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ULTRACURVE PRO DEQ2496
3.MENU STRUCTURE AND EDITING
Fig. 3.7: Filter curves with signal above/below the threshold
3.2.4 FBD menu
The DEQ2496 features a Feedback Destroyer function, which
corresponds largely to the PEQ menu as far as operation and
choice of parameters are concerned. However, the FBD menu
has some additional functions and therefore comprises three
pages rather than just two.
The Feedback Destroyer allows you to apply heavy attenuation
(no boost) to specific frequency ranges, so as to remove certain
frequencies that are liable to cause feedback. With its extermely
narrow-band filters it hardly affects the overall sound at all.
Fig. 3.8: FBD menu (page 1)
The first page shows a graphic representation of the filters. It
is structured and operated in the same way as the first page in
the PEQ menu. Since this menu can only be used to cut signals,
the 0 dB line is located in the upper part of the display. The
differences here are the settings ranges for the GAIN and
BW(OCT) parameters. In order to achieve extremely narrow-
band filters with high attenuation factors, the bandwidth ranges
from 1/10 to 1/60 oct. and the GAIN from 0 to -60 dB.
+ At least one filter must be activated on page 2 to
be able to access the first page of the FBD menu.
Fig. 3.9: FBD menu (page 2)
Page 2 provides a table showing the ten memory locations
available. If parametric EQs have been activated in the PEQ menu,
these will be shown here too, because the memory locations
are intended for both FBD and PEQ settings.
+ Any parametric EQs activated in the PEQ module
cannot be edited in the Feedback Destroyer menu
(FBD)and vice versa.
In general, you can select two types of feedback filters: SNGL
mode (single shot) and AUTO mode. To be able to identify
feedback frequencies, the Feedback Destroyer splits up the
entire frequency spectrum (20 Hz to 20 kHz) into bands of
1/60 octave and measures their respective levels. The resulting
values are then referenced to the level of the complete signal.
The difference between these levels determines whether a filter
is activated or not. As soon as a filter is set to AUTO or SNGL
mode, the unit automatically tracks feedback frequencies and
assigns the active filters to them.
AUTO mode
Microphones that are moved around during a performance
(e.g. vocal mics) often suffer from varying feedback frequencies
as a result of the changing positions on stage. This kind of
feedback is best suppressed in AUTO mode. A filter in AUTO
mode automatically identifies the optimum parameter settings for
feedback suppression. If the feedback frequencies change, the
AUTO filter can track them and keep suppressing them. It always
selects the respective frequencies and a very narrow-band
filter configuration to affect the wanted signal as little as possible.
When all filters are locked in to a specific frequency, and a
new feedback frequency occurs, then the filter with the oldest
or first feedback frequency detected is released and used for
the new one. If new feedback occurs very close to or even at
an already identified frequency, the parameters of the filter
already in use will be adapted, for example by widening its
bandwidth or raising the amount of signal attenuation.
SNGL mode
Filters in SNGL mode (single shot) also searches feedbacks
automatically. If feedback is identified, the filter parameters are
configured optimally for feedback suppression. Contrary to filters
in AUTO mode, filters in SNGL mode lock in firmly to the identified
frequency (LOCK FBD), however, their width and depth are still
being adapted to changes in the feedback frequencies. The
bandwidth is enlarged, if the feedback frequency shifts slightly,
and the amount of attenuation is raised if feedback persists. To
prevent a feedback frequency from recurring, the amount of
attenuation is not reduced. Thus, SNGL mode is ideally suited to
suppress constant feedback frequencies, as they are typically
produced by fixed or permanently installed microphones.
Use the LOCK FBD function (B key in the left bottom part of the
display) to lock the frequency of the SNGL filter manually
(SNGL Ï). This means that the filter can only be modified in its
bandwidth and amount of attenuation. With UNLOCK FBD
(B key) it can be unlocked again.
Fig. 3.10: FBD menu (page 3)
The third page provides three additional dynamics parameters
for all FBD filters.
SENS (upper data wheel) allows you to determine the point of
onset for feedback suppression (describes the difference
between feedback signal and overall level). When a signal
reaches this difference, it gets reduced in level. The setting
range here is from -3.0 to -9.0 dB. Use THRESHOLD (large data
wheel) to select the threshold from which a certain frequency is
considered to be feedback. The MAX. DEPTH parameter below
determines the maximum attenuation of a filter (-18 to -60 dB) in
6 dB steps, and thus the GAIN setting range as displayed on the
first and second page (lower data wheel).
LEARN MODE is activated with the A key. This function
generates additional short pulses and raises the overall gain to
provoke feedback. Subsequently, the feedback signals arrive at
the input of the DEQ2496, are identified and suppressed. LEARN
MODE is ideal for use before a live event, for example to
automatically configure the SNGL filters (tuning-in of a P.A.
system).
The following symbols inform you about the current status of
the filters:
; In this setting, an AUTO or SNGL filter is on duty (RUN) to
react to the incoming signal and effect the necessary
settings.