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Thread: How to get automatic feedback control to work on DEQ2496

  1. #1
    Super User Paul Vannatto's Avatar
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    How to get automatic feedback control to work on DEQ2496

    I have had my UltraCurve DEQ2496 for a few years now, and have never been able to use the automatic feedback control. So I have always had to use the old way of finding the feedback frequency with the RTA and notching that frequency on the graphics equalizer.

    This last weekend I realized that I only had 1.3 version of the firmware and was successful in updating that to 1.4, hoping that would fix the automatic feedback problem. But it didn't.

    I have all the PEQ set to automatic. During yesterday's jamboree, I monitored the graphics screen to see if any notching would occur, but to no avail. Can anyone help me figure out what I'm doing wrong, or what I've missed in setting this up?

    Thanks

    Paul

  2. #2
    Dear Paul,

    Use the steps below for programming the AUTOEQ function of the DEQ2496!

    1. Use an XLR mic cable to connect the ECM8000 reference mic into the RTA/MIC input on the back of the unit.

    2. Press the UTIL key to reach page 1 (GENERAL SETUP), use the upper small jog wheel to select ‘CHANNEL MODE’, then use the large jog wheel to set the MODE to ‘DUAL MONO’. Press the B key to ‘ACCEPT MODE’.

    3. Press the I/O key to access page 1 of the I/O configuration.

    4. Use the big jog wheel to highlight the ‘MAIN IN’ box and press the B key to accept the source.

    5. Press the I/O or PAGE key to enter the I/O page 2 and highlight the ‘WIDTH’ box.

    6. Press the I/O or PAGE key to enter the I/O page 3, use the large jog wheel to highlight ‘RTA/MIC’, and press the B key to highlight the +15v phantom power box (if it isn’t already).

    7. Press the RTA key to go to RTA page 1.

    8. Press the B key (AUTO EQ), and you will enter AEQ page 1.

    9. The DEQ2496 will now request that you edit the target curve. Use the A key to select the ‘LEFT’ channel. With the large and small jog wheels you can adjust the EQ bands to reflect the curve you want to end up with (it can be ‘flat’ – without any adjustment). Press and hold the B key to reset if you feel it’s necessary at some point to restart the curve adjustment.

    10. Press the PAGE key until page 2 (AEQ) is accessed. Highlight ROOM CORRECTION if desired.

    11. Adjust NOISE GAIN with the large jog wheel as desired.

    12. Adjust AUTO EQ to ‘slow’, ‘mid’, or ‘fast’ with the lower small jog wheel for the Auto EQ calculation speed.

    13. Press the PAGE key until page 3 of the AEQ menu is displayed. The GEQ is shown with outlined virtual faders.

    14. Adjust ‘MAX’ with the upper small jog wheel for the desired maximum difference (in gain) between adjacent frequency bands. A suggested starting point would be a value of ‘3’.

    15. Press the A key to START AUTO EQ.

    16. The DEQ2496 will measure the ambient (or room) noise for about 15 seconds.

    17. The DEQ2496 will now produce pink noise at its outputs and will analyze system noise for about 15 seconds. If you get a message that the ‘Pink noise level isn’t high enough’, turn up the pink noise level using the large jog wheel and restart the Auto EQ process or wait until a message appears that it is ‘Starting Auto EQ Process’.

    18. Once the Auto EQ process has begun you can view the ‘progress’ from page 2 (RTA response) or page 3 (Graphic EQ changes). If necessary, the ‘MAX SPAN’ and ‘MAX’ values mentioned above can be changed in real time, so that you can see the Graphic EQ changes.

    19. Let this process run until it appears obvious that the adjustments begin to ‘settle’ (or after about 90 seconds), then press the PAGE key until page 3 appears, and press the B key (DONE) to end the Auto EQ process. The unit will default to RTA pages 1-3.

    20. The DEQ2496 will have created the corrective adjustments to achieve the target curve that you specified earlier in this process. To view the Auto EQ changes, press the GEQ key. The settings will be visible and available for further editing.

    21. Repeat the process for the right channel on the unit.

    Note: In the beginning of the Auto EQ process, the DEQ2496 can be set to ‘STEREO LINK’ mode (in the UTILITY menu) if you wish, so that the Auto EQ settings from one channel will be copied to the other channel.

    Hope this helps!



    Kind Regards,

  3. #3
    Super User Paul Vannatto's Avatar
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    Hi Zac,

    Thanks for that excellent and detailed instructions. It is much better than the manual for setting up the AEQ. I've printed that out and will use it for future events that I have adequate time for ringing out the room (which is rare).

    Unfortunately, that is not what I'm trying to get to work. I would like the Feedback Destroyer function to work. Sorry for wording my question wrong. I use 2 of the Feedback Destroyers (DSP1124) on the monitor feeds and they work wonderfully. I never have to worry about the monitors. But I'd like that same feature on the FOH using the DEQ2496. I always have the ECM8000 plugged into the RTA input. As I mentioned, I've had this setup for a few years now, and have never been successful in making this feature work. Could you help me with this as well?

    Thanks again

    Paul

  4. #4
    Hey Paul!

    There a few different ways to attain your goal. Here are a few ideas I think will help with programming the Feedback Destroy functionality.

    Using the Graphic Equalizer function on the DEQ2496:
    Press the GEQ button to display the GEQ menu.
    Turn the small Upper Data Wheel to select the frequency to work with.
    Turn the small Lower Data Wheel to select the bandwidth you want to affect.
    Turn the Large Data Wheel to adjust the GAIN of the frequency.
    For each control you will see visual feedback from the curve in the middle of the display and the numbers on the right of the display.

    Using the Parametric Equalizer function on the DEQ2496:
    Press the PEQ button several times to display page 1 of the PEQ menu.
    Turn the mall Upper Data Wheel to select the frequency to work with.
    Turn the small Lower Data Wheel to select the bandwidth you want to affect.
    Turn the large Data Wheel to adjust the GAIN of the frequency.
    For each control you will see visual feedback from the curve in the middle of the display and the numbers on the right of the display.


    Here are some other important settings to consider:
    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 get reduced in level. The setting range here is from -3.0 to -9.0 dB. Use the THRESHOLD (large data wheel) to select the threshold from which a certain frequency is considered to be feedback. The MAX. DEPTH paramtere below determines the maximim 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).

    Sens = sensitivity.
    this sets the trigger level (in dB below the overall signal level).
    -9 dB = most sensitive / -3dB = least sensitive
    If the feedback does not reach this level then no filter will be set.

    Threshold = this is the global threshold. Below this level there will be no filter set. This is to prevent the DEQ from setting spurious filters when they are not needed (eg when a child or soprano is "singing" a long note, or when a guitarist / keyboarder / flautist plays a long sustained note).

    In other words - before a filter is set, the level of feedback has to reach (a) the threshold and then (b) the sensitivity level.

    The level has little to do with the actual SPL - this is signal level measured at the input to the unit (ref the v/u meter or signal LEDs). If the unit is connected (eg) on an aux send, then it may be that the SPL is very high because the amps are set to maximum, even though the input level to the DEQ may be relatively low. Solution? increase the input level to the DEQ2496 and use the "gain offset" to bring the signal back down again before it goes to the amps.

    Even if the DEQ is setting the "best filters in the world" - you can't do much for bad mic placement. If you hold the mic right up to the speaker then feedback will continue to occur, regardless of whatever "notching" is taking place in the signal. You will need to get the mic positioning sorted out first before thinking about any feedback elimination.

    Kind Regards,

  5. #5
    Super User Paul Vannatto's Avatar
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    Thanks Zac,

    Yes I think it maybe the sensitivity that I don't have setup correctly. I'm printing this out and will go through all the steps you suggest. The reason why I asked the question is that the feedback destroyer function would never work at all. Yet the 2 DSP1124 worked flawlessly every time.

    I am very aware of bad mic placement, and I can assure you that is taken into consideration. The only event that I have a feedback issue is during a monthly jamboree, which is held in a fairgrounds hall. Unfortunately they have the stage and dance floor situated in the middle of the room facing the short side of the hall. And the accoustics is not the best. Where the real problem begins is when they stop the music and make announcements, talk quietly and expect me to amplify them sufficiently to cover the entire room of 250+ people. That's when I have to squeeze as much gain before feedback as I can. I do shoot the room ahead of time (quickly) to reduce the hall accoustic as best as I can. But a crowd will change that accoustic and that is where I need the feedback destroyer to help me with.

    Thanks again for your excellent explanation. I'm confident this will help me accomplish what I want to do.

    Paul

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