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Author Topic: Mic sensitivity vs gain  (Read 12227 times)

Aaron Kennedy

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Mic sensitivity vs gain
« on: January 17, 2018, 08:43:38 pm »

Can someone help me understand the difference between Mic Sensitivity and audio board gain. Is there any advantage between turning one down and the other up? I constantly battle feedback when running the board for our schools musical. We typically run 15 wireless sennheiser mics along with a few wired mics. We have two different sets of monitors and then the house. We also have about 15 pit instruments (not micd). When I first try setting everything up, I tone out all the mics, but after a few rehearsals I am battling everything again. I'm assuming that I just have things too sensitive. The biggest issue is ensuring the actors can be heard over the pit. Any advice is appreciated.

Thanks
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Ivan Beaver

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Re: Mic sensitivity vs gain
« Reply #1 on: January 17, 2018, 09:02:33 pm »

Can someone help me understand the difference between Mic Sensitivity and audio board gain. Is there any advantage between turning one down and the other up? I constantly battle feedback when running the board for our schools musical. We typically run 15 wireless sennheiser mics along with a few wired mics. We have two different sets of monitors and then the house. We also have about 15 pit instruments (not micd). When I first try setting everything up, I tone out all the mics, but after a few rehearsals I am battling everything again. I'm assuming that I just have things too sensitive. The biggest issue is ensuring the actors can be heard over the pit. Any advice is appreciated.

Thanks
You can play all the "gain games" you want, but the real end result will not change.

Gain before feedback is based on many factors, NONE of which are mic gain, or any gain settings on the console.

Let's say your system has a maximum gain of 100dB before feedback. Let's say there are 4 gain stages.  It does not matter if 1 stage has 97dB and others each have 1 dB or each one has 25dB, the end result is 100dB.

If you work through various PAG-NAG equations, you will realize that the thing that makes the biggest difference in gain before feedback is getting the mic closer to the source.

There are other factors, location of speakers, pattern of speakers, response of the system, eq of the mic and so forth.
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Mac Kerr

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Re: Mic sensitivity vs gain
« Reply #2 on: January 17, 2018, 09:15:08 pm »

Can someone help me understand the difference between Mic Sensitivity and audio board gain. Is there any advantage between turning one down and the other up? I constantly battle feedback when running the board for our schools musical. We typically run 15 wireless sennheiser mics along with a few wired mics. We have two different sets of monitors and then the house. We also have about 15 pit instruments (not micd). When I first try setting everything up, I tone out all the mics, but after a few rehearsals I am battling everything again. I'm assuming that I just have things too sensitive. The biggest issue is ensuring the actors can be heard over the pit. Any advice is appreciated.

Thanks

What are you talking about? Mic sensitivity refers to an intrinsic characteristic of a given microphone, how much voltage it puts out for a certain level of input. It is not something you can change. Input gain is the first stage of gain that raises the very small voltage that the mic puts out to a high enough level to overcome either the internal noise of the mixer electronics, or the digital resolution. To get a better signal to noise ration you run the mics with more input gain, to prevent overload you run them with less.

The other gain points you pass through would be the output levels of the mixer, and for balancing the levels of the performers and/or instruments, the input faders.

The biggest cause of feedback that you are probably running into is using stage monitors with lav type mics. It takes a pretty skilled operator to mix a musical with monitors, and it takes a lot of turning down mics that aren't active. In a Broadway musical the mics get mixed on a line by line basis. And there are minimal monitors that have the lav mics in them. Monitors are about letting the cast hear the important parts of the band, piano for pitch, snare and hat for timing, etc.

Ivan explained about how where in the signal chain the gain comes does not impact feedback, it is the total gain through the system, microphone to speaker.

Mac
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Corey Scogin

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Re: Mic sensitivity vs gain
« Reply #3 on: January 17, 2018, 11:47:06 pm »

What are you talking about? Mic sensitivity refers to an intrinsic characteristic of a given microphone, how much voltage it puts out for a certain level of input. It is not something you can change.

He's referring to what most wireless mic manufacturers (if not all) call the input gain setting on the microphone transmitter. In Aaron's defense, they do call it "sensitivity".
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Len Zenith Jr

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Re: Mic sensitivity vs gain
« Reply #4 on: January 18, 2018, 12:03:37 am »

Is there any advantage between turning one down and the other up?

There is but it isn't gain before feedback. Having a weak signal that needs a lot of gain at the end of the signal chain increases noise in the system as the huge increase in gain at the end also increases the noise floor from all the components in the chain the same amount. A strong signal to begin with reduces that.
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Debbie Dunkley

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Re: Mic sensitivity vs gain
« Reply #5 on: January 18, 2018, 12:40:25 am »

Speaking of such things.....
The singer in one of  Chris's bands uses a wireless Senny EW100. There is a local venue that they play with an in house PA which is one of the few places the band doesn't use me for sound. Each time they play there I have to turn her mic receiver sensitivity up at least 12db from what we normally use to get that board to even recognize the signal. The gain has to be way high on the channel input too.
I use a A & H QU-PAC and the venue uses a A & H GL ( 2400 I believe). That seems quite a difference.
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Len Zenith Jr

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Re: Mic sensitivity vs gain
« Reply #6 on: January 18, 2018, 01:02:14 am »

^^ Sounds like a mic/line level issue. Look for a switch/push button on the board.
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Scott Holtzman

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Re: Mic sensitivity vs gain
« Reply #7 on: January 18, 2018, 01:45:47 am »

^^ Sounds like a mic/line level issue. Look for a switch/push button on the board.

There is a line pad on the Gl2400 just above the input gain.

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Chris Grimshaw

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Re: Mic sensitivity vs gain
« Reply #8 on: January 18, 2018, 05:52:31 am »

If they're going in on 1/4" jacks, the desk might be expecting line-level and will need plenty of boost to get it back up again if the receiver is putting out mic-level signals.


To the original poster, chances are things like mic positioning is changing, possibly without you knowing. Maybe you've got directional mics and someone's clipped them on upside-down or something silly like that.
However, stage monitors in a situation like this is just asking for trouble, IMO, unless you're extremely careful with what you send to them, and keep the volume low.

Chris
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Debbie Dunkley

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Re: Mic sensitivity vs gain
« Reply #9 on: January 18, 2018, 09:38:39 am »

Unsure which position that channel pad switch is on the mixer - I assumed it was correctly set because all the other vocal mics and drum mics are fine. The guys who run the sound do it all the time and I didn't even consider the pad switch because it such basic thing.
I don't get to see the mixer - and I don't really involve myself too much in the sound. It's one of the rare occasions I get to  go as an audience member and I have a few drinks.
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Re: Mic sensitivity vs gain
« Reply #9 on: January 18, 2018, 09:38:39 am »


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