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Author Topic: Ringing out a group of mics  (Read 821 times)

Stephen Swaffer

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Ringing out a group of mics
« on: February 03, 2018, 10:35:22 pm »

I think I have pretty much maximized my gain before feedback on our choir mics-but I'm just curious if am overlooking anything.

We are using an A&H QU-32.  I put the choir mics on a group for several reasons-and since I have them on a group thought ringing the group out might give me a little more.  Unfortunately, the first frequency to ring is 400, second is 630.  I cut both a little in the narrowest band I could.  Then to check the impact of the cuts, I copied that PEQ into the flat curve on our playback channel and played music comparable to our choir.  There wasn't much difference.  Doubling my cuts, for learning sake, did make a very noticeable difference in the playback, so I went back to my original settings.

We do have the choir in the monitors a little-but I experimented with monitors on and off and that is really not affecting where it starts ringing.

Given the problem frequencies, I feel like there is little to be gained unless we change the room acoustics?  The choir mic postioning is really what we want as far as coverage and speakers are what they are for right now.
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Steve Swaffer

Kevin Maxwell

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Re: Ringing out a group of mics
« Reply #1 on: February 04, 2018, 12:09:56 am »

I think I have pretty much maximized my gain before feedback on our choir mics-but I'm just curious if am overlooking anything.

We are using an A&H QU-32.  I put the choir mics on a group for several reasons-and since I have them on a group thought ringing the group out might give me a little more.  Unfortunately, the first frequency to ring is 400, second is 630.  I cut both a little in the narrowest band I could.  Then to check the impact of the cuts, I copied that PEQ into the flat curve on our playback channel and played music comparable to our choir.  There wasn't much difference.  Doubling my cuts, for learning sake, did make a very noticeable difference in the playback, so I went back to my original settings.

We do have the choir in the monitors a little-but I experimented with monitors on and off and that is really not affecting where it starts ringing.

Given the problem frequencies, I feel like there is little to be gained unless we change the room acoustics?  The choir mic postioning is really what we want as far as coverage and speakers are what they are for right now.

It depends a lot on the technique that you use to EQ the mics. I put this here as a place holder and sometime tomorrow I will try to post my methods. Can you describe the method you used to "Ring them out".
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Stephen Swaffer

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Re: Ringing out a group of mics
« Reply #2 on: February 04, 2018, 05:06:06 pm »

I just have the system setup like it would be during the choir and bring the group up until the system rings-then try to notch out the offending frequencies.  Use some walk-in playback to "excite" the room as I fine tune.  Our room is very reverberant-usually is behaves a little nicer when full-so I feel like if it doesn't feedback empty, we should be fine with people present.
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Steve Swaffer

Kevin Maxwell

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Re: Ringing out a group of mics
« Reply #3 on: February 04, 2018, 06:00:17 pm »

I just have the system setup like it would be during the choir and bring the group up until the system rings-then try to notch out the offending frequencies.  Use some walk-in playback to "excite" the room as I fine tune.  Our room is very reverberant-usually is behaves a little nicer when full-so I feel like if it doesn't feedback empty, we should be fine with people present.


Here is a cut and paste of my standard reply that I wrote a few years ago.

Here are the basics. This the way I 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 subgroup. 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 subgroup) an EQ and EQ that subgroup 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 subgroup) and I put another mic into another channel thru the vocal subgroup 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 with out 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 separately (or in subgroups).  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 sub group. In other words you would have a wireless lav sub group and a singing sub group, and the other instruments in whatever sub groups you have leftover. It depends on how many sub groups that you have. I then EQ each vocal sub group 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 sub group. In other words you would have a wireless sub group, an apron sub group, an electrics (overheads) sub group etc.. It depends on how many sub groups that you have. I then EQ each sub group 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.
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Jonathan Johnson

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Re: Ringing out a group of mics
« Reply #4 on: February 05, 2018, 04:46:20 pm »

A warning about "ringing out" using the on-board channel EQ (this is for non-parametric EQ typically found on analog consoles):

There is temptation to try to eliminate feedback using the channel EQ. This is not the purpose of channel EQ.

The problem is that the Q-factor (frequency range/bandwidth) affected by channel EQ is far too wide for effective feedback control -- you end up manipulating frequencies that have no business being manipulated, and you affect to the overall sound too much.

Where this turns into a BIG problem is when someone tries to eliminate feedback and ends up turning every EQ knob down... this has two negative effects.

The first effect is that you end up doing little more than turning down the effective gain, because you've actually reduced the gain of EVERY frequency across the spectrum.

The second effect is that this can actually INCREASE the risk of feedback. That's because the EQ doesn't necessarily reduce the frequencies evenly, so between the centers of each EQ band, you can end up with frequency spikes that you now have no control over. When you increase the gain to compensate for the reduced overall signal, you end up boosting these spikes -- and you'll get feedback there which you have no control over.

The purpose of channel EQ is something different entirely: it is to shape the overall sound of the mix, so that different instruments and voices don't overwhelm each other. It lets you bring out the "highlights" of each sound in the mix so, for example, the bass of the keyboard doesn't muddy up the bass of the bass. It also lets you tweak sounds or voices for clarity, for example, to make someone talking more intelligible (as in enunciation, not as in intelligence).

Ringing out is best done with parametric EQ (or notch filter) that allows for very narrow Q (bandwidth).

Channel EQ should only be used for feedback control in a pinch to compensate for poor planning.

Anyway, that's my opinion. I'm sure others have differing understandings and opinions.
« Last Edit: February 05, 2018, 04:51:15 pm by Jonathan Johnson »
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Stop confusing the issue with facts and logic!
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