Bedienungsanleitung Behringer DEQ2496 (Seite 10 von 22) (Englisch)

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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.

Behringer DEQ2496 Seite 10

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