ULTRACURVE PRO DEQ2496

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 ∉). 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.

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3.MENU STRUCTURE AND EDITING