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feedback destroyer Utility Software
Old 12th March 2014
  #61
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Thanks for a topical, if volatile thread, Animal. I have been considering a similar unit for precisely the same reasons.

Is the comment above, that the DriveRack PX is no better than the Behringer unit accurate?

I am interested in pinching transients than can sometimes happen when the room changes, or a microphone is moved unexpectedly.
Old 12th March 2014
  #62
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Quote:
Originally Posted by wesg View Post
I am interested in pinching transients than can sometimes happen when the room changes, or a microphone is moved unexpectedly.
The acoustic conditions of a room/venue (even a small one) can never change fast enough to cause the audio system to feedback, something must be very out of whack.

Same thing if there is feedback just because you move a microphone, (unexpectedly or otherwise) there is a problem. You should be able to walk around the stage with a vocal mic and not have feedback.

The system was probably not setup properly to begin with in both cases and this is not a condition the 'magic' box can solve….
Old 12th March 2014
  #63
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Quote:
Originally Posted by Samc View Post
The acoustic conditions of a room/venue (even a small one) can never change fast enough to cause the audio system to feedback, something must be very out of whack.

Same thing if there is feedback just because you move a microphone, (unexpectedly or otherwise) there is a problem. You should be able to walk around the stage with a vocal mic and not have feedback.

The system was probably not setup properly to begin with in both cases and this is not a condition the 'magic' box can solve….
yeah but if someone opens the door to the smoking area and props it open, whoosh there goes your mix.
Old 12th March 2014
  #64
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SamC, I think you have already made it abundantly clear in previous posts that you hate feedback destroyers and everybody who can't afford to pay a professional sound company to run sound for $100-a-man bar gig.

Unfortunately, horribly terrible incompetent people like me sometimes get into situations where we have transient bits of "ring" pop into our mixes by surprise, especially in difficult small rooms with low ceilings and hard walls.

So, we are exploring solutions. If you have actual solutions to offer, they would be greatly appreciated. Don Boomer, for whom I have a great deal of respect, seems to think that feedback destroyers are useful when quality units are used properly. I would like to learn which units are worth considering, and how to use them effectively.

Stopping a performance so I can starting stabbing at the GEQ is not an option. Never mind that that the problems I normally experience last less than 500ms.

My current solution is to simply turn down the band, but learning about alternatives would be useful.
Old 12th March 2014
  #65
S21
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Quote:
Originally Posted by wesg View Post
Thanks for a topical, if volatile thread, Animal. I have been considering a similar unit for precisely the same reasons.

Is the comment above, that the DriveRack PX is no better than the Behringer unit accurate?

I am interested in pinching transients than can sometimes happen when the room changes, or a microphone is moved unexpectedly.
My view is that the drpx and fbq100 work. Neither provide a magical nirvana.

I didn't give the drpx a good workout. I bought that after the fbq100. By that time I wasn't looking for feedback suppression. I tried the drpx feedback suppression out on a bench and it didn't seem any different to the fbq100. I've never turned it back on since my initial "try everything in the manual" session.

I can do a side-by side test this weekend if there is still interest. Exactly matching levels and position(hence phase) is very hard, so my tests won't be able to be completely scientific.
Old 12th March 2014
  #66
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Quote:
Originally Posted by S21 View Post
I can do a side-by side test this weekend if there is still interest. Exactly matching levels and position(hence phase) is very hard, so my tests won't be able to be completely scientific.
'Y' to two pre amps
Old 12th March 2014
  #67
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FWIW, one size does not fit all. My Sabine Graphi-Q gets its FBX used almost exclusively in corporate AV environs... Small meetings (listening to a Legislation Update regarding my printing industry client as I type... to some, boring... but lucrative... did I mention I'm in Miami on this job?) with untrained and not-time-to-train people requesting lavaliere mics in a room with three different ceiling heights and several rather nasty nodes for feedback.

So... in my corporate meeting sandbox, I set the podium, ring a couple of main freqs (108, 320, 660 here) with narrow channel parametrics... add the WL185... (155, 550, 2.4K)... and the Countryman E6 (465). Then, with all open (worst case scenario) push the master level and set the 5 "locked" 1/10th octave filters on those. That gets me 3-5dB additional GBF than the parametrics alone. Best result: no feedback at a stupid gain level... especially with only one or the other open.

Would any of this work need to sell via "BoringPresentationsonTape.com"? No. Will my clients look elsewhere if we have a constant battle with feedback across three days...? You bet. Will I agree that a FBX properly employed is useless...? Nope.

Different strokes.

BTW... I do kinda the same thing on a rock stage when I'm up there during setup and soundcheck on the M7 or my personal SL24.4.2 running the iPad control apps, identifying obnoxious freqs by ear, notching them, and playing with the Q to get back as much music as possible without the squeals.

MMV... works for me.

HB
Old 13th March 2014
  #68
Registered User
 

Quote:
The acoustic conditions of a room/venue (even a small one) can never change fast enough to cause the audio system to feedback, something must be very out of whack.
From “Experimental Investigation of Sound-System-Room Feedback” by William K Connor.

At times for example, with the system gain just at the point of positive feedback in the live room, it was possible to turn the howlback off and on, as with a switch, by moving a partially open door backward and forward about one inch.

Quote:
Same thing if there is feedback just because you move a microphone, (unexpectedly or otherwise) there is a problem. You should be able to walk around the stage with a vocal mic and not have feedback.
From the same paper, ….added gain before howlback realised at one location through narrow-band equalisation is not likely to be available at another.

Feedback occurs at frequencies where the loop gain is equal to or exceeds unity and the loop phase is an integral multiple of 2 pi radians. If you are operating at a level where the loop gain is well below unity, you should not have feedback problems ( a system with a flat response helps here). With such a system it is as much the skill of the system designer and/or engineer you need to thank as the person doing the mixing.

Where feedback is likely to be a problem, narrow band filters are generally recognised to be the best solution (1/3 octave graphics are not particularly narrow band). Feedback destroyers generaly implement narrow band filters automatically. The problem is in how they recognise feedback. With simple systems if the device is not sensitive enough it takes too long to cut the feedback, too sensitive and you risk cutting sustained notes.

With the advent of spectral editing software such as adx trax, sonicWorx and spectral layers, that can isolate sections of audio based on the spectral content, at some point I suspect we will get feedback destroyers that can out perform humans.
Old 13th March 2014
  #69
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Quote:
Originally Posted by wesg View Post
SamC, I think you have already made it abundantly clear in previous posts that you hate feedback destroyers and everybody who can't afford to pay a professional sound company to run sound for $100-a-man bar gig.
Is this kind of bull**** really necessary….I don't 'hate' anyone or anything, I have offered an alternative solution to relying on those boxes because I believe that anybody who calls himself and audio engineer should at least be able to work around them in any situation….

Quote:
Originally Posted by wesg View Post
My current solution is to simply turn down the band, but learning about alternatives would be useful.
You could start by setting up your system properly and pay special attention to the track(s) that are most likely to feedback. learn to listen for the telltale sounds of an impending feedback and use your headphones to monitor those channels carefully so you can prevent the feedback from occurring in the first place.

There is a relationship between the the distance of the microphone and the sound source (monitor and FOH) and the volume of the sound source. Anytime you go beyond the threshold there will be feedback…science determines that fact. Therefore if you can also get your bandmates to respect the thresholds and not point their microphones in certain directions you might stay out of feedback trouble...You could also turn down a monitor or the FOH.

Just curious, but why would you stop a performance for an instance of feedback that only lasts 500ms?
Old 13th March 2014
  #70
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Quote:
Originally Posted by Electrolytic View Post
yeah but if someone opens the door to the smoking area and props it open, whoosh there goes your mix.
I'd like to think my mixes are a little more robust than that…they can usually survive an open door, and those that don't can't be saved by a feedback destroyer.
Old 13th March 2014
  #71
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Quote:
Originally Posted by hbphotoav View Post
Will I agree that a FBX properly employed is useless...? Nope.
I don't remember anyone suggesting any such thing though...
Old 13th March 2014
  #72
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Quote:
Originally Posted by Steve_B View Post
From “Experimental Investigation of Sound-System-Room Feedback” by William K Connor.

At times for example, with the system gain just at the point of positive feedback in the live room, it was possible to turn the howlback off and on, as with a switch, by moving a partially open door backward and forward about one inch.
My job (or at least part of it is to prevent feedback…not setup experimental situations where feedback is likely to occur.

Quote:
Where feedback is likely to be a problem, narrow band filters are generally recognised to be the best solution (1/3 octave graphics are not particularly narrow band).
I'm advocating for the prevention of feedback…not for the best way to kill it.
Old 13th March 2014
  #73
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Quote:
My job (or at least part of it is to prevent feedback…not setup experimental situations where feedback is likely to occur.
Unless you are designing your own systems from scratch; microphones, mixers, amplifiers, loudspeakers, etc, you can be sure that you are relying on the fact that others have set up experimental situations to enable you to successfully mix bands.

There are quite a number of technical papers written, by well-respected authors, on the subject of the causes and prevention of feedback. The fact it is not your job to set up experimental situations does not diminish the fact that experimental research has shown that what you wrote

Quote:
The acoustic conditions of a room/venue (even a small one) can never change fast enough to cause the audio system to feedback, something must be very out of whack
Is not universally true.

Quote:
Where feedback is likely to be a problem, narrow band filters are generally recognised to be the best solution (1/3 octave graphics are not particularly narrow band).
Quote:
I'm advocating for the prevention of feedback…not for the best way to kill it.
Perhaps I should rephrase what I wrote and say that narrow band filters are generally recognised to be the best solution in preventing feedback. When properly implemented feedback is less likely to be a problem.
Old 13th March 2014
  #74
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Quote:
Originally Posted by Samc View Post
I'd like to think my mixes are a little more robust than that…they can usually survive an open door, and those that don't can't be saved by a feedback destroyer.
you obviously don't work at the coal face, you've got it chusty. I never had feedback from an open door but the sudden temperature differential can send a mix 'west'. Think festival, when the sun goes down and the temp drops, the speed of sound changes and the nodes shift.

Scienced


loving your work as always Steve_B
Old 13th March 2014
  #75
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Quote:
Originally Posted by Samc View Post
The acoustic conditions of a room/venue (even a small one) can never change fast enough to cause the audio system to feedback, something must be very out of whack.

Same thing if there is feedback just because you move a microphone, (unexpectedly or otherwise) there is a problem. You should be able to walk around the stage with a vocal mic and not have feedback.

The system was probably not setup properly to begin with in both cases and this is not a condition the 'magic' box can solve….
So let's look at what causes feedback. Simply put it happens when the sound getting back to the microphones meets or exceeds the level that it went into the mic at the first place. That point is called the "Unity Gain Threshold". But that sound must be in phase or very nearly in phase. And single frequencies that are out of phase will NOT feedback because they cancel.

So when you move a microphone even inches from where you started from the phase of the returning sound changes. Some of it is in phase and some of it is not (comb filtering). You will never get feedback down at the bottom of the "comb" for those frequencies. Now when you set up your system and have "tuned it in" some frequencies were down at the bottom of the comb and so they would have been excluded form consideration. But now when you move a mic the phase will shift again as the distances are now different than they were and now those frequencies could start wailing.
Old 13th March 2014
  #76
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Quote:
Originally Posted by Steve_B View Post
Unless you are designing your own systems from scratch; microphones, mixers, amplifiers, loudspeakers, etc, you can be sure that you are relying on the fact that others have set up experimental situations to enable you to successfully mix bands.

There are quite a number of technical papers written, by well-respected authors, on the subject of the causes and prevention of feedback. The fact it is not your job to set up experimental situations does not diminish the fact that experimental research has shown that what you wrote

Is not universally true
I'm not a debutant learning how to suck eggs. I understand the work that researchers do, my job is different.

I will state categorically that acoustic conditions in a typical venue will not change so drastically that it results in a sudden feedback...especially if the system is setup properly and it's full. Opening a door in a typical venue will/should not cause feedback.

Anybody who disbelieve me can go test it.
Old 13th March 2014
  #77
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Quote:
Originally Posted by Samc View Post
I'm not a debutant learning how to suck eggs. I understand the work that researchers do, my job is different.

I will state categorically that acoustic conditions in a typical venue will not change so drastically that it results in a sudden feedback...especially if the system is setup properly and it's full. Opening a door in a typical venue will/should not cause feedback.

Anybody who disbelieve me can go test it.
What about moving mic placement? Are you saying it does not contribute to sudden feedback? If you are then you would be wrong!
Old 13th March 2014
  #78
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Quote:
Originally Posted by dboomer View Post
So when you move a microphone even inches from where you started from the phase of the returning sound changes. Some of it is in phase and some of it is not (comb filtering). You will never get feedback down at the bottom of the "comb" for those frequencies. Now when you set up your system and have "tuned it in" some frequencies were down at the bottom of the comb and so they would have been excluded form consideration. But now when you move a mic the phase will shift again as the distances are now different than they were and now those frequencies could start wailing.
I know all this and I also know that hundreds of concerts and festivals are mixed in all kinds of venues without feedback problems or feedback killers.

my point is that we should focus on preventing them, not killing them after the fact... If you get feedback just by moving a mic a few inches the system was not setup properly...I understand the theory too but I've seen it done properly thousands of times with no problems.
Old 13th March 2014
  #79
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It is not possible to set up a system correctly for mic placement "A" and mic placement "A plus one foot" at the same time without cutting a big unnecessary hole in both systems

Seeing it thousands of times only means that those systems have never been pushed to the limits which for many users is not the case.

Your history of never having feedback even a single time in your career of doing live sound is certainly not typical.
Old 13th March 2014
  #80
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Quote:
Originally Posted by dboomer View Post
Your history of never having feedback even a single time in your career of doing live sound is certainly not typical.
Despite our disagreement on this topic I seriously thought you were above this kind of snarky bull****.

What is the point you're trying to make anyway?
Old 13th March 2014
  #81
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Quote:
Originally Posted by dboomer View Post
It is not possible to set up a system correctly for mic placement "A" and mic placement "A plus one foot" at the same time without cutting a big unnecessary hole in both systems.
In the world of absolute theory where numbers are never rounded off this might be true. But in the real world...in the practical world, it's done everyday. Good engineers tune their systems and musicians run around the stage (and sometimes the entire venue) without feedback problems.

Your second statement defies response...just curious but are you a live sound mixer?
Old 13th March 2014
  #82
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Sam ... You keep making the point that feedback never happens to you. Maybe you are blessed but I doubt a lot of readers to this forum don't share your experience. While I will agree with you that at megadome shows it is a rare occurrence but at the club level, especially for band carrying their own sound, it is a reasonably frequent problem to overcome. The size of the performing space and the levels required quickly set absolute limits to GBF and they cannot be exceeded, period. However understanding the theory of what is actually happening can be very valuable becoming even more valuable as you approach that limit. There are some pretty simple physics at work that are undeniable. So while I wouldn't expect to have much if any problems playing outdoors in an open field I would expect a difficult time of it if I had a band in a 100 seat club with 10 foot ceilings.

My credentials... I have over 30 years of live mixing experience and thousands of shows ... From small clubs to stadiums. Prior to that 10 years as a pro musician. For the last 10 years I have been working as a manufacturer so I infrequently continue with live shows mostly as an A1/designer.

So where in the world are you? Next time I'm in town I'll buy you a beer.
Old 13th March 2014
  #83
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Quote:
Originally Posted by dboomer View Post
Sam ... You keep making the point that feedback never happens to you. Maybe you are blessed but I doubt a lot of readers to this forum don't share your experience.
I keep making the claim that it is better to prevent feedback than it is to buy a box to kill it after the fact. I have not made the claim that I've 'never' had feedback…that would be a stupid lie, but over the years it become less and less of a concern or problem because of my prevention methods and the quality of the tools (monitors, microphones, etc.) I have available to me.

Quote:
While I will agree with you that at megadome shows it is a rare occurrence but at the club level, especially for band carrying their own sound, it is a reasonably frequent problem to overcome. The size of the performing space and the levels required quickly set absolute limits to GBF and they cannot be exceeded, period.
Part and parcel of being a 'good' engineer is knowing where the limits are and staying within them but making it work. Don't go beyond the threshold and then depend on a little box strapped across the output to 'fix' the mess…that make you a hack. (You in the generic sense…I don't mean you, dboomer)

Most guys here don't understand what it means to be in Asia of Africa with a less than ideal situation but knowing that they have to make it work. Knowing that all the learning and all the years of experience will have to come into play now and you can't fake it because you've got over 100,000 people coming for the show. You can't start a thread on gearslutz to get advise and you can't run out and buy anything.

Quote:
However understanding the theory of what is actually happening can be very valuable becoming even more valuable as you approach that limit. There are some pretty simple physics at work that are undeniable.
This is of course true, and while everybody and his dog can 'parrot' stuff they copied from the internet, if they really understood what it meant in practical terms, really understood the science (in a practical sense) behind what they do, Sabine would sell less of those boxes.

Quote:
So while I wouldn't expect to have much if any problems playing outdoors in an open field I would expect a difficult time of it if I had a band in a 100 seat club with 10 foot ceilings.
You may just need to turn it down…

Quote:
My credentials... I have over 30 years of live mixing experience and thousands of shows ... From small clubs to stadiums. Prior to that 10 years as a pro musician. For the last 10 years I have been working as a manufacturer so I infrequently continue with live shows mostly as an A1/designer.
Impressive.

Quote:
So where in the world are you? Next time I'm in town I'll buy you a beer.
I moved to France years ago but I move a lot and this year I'll visit/work on at least five continents. Currently I'm in Jamaica making records…somebody's actually paying me to be here!!! I'll take you up on the beer offer in exchange for some of the best tasting rum in the world.
Old 14th March 2014
  #84
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My $0.02 worth, the name itself says a lot as these devices don't prevent feedback, they try to 'destroy' or eliminate feedback when it occurs. The more you can do to prevent feedback in the first place, the less these devices have to do and the less the impact on the audio signal. A feedback eliminator should not be the only, much less the first, approach used in addressing feedback and in many situations other efforts can result in sufficient gain before feedback to negate any need for a feedback eliminator. However, where all other efforts do not allow sufficient gain before feedback or where things may change significantly then a feedback eliminator may help.

I think the concern is that rather than trying to understand what causes feedback and how to avoid it, people may believe they can simply add a magic box that will prevent feedback. Instead of taking the time to try to maximize gain before feedback acoustically, they will just throw some electronic 'band aids' at it. What seems important to understand is that feedback eliminators work best when applied after you have already done what else you can to maximize the potential gain before feedback. They supplement such efforts, not replace them or make them unnecessary.
Old 14th March 2014
  #85
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Quote:
Originally Posted by museAV View Post
My $0.02 worth, the name itself says a lot as these devices don't prevent feedback, they try to 'destroy' or eliminate feedback when it occurs. The more you can do to prevent feedback in the first place, the less these devices have to do and the less the impact on the audio signal. A feedback eliminator should not be the only, much less the first, approach used in addressing feedback and in many situations other efforts can result in sufficient gain before feedback to negate any need for a feedback eliminator. However, where all other efforts do not allow sufficient gain before feedback or where things may change significantly then a feedback eliminator may help.

I think the concern is that rather than trying to understand what causes feedback and how to avoid it, people may believe they can simply add a magic box that will prevent feedback. Instead of taking the time to try to maximize gain before feedback acoustically, they will just throw some electronic 'band aids' at it. What seems important to understand is that feedback eliminators work best when applied after you have already done what else you can to maximize the potential gain before feedback. They supplement such efforts, not replace them or make them unnecessary.
Amen...

A feedback preventer...that's the box we need.
Old 15th March 2014
  #86
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Whether they " prevent" or "destroy" feedback depends where you are in time.

The best units are dynamic and being so they don't become active until feedback first occurs. That said they very well may "destroy" feedback before it even becomes audible. You can debate that point if you want. However once they do notch out a feedback at a given frequency they do increase the GBF so in this circumstance they actually are preventing feedback

Whether they should be the first or the only unit depends on the local circumstances and the skill of the operator. Way more common that not unnecessary filters (with reference to feedback generation) are likely in place so it is very typical that frequencies that would not cues feedback have been carved out in the name of feedback prevention. Now if you need to shape the "tone" of a speaker system a FBS is not the correct tool.

As always I'm speaking of the best quality units, used properly and not the poorly designed units.
Old 15th March 2014
  #87
S21
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Quote:
Originally Posted by S21 View Post
My view is that the drpx and fbq100 work. Neither provide a magical nirvana.

I didn't give the drpx a good workout. I bought that after the fbq100. By that time I wasn't looking for feedback suppression. I tried the drpx feedback suppression out on a bench and it didn't seem any different to the fbq100. I've never turned it back on since my initial "try everything in the manual" session.

I can do a side-by side test this weekend if there is still interest. Exactly matching levels and position(hence phase) is very hard, so my tests won't be able to be completely scientific.
Nobody will want to hear this, but I think the behringer fbq100 does a better job than the dbx drpx. There isn't a huge difference.

My setup was wireless mic receiver into drpx, drpx into fbq100, fbq100 into powered speaker. I took turns activating the anti-feedback functions on the two boxes while trying to get the mic as close to the speaker as possible. I also tried swapping the positions of the drpx and fbq100.

The signal was fed in series through both boxes so that the overall audio gain would be constant during a test. Both products had audible feedback before suppression. The behringer seemed to catch feedback faster.



*** This was not a test of the audio quality of the remaining notched signal. ***
Old 15th March 2014
  #88
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Quote:
Originally Posted by dboomer View Post
Whether they " prevent" or "destroy" feedback depends where you are in time.

The best units are dynamic and being so they don't become active until feedback first occurs. That said they very well may "destroy" feedback before it even becomes audible. You can debate that point if you want. However once they do notch out a feedback at a given frequency they do increase the GBF so in this circumstance they actually are preventing feedback
The real, hard fact of the matter is that these units cannot, and do not prevent feedback, they can only stop it after the fact. They can't take preemptive action or anticipate anything. They can only react...doesn't matter how quick they are they're still only reactive.

Are people using them on all open mics or are they just using them across the main L R outputs? Because it would seem that the latter would be less efficient and more destructive. Plus what happens when the synth or guitar player plays some pure tones?
Old 15th March 2014
  #89
S21
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The behringer finds and notches lots more spots "pre ring" than the dbx. The live filter list fills up fast and then gets rolled over. I'm not sure these spots would have developed into feedback based on my experience with the mic and all feedback suppression switched off.
Old 16th March 2014
  #90
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Couple of thoughts:

Strapped across the main outputs, the DRPA and Behringer units are pretty much useless. If you want to place one in, put it either on an insert or on a vocal buss to just affect the vocals.

Bought and sold the DRPA and both flavors of the Behringer; they just weren't really set and forget for us.

ART and Peavey make 31-band EQs that do have lights that show the offending frequency(s), which may be more helpful to be able to quickly grab the offending fader. This assumes that someone is mixing, not playing.

If you're in a band and playing while mixing (that includes me), I'd look at the Sabine individual units. We haven't had issues in a while, but they can be helpful to avoid that sound everyone hates - especially when I'm playing guitar and not just mixing...
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