) and changes
in mic position (e.g., with a wireless mic) often result in new feedback frequencies arising during
performance. When a new feedback frequency occurs, a new DYNAMIC FBX filter is automatically
assigned to eliminate the feedback. When all of the DYNAMIC filters have been used, the filter that
was set earliest is reassigned to handle subsequent feedback, and so on.
One trait shared by both the FIXED and DYNAMIC FBX filters is their ability to track feedback. We
have already said that DYNAMIC FBX filters will set new filters or recycle old filters to eliminate
feedback and that FIXED FBX filters are not recycled. If, however, the feedback frequency is
detected to be very close to an existing feedback frequency, it is presumed that this new feedback
is the result of a "drift" in the resonating frequency of the original feedback. Drifting can be the
result of changes in air temperature or humidity. In this case, the closest filter will automatically
move slightly to the new frequency to track this feedback. You can adjust the tracking values in the
GLOBAL PARAMETERS menu.
If the P.A. system is moved from the original setup, the POWER-Q must be "retaught" where to
place filters to eliminate feedback. To reset, press the "MORE" button until the option "RESET"
appears next to the second soft key button. Press "RESET," and you will be given the option of
resetting all filters or just the FBX, graphic, or parametric filters for one or both channels. (See the
section on GLOBAL PARAMETERS for more information about controlling FBX automatic feedback
control filters.)
PARAMETRIC FILTERS. If a filter type is set to "PARAM" (parametric), it is possible to edit its
frequency, width and depth by moving to the appropriate field with the arrow keys while in the LIST
mode (press the second soft key button, "LIST/CURVE," until you see a table of filters). You can
set the center frequency of POWER-Q parametric filters anywhere between 20 Hz and 20 KHz with
1 Hz placement resolution. The filter's WIDTH ranges from 9.99 octaves to 0.01 octave. The
DEPTH can be set anywhere from -84 dB cut to +12 dB gain in 1 dB increments. These param-
eters are set using the arrow keys to choose the correct parameter and the data wheel to change
the parameter value.
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