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Author Topic: Where to patch feedback eliminator?  (Read 7225 times)

info@travelingmonkeysound.com

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Re: Where to patch feedback eliminator?
« Reply #10 on: December 15, 2011, 06:05:20 pm »

So... how does a feedback destroyer know the difference between feedback (a "continuous, single frequency event" that may be produced by interaction between loudspeakers and microphones) and an extended musical note (a "continuous, single frequency event" that may be produced by some instruments)?

It does not know the difference. It just depends on how much thought they built into the algorithms. And how lucky you are that day. Your average musical note has a harmonic structure that may or may not differ from it's internal definition of feedback, there are no guarantees.
 
The only way I've seen these devices work "well" (very loosely) is to nab the first couple of troublesome frequencies and then lock the unit down. Not completely terrible for a quick setup in a bad room, and possibly less destructive than a several bands of graphic eq. But if there is a live mode active you can be sure that in the middle of a solo it will start grabbing unintended frequencies.
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Marcus Wilson

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Re: Where to patch feedback eliminator?
« Reply #11 on: December 15, 2011, 09:31:32 pm »

It does not know the difference. It just depends on how much thought they built into the algorithms. And how lucky you are that day. Your average musical note has a harmonic structure that may or may not differ from it's internal definition of feedback, there are no guarantees.
 
The only way I've seen these devices work "well" (very loosely) is to nab the first couple of troublesome frequencies and then lock the unit down. Not completely terrible for a quick setup in a bad room, and possibly less destructive than a several bands of graphic eq. But if there is a live mode active you can be sure that in the middle of a solo it will start grabbing unintended frequencies.

I agree with Nils about the usefulness or otherwise of FBQ units, but wasn't going to go there because Dave already has one.   The last thing I ever want in a sound system is a unit with almost no intelligence tweaking around with the EQ!  If a human started doing that, it could incite me to violence!

Dave, your questions about mixer and amplifier levels are a common issue of gain structure in a sound system.  I suggest you look for a book on sound system implimentation, or suitable internet information, or look at other parts of this forum, to find information on gain structure.

From your posts, you seem to be keen on getting good results and want to learn.  Perhaps you may want to get training from Syn Aud Con or some other training organisation which is well regarded in the industry.   I can't really recommend anything near you because I live in New Zealand.

I don't mean any offence, I have been in the pro-audio industry for 30 years and still actively engage in learning.   My books on audio alone take up about 6 feet of shelf space.

rgds, M
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rgds, M.

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g'bye, Dick Rees

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Re: Where to patch feedback eliminator?
« Reply #12 on: December 15, 2011, 10:04:13 pm »


I'll see what I can do about installing a graphic.  Makes a lot of sense.


I have several church systems I've set up where the operators are either all volunteers with very little actual knowledge/experience or it's a "turn on one switch and go" system.  Both have multi-function processors which include the basic control functions of graphic EQ, parametric EQ and limiting.  I can set access levels for all the functions so that the total noobs can't adjust anything at all, those with some experience and the need to adjust the GEQ can access it with a personal password and so on.

Everyone who uses the system should understand the on/off sequence, how to properly adjust input gain and how to coil cables so they'll last.  I use a sequenced power supply wherever possible for the on/off.  Having a board which has PFL (or "cue") per channel will make it easier to set the proper input levels.

Happy studying.   
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duane massey

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Re: Where to patch feedback eliminator?
« Reply #13 on: December 15, 2011, 11:32:08 pm »

I have found fbq's to be quite useful is certain situations IF installed and setup properly. A large portion of my clients are non-sound people with no hope of training beyond "ON/OFF", and I still get phone calls about that. My absolutes in dealing with FBQ's are simple. Don NOT use the "live" functions. Run the unit, let it do it's job, and lock it down. Using a graphic EQ to eliminate feedback certainly does more harm to the overall sound than either a parametric or an FBQ, so I don't see the advantage of going to a graphic IF it is for the purpose of eliminating feedback.
If the system is always the same (same mics, same room, etc), then "set and lock" should be very practical.
I don't think FBQ's are a great idea if you have a decent sound person, but they can be useful. I must admit my first response was "don't you mean 'pitch' rather than 'patch', but I don't want anyone to think I am sarcastic....
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Duane Massey
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Re: Where to patch feedback eliminator?
« Reply #14 on: December 16, 2011, 09:43:08 am »

I have found fbq's to be quite useful is certain situations IF installed and setup properly. A large portion of my clients are non-sound people with no hope of training beyond "ON/OFF", and I still get phone calls about that. My absolutes in dealing with FBQ's are simple. Don NOT use the "live" functions. Run the unit, let it do it's job, and lock it down. Using a graphic EQ to eliminate feedback certainly does more harm to the overall sound than either a parametric or an FBQ, so I don't see the advantage of going to a graphic IF it is for the purpose of eliminating feedback.
If the system is always the same (same mics, same room, etc), then "set and lock" should be very practical.
I don't think FBQ's are a great idea if you have a decent sound person, but they can be useful. I must admit my first response was "don't you mean 'pitch' rather than 'patch', but I don't want anyone to think I am sarcastic....

Duane....

I agree that FBX units have some application if, as you say, they are used properly.  I do as you do, letting them set the filters automatically, then locking them down.  As such, the unit has become a parametric equalizer, albeit an "automatic" PEQ.  Even the humble Behringer FBX 1100 can be implemented in such a fashion with satisfactory results.
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John Roberts {JR}

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Re: Where to patch feedback eliminator?
« Reply #15 on: December 16, 2011, 10:58:14 am »

So... how does a feedback destroyer know the difference between feedback (a "continuous, single frequency event" that may be produced by interaction between loudspeakers and microphones) and an extended musical note (a "continuous, single frequency event" that may be produced by some instruments)?
While different devices use different approaches (I ASSume), acoustic feedback has some specific unique characteristics that normal musical notes do not. For example, feedback is generally a simple single frequency, while most musical tones are complex with harmonic overtones. (AFAIK only a flute played pianissimo approaches a pure tone, and perhaps some old synths).

Another characteristic of feedback that differentiates it from music is it's envelope signature. Feed back will generally express as a slowly increasing amplitude, while most musical notes will generally start as loud as it ever gets and decay from there.

Another test to prove if a sound is feedback or music is to hit it with a few dB of cut EQ and see how it acts. Simple music with a 3dB cut will track it's original envelope trajectory, but dropped the nominal 3dB. A building feedback with stop dead in it's tracks or build much more slowly when cut a few dB.

All of these methods to definitively discriminate between feedback and music take time to perform that analysis especially for envelope signatures. So best results should come from time spent letting the device learn the room or system, by cranking up the gain and letting it find the first few worst case modes.

Expecting these to work effectively on the fly will always involve tradeoffs since you can be quick or accurate in your detection, typically not both. 
 
JR

PS: FWIW My FLS blinky lights over the GEQ sliders was not a smart system. it just compared the level in all the different filter bandpasses and indicated which one was loudest. The Peavey MENTOR (now long obsolete) was DSP based and smarter, while it only provided a light show with no actual correction applied. it probably could have in connection with PV's old digital controlled GEQ, but that would have been a pretty expensive solution and real men didn't use feedback killers back then, and PV customers surely didn't pay for expensive solutions, when a cheap one worked adequately.
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Re: Where to patch feedback eliminator?
« Reply #15 on: December 16, 2011, 10:58:14 am »


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