Problem understanding DEQ feedback destroyer settings

[jswingchun]

I am having trouble understanding what I am doing wrong with the feedback destroyer settings in my DEQ. Of course, the manual was of little help.

To mess around with it last night, I set up my OT12s and pointed a mic at them from across the room. I brought up the level on mic to create feedback to try to get the FBD to catch them. I also tried the Learn feature. I had feedback howling so loud things fell off the wall, but all the DEQ grabbed was one frequency. I can't remember if it did that during the learn attempt or when I was riding the slider to create the feedback myself.

I am running the left side of the DEQ for mains, the right side for monitors. So all of these screen shots are from the left side.

The first pic is page two of the FBD prior to pushing any feedback. It looks to me that all 10 slots are set to Auto and ready to go.

The next pic is page three of the FBD prior to pushing any feedback. Again, it looks to me that all 10 slots are set to Auto and ready to go. I set the SENS and THRESHOLD in about the middle of the scale. I tweaked these settings in both directions and it didn't change the outcome.

photo2.JPG (24.3 KiB) Viewed 4026 times

This is page two of the FBD after generating feedback. You can see it grabbed 3169 Hz @ 3/60 BW and reduced it 12db. Feedback was still squealing at deafening volumes at this point and it happily ignored it.

photo3.jpg (22.92 KiB) Viewed 4026 times

Am I missing something obvious?

Can someone explain to me SENS and THRESHOLD settings from the second page? It seems to me that lower numbers on these settings would make the FBD more likely to see something as feedback. Am I looking at this correctly?

Was something flawed in my test procedure?

[Bill Fitzmaurice]

Am I missing something obvious?

Can someone explain to me SENS and THRESHOLD settings from the second page? It seems to me that lower numbers on these settings would make the FBD more likely to see something as feedback. Am I looking at this correctly?

Was something flawed in my test procedure?

I don't remember which it is but either sens or threshold has to be set at like 20dB. It's in the manual somewhere.

[jswingchun]

I don't remember which it is but either sens or threshold has to be set at like 20dB. It's in the manual somewhere.

I looked through the manual and didn't see anything that said that. It has to be threshold because SENS only goes from 3 to 9. I will try it tonight.

After re-reading the manual again, I think I get what the SENS setting it. If the SENS is set to 6, when a feedback signal reaches 6 db above the level of the rest of the content, then it is considered feedback to act upon. So the SENS number equals db, so a lower number would be the most sensitive.

This is a direct quote from the manual regarding threshold. I have read it over and over and I still don't understand what they are trying to say.

Use THRESHOLD to select the threshold from which a certain frequency is considered to be feedback.

It is the only explanation that is given, and it's obviously not enough for me to understand it.

[Bill Fitzmaurice]

I don't remember which it is but either sens or threshold has to be set at like 20dB. It's in the manual somewhere.

I looked through the manual and didn't see anything that said that. It has to be threshold because SENS only goes from 3 to 9. I will try it tonight.

After re-reading the manual again, I think I get what the SENS setting it. If the SENS is set to 6, when a feedback signal reaches 6 db above the level of the rest of the content, then it is considered feedback to act upon. So the SENS number equals db, so a lower number would be the most sensitive.

This is a direct quote from the manual regarding threshold. I have read it over and over and I still don't understand what they are trying to say.

Use THRESHOLD to select the threshold from which a certain frequency is considered to be feedback.

It is the only explanation that is given, and it's obviously not enough for me to understand it.

Like I said, I don't remember it now, except that I had to set one of those way higher than the default setting for it to work.

[Grant Bunter]

Bill said in a comment a while back in another thread that he didn't find it to be so, but it does say in my manual (my manual is V1.1) just before the screen shot of "FBD2" on page 10, that at least one filter has to be activated in PEQ to access the FBD mode.
The activated filter should be labelled as PARAM, rather than AUTO on FBD2.

I haven't messed with FBD yet. My thought though was, in order to satisfy the criteria, to activate a setting such as 20K -12dB or somesuch.

Other than that, my take on the SENS setting is the closer it is to -3, the more sensitive the action to reduce the level of the offending frequency(ies)...

[jswingchun]

Bill said in a comment a while back in another thread that he didn't find it to be so, but it does say in my manual (my manual is V1.1) just before the screen shot of "FBD2" on page 10, that at least one filter has to be activated in PEQ to access the FBD mode.
The activated filter should be labelled as PARAM, rather than AUTO on FBD2.

Thanks!! This seemed to be the issue. Popped one of the PEQs on and it started finding feedback and shutting it down.

Other than that, my take on the SENS setting is the closer it is to -3, the more sensitive the action to reduce the level of the offending frequency(ies)...

I had pretty much sorted out the SENS setting, and my understanding was the same as yours.

It also seemed like a higher number at the THRESHOLD setting made it more sensitive. I would like an explanation of what that setting does. I think I am going to see if I can find one.

[Grant Bunter]

^ Excellent!

When/If you can find out more about the threshold setting, please share...

[Bill Fitzmaurice]

Threshold is the level where it starts working. If the threshold isn't set right the unit can't tell the difference between feedback and normal signal, so it doesn't do anything.

[jswingchun]

Threshold is the level where it starts working. If the threshold isn't set right the unit can't tell the difference between feedback and normal signal, so it doesn't do anything.

The sensitivity is the difference between the feedback and the normal signal. Maybe threshold is a minimum level of signal (in relation to 0 db not overall signal) it has to read on that feedback before it begins to act on it? You would think a smaller number would make it more sensitive though if that were the case, and I found the opposite to be the case.

[Bill Fitzmaurice]

And that's why I feel that instructions should never be written by engineers, because they assume that you know already how the gear works. They should be written by art majors, then proof read by English majors.

[Bruce Weldy]

They should be written by art majors, then proof read by English majors.

....then edited by a user.

[Harley]

They should be written by art majors, then proof read by English majors.

....then edited by a user.

...after being successfuly interpreted by a 12 year old

[Grant Bunter]

No, the 12 year old would just work it all out.

We would then need to interpret the 12yo's take on the manual...

[jswingchun]

I had a nice back and forth with a tech at Behringer regarding this. He went way above and beyond to answer my questions. I basically asked for an explanation of what the THRESHOLD setting is, then I asked some follow ups. My follow up questions are bolded below, the rest are his words.

Bottom line as I understand it:
SENS - Difference between overall level of content and feedback signal before FBD kicks in
THRESHOLD - Volume level of feedback before FBD kicks in without regard for level of the rest of the content

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The threshold of the feedback destroyer sets the volume at which the feedback destroyer kicks in. The easiest way to explain this would be to use numbers as volume information.

Typically feedback will be louder than the instruments or vocals being sent through the DEQ2496. Let's say the levels of the instruments and vocals are "5". Feedback may jump as high as "10". The threshold control in this case can be set, for example, to engage the feedback destroyer if the feedback frequency reaches "6". This is above the level of the instruments and vocals so that they are not affected, but will clamp down on that frequency once it reaches that specified point.

How do the SENS and THRESHOLD work together, what's the difference?

The SENS and THRESHOLD controls on the DEQ2496 are very similar and can be a bit confusing. I'll try to give you an easier way to understand these.

The SENS (sensitivity) control sets the trigger level. This is in dB below the overall signal level. The range of settings is between -3.0dB (least sensitive) to -9.0dB (most sensitive). If the feedback does not reach this level then no filter will be set.

The THRESHOLD control is a global threshold. Below this level there will be no filter set. This is to prevent the Feedback Destroyer from setting spurious filters when they are not needed. For example, when a child or soprano is singing a long note, or when a guitarist, keyboard player, or flautist plays a long sustain note. The range here is from -40 to 0.

For what it's worth, I rarely change these settings as they have worked well for me in the past with their default settings. In case you have made changes to those settings, the default for SENS is -3.0 and the default for THRESHOLD is -15.0.

If you would like to completely reset the device to its factory settings, power the unit down, press and hold both the COMPARE and MEMORY buttons while you power on the DEQ2496. The display will prompt you to verify if you would like to clear all of the presets. Press the A button to cancel, or B for "OK".

Which end of the range makes the THRESHOLD the most sensitive

The "sensitivity" of the threshold is not something that really applies. This control merely tells the DEQ2496 "if the feedback level gets above where I'm set, engage a filter". At -40 the feedback level would barely register before the filter kicked in, but may also engage filters when you don't want them to. At 0 the feedback level would have to be very high for the filter to engage.

Does a PEQ filter need to be engaged before the FBD will work

A PEQ filter shouldn't have to be set in order for the Feedback Destroyer to work. In fact, you can set the whole thing to AUTO and just let the FBD do its thing without you having to get involved. This is perfect for a situation when the sound engineer is a band member. You can set everything to AUTO, then use the LEARN function to filter any frequencies early on, the the AUTO mode grabs what it needs to during performance.

[Grant Bunter]

Thank you!

Typical, what the manual says is not what the tech says (regarding the PEQ setting)...