Tips and Tricks To Track Down Feedback

  1. #1 by Mike Carlson on 07-11-2018
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    Tips and Tricks To Track Down Feedback

    Looking for some tips and tricks on what tools are available in the X32 to track down feedback when it happens. I try to watch the RTA or use the EQ to pull back the frequencies that I think are causing it. Sometimes it takes me a bit to hunt it down.

    Im fairly new to the X32 and I was wondering if anyone has any tips for that they may use on the X32 to quickly track down what the feedback source is.

    I also realize its a pretty broad and general question. =)
  2. #2 by Robert Lofgren on 07-12-2018
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    There is no ĒproperĒ way to find what is causing feedback other than pulling faders.

    However, proper feedback hunting before the show starts is essential so that you may ring out your system not to be on the verge of feedback.

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  3. #3 by Mike Carlson on 07-12-2018
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    I totally understand there is no "proper" way to do it, I am just wondering if anyone has any tips and tricks on what they use. RTA in the X32? Some 3rd party app? Apps that teach you frequencies so you can isolate whats feeding back, etc.
  4. #5 by Kevin Maxwell on 07-12-2018
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    Very long reply.

    Below is basically a cut and paste of something I wrote before to answer the same basic question.

    BTW I just watched the first video that Steve linked to and you will see what I wrote below about exciting a sound system. The way he is just sweeping without exciting the sound system at times is prone to issues like I mention below. Also in the X32/M32 there are Parametric EQs on the Mix Bus so why do that method and have to translate it to a graphic EQ, just use the parametric on the bus that you have the graphic on. Also there are stereo and dual versions of the 2 basic types of Graphic EQs in the X32/M32 the basic one and the TruEQ. If you look in the ownerís manual they explain the differences. In the basic one the filters donít really blend together, the TruEQ give a result that is more like you would get using a parametric EQ the filters work together to give a smoother result.

    I also watched the second video and have a few problems with that one also. First the pink noise in the X32/M32 isnít flat and other pink noise generators arenít always flat. So if you EQ to that you will get some strange results. Also when you use a single mic like he is to EQ a system you are only testing for that one place in the room it may sound different in different places in the room. And sometimes what you are seeing in a measurement system is something that you canít EQ. Knowing what you can and what you canít isnít necessarily easy for a novice to know. Boosting an EQ to compensate for a problem in the room will cause other problems.

    So my basic review of these videos is they may help you if you are extremely conservative in what you do to EQ a system. There is a lot you canít fix with EQ.

    Here are the basics. This the way suggest that you try to tune a system.

    This is assuming that everything else in your system is set up properly and we are talking about overall system equalization. My method also assumes that you have a 2nd channel of EQ to insert on a vocal Mix Bus. This doesnít even take into consideration on how to EQ the monitors. That will cost extra.

    The technique that I use for EQing a system is Ė I EQ the system for linearity, in other words what goes in is what comes out. Or as close to that as I can get. I use a software program called SMAART. This can be done by ear also but not as quick and as accurate as when using SMAART. I will assume that you do not have SMAART.

    So to do this by ear - I would usually play a bunch of different tacks from different CDs that I am very familiar with the way they sound. What you are trying to do here is to get the system to accurately reproduce the way the CD sounds. While playing the CD I then would listen for the things that donít sound quite right. I like to only cut frequencies when doing system EQing. To pinpoint the offending tone sometimes it helps to boost the suspected offending frequency when hunting for the right one. So boosting the frequencies to make the bad sound stick out more. Sometimes you find that it isnít the one you thought and you need to try another one. This means bring up the control of that frequency and if its not the right one bring it back down, when you find the frequency you are looking for you would then cut that frequency, how much depends on what it sounds like. I like to be conservative but you can get the feel rather quickly as to how much of a cut to make. When you are all done using this method you should hopefully find that you havenít hacked the EQ to death. Also try hitting the bypass switch to see the difference with the EQ in or out of the system. It may be a very minimal difference.

    I then insert (on the vocal Mix Bus) an EQ and EQ that Mix Bus for gain before feedback. The way I do that by ear is to have a vocal mic on stage that is on thru the system (thru the vocal Mix Bus) and I put another mic into another channel thru the vocal Mix Bus back at the mixer. I then, while using my voice at a decent level, slowly bring up the mic on stage till it starts to slightly ring (while I am making various noises and talking) I then find that frequency and cut it a bit and continue this till I start to get multiple frequencies ringing at the same time. This is usually the point at which you canít get any farther without hacking the EQ to death and screwing up the sound. All this while I am paying attention to how my voice sounds. This is to give your vocal mics the best GBF (Gain Before Feedback) that you can reasonably expect. If you do this without exciting the system with your voice you will be surprised at the frequencies that pop up when a person gets on stage and talks into the mic. I find most micíed instruments donít usually have a problem with gain before feedback and playback (CD) and instruments donít need the additional EQ that the vocals do. When more EQs are available you can breakup what needs to be EQed for GBF and do them in each Mix Bus. If you try to do a best gain before feedback EQ on the whole system you take the life out of playback and a lot of instruments. Now of course this is assuming you have that kind of flexibility to the system.

    (For church)
    If you were doing the church system using lavaliere mics on the preacher/speaker and handheld or in stand mics like the SM58 for the singers, I would route each of these types of mics to its own Mix Bus. In other words you would have a wireless lav Mix Bus and a singing Mix Bus, and if you want to you can put the instruments in whatever Mix Bus you have leftover. It depends on how many Mix Bus that you have. I then EQ each vocal Mix Bus separately. Then the channel EQ on the mixer can be used for tonal shaping for each mic.

    (for theater)
    If you were doing the traditional theater system using mics on the apron of the stage (apron mics) and mics hanging over the stage (over head mic) I would route each of these types of mics to its own Mix Bus. In other words you would have a wireless Mix Bus, an apron Mix Bus, an electrics (overheads) Mix Bus etc.. It depends on how many Mix Bus that you have. I then EQ each Mix Bus separately. Then the channel EQ on the mixer can be used for tonal shaping for each actor.

    I find that when I EQ a system with SMAART I can do it quicker then I can with just my ears and I think I get a more consistent sound. And I even have a technique for EQing the vocal inserted EQs using SMAART.

    In my opinion pink noise with an RTA is useless no matter how flat you might think it is. Years ago before Smaart existed I used to use an RTA and I never used pink noise with it. When I had one to use I used it to confirm or tell me what frequency I was hearing by seeing it react on the RTA. And using the techniques I wrote in my long post.

    With a program like Smaart there is a learning curve so it isnít a quick program to learn. But with Smaart you compare what you are feeding to the system (pink noise is good for that) and what you are getting on your measurement mic or mics. And what you are going for is linearity, what goes in is what comes out. At least that is how I do it. I have been using Smaart since Version 2 and have been paying for upgrades all along. It is now up to version 8.
  5. #6 by Jason Maxfield on 07-15-2018
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    Others have covered this pretty good at this point, but I can tell you how I did it without any other tools or software just using the X32.

    I go into the effects of the console and insert a dual 31 channel EQ on whatever buss I'm using for monitors... in my case I have 2 standard, and have up to 5 at once. I used the same technique for all monitors I setup.

    Once you have a monitor set up with a mic in front of it, I used a Shure SM58, I put the gain fairly hot, around +30. I would take my monitor volume slider and slowly crank it up, while I'm looking at the effects channel of that monitor (that being buss 1 for my left monitor and buss 2 for my right monitor, set up as A, and B).

    Once I start to get some feed back you can see the frequency on the RTA and you simply notch the frequency down until it doesn't feedback. Sometimes you have to adjust adjacent frequencies to nail it down.

    It's a bit harder doing it yourself. It's much easier if you can get someone to stand up on stage and talk into the monitor and do silly things like cup it or put their hand over the mic causing feedback intentionally.

    Be aware that you will lose some gain as you notch various frequencies out, but overall I could push my slider +10db higher once I did this. It's also good for when you get people handling mics improperly when singing. It's very rare if I get any kind of feedback.

    If you end up notching too many frequencies, your monitors could start to sound awful, so be careful. Working to find a better position for the monitor and making sure your polar patterns (I.E. cardioid has best rejection at the rear of the mic) on your mics are working at your best interests is better than notching a bunch of offending frequencies.

    Granted some sound people will tell you that you shouldn't have to use EQ to tame feedback and only use it as a last resort. For me, and the room I deal with it's very acoustically live where the stage is, has a low ceiling, so sound from the monitor can bounce off the ceiling and down back at the mic, specially in the high frequencies from the tweeter, which I tend to roll some of the high-end (8Khz+) off, just to avoid that to begin with on the buss EQ of the monitor before I even insert the 31 band EQ.

    Hope that's helpful.