mic noise

[TechWench]

so during the last show i did the mics were peaking REALLY bad.
so this guy who did sound came and said that you have to like...ride it out of the system.
so before the show he basically pushed them all up one by one trying to get rid of the mic noise..
now im not a sound person.
but when he started doing this i was confused.
so ya, i was just wondering
is this a normal thing?
do real theatres do this on a regular basis?
i was very skeptical and it didnt really work out too well.

 

[avkid]

bringing the levels up one at a time? yes, that is the sound check

 

[ccfan213]

well it doesnt really push it out of the system, one technique of sound checking does involve pushin the system to the point where it feeds back prior to the show so you know how much leeway you have during the show itself and can avoid feedback, this guy probably thought that once he did that he was done and didnt eq properly, the only downside to mic checking like this is that it pisses evereone off.

 

[bdesmond]

Well, it isn't like you can push the fader up to its max and the little men on the line will get blasted out of the speakers and you're set.

Likely what he was doing as someone else said was seeing at what levels the mics would feedback.

Usually you can putz around with the EQ on the mixer and get rid of hums, buzz, other extraneous noise. If you've got a persistent noise issue, you may have an electrical issue - e..g power cable crossed with a mic cable, that sort of thing...

 

[great_beyond]

what he was doing was, what I call ringing out the system.

-Bring each fader up to the point of feeding back so that one you know how much gain before feedback you can achieve. And EQ the mic to gain more Gain.

This is an essiential step in any sound system setup, to make sure you can get as much out of the system as possible.

 

[IcePenguin]

Wait, were they PEAKING (also called CLIPPING, when a sound wave curve gets forced into square-shaped waves due to the amount of amplification) or FEEDING BACK (that squealing noise when a mic's signal is amplified too much and it picks up its own signal)?

If they were feeding back, did the tech just run the fader up 'till it fed back and bring it back down? Did he change any EQ or gain settings at all? I'm confused by your description.

 

[TechWench]

ya it was feeding back...sorry we call it peaking in our theatre.
he wasnt just doing a mic check, he was like you guys said pushing the slider all the way up to make it feed back.
and he kept saying that by doing so now, it wouldnt happen during the show.
which i thought was wrong.
cause like bdesmond said its not like the little men are gonna get blasted out of the speakers.
but thats what it sounded like he thought was going to happen
good...im not a fool, he is!
thanks!

 

[ccfan213]

well in a sense, if he does the right thing you are both right, the feedback elves as they will from now on be called will remain in the system, but he has created a situation where he is in control and knows how far he can go before he gets feedback and there fore can prevent it from occurring.

 

[TechWench]

hmmm...ya about that...
he was the SM for this show...
he wasnt even in the same room with the sound board...
and the sound op...was nowhere to be found while he cleared the system.
:?
thanks guys!

 

[mbenonis]

ya it was feeding back...sorry we call it peaking in our theatre.
he wasnt just doing a mic check, he was like you guys said pushing the slider all the way up to make it feed back.
and he kept saying that by doing so now, it wouldnt happen during the show.
which i thought was wrong.
cause like bdesmond said its not like the little men are gonna get blasted out of the speakers.
but thats what it sounded like he thought was going to happen
good...im not a fool, he is!
thanks!

Actually, what he was doing was important, and neither of you are fools - you need to be able to set the fader to +10 dB during a show without the risk of feedback. I do this myself before a show - especially a musical, because our system is very prone to feedback with our lapel mics. And during a musical, the live band is often 20 strong and is quite loud, even when playing as piano as possible.

Here's what you do, just to clarify: Have the actor stand center stage with their mic on, and have them start saying their lines. Bring the fader all the way up to +10, then adjust the gain until the system feeds back. Then bring it down slightly, and have the actor walk around the stage. If he/she doesn't feed back, you're set. If he/she does, dip the gain slightly and repeat.

Btw, you need to start referring to feedback as feedback, not peaking. As IcePenguin stated, they are very different things and it's important to use the correct term when describing something to a professional (or another sound technician/designer).

 

[The_Guest]

...Bring the fader all the way up to +10, then adjust the gain until the system feeds back. Then bring it down slightly, and have the actor walk around the stage. If he/she doesn't feed back, you're set. If he/she does, dip the gain slightly and repeat...

Actually you should properly set the gain first, via PFL'ing the channel onto the consoles meter. Then establish where the feedback point is on the fader, which should be somewhere far beyond unity. If done properly, you'll have a much better gain structure. Plus, you'll experience lower noise and more headroom. You should never set your gain until the mic feedbacks and drop it down, you're asking for trouble. For more about properly setting gain levels, consult you're consoles manual.

Since most of us here are using Mackie mixers or similar consoles, here's what their VLZ-PRO's manual states...

http://www.mackie.com/pdf/1604vlzpro_om.pdf (Go to "Level-Setting Procedure)

 

[mbenonis]

You're right, Jeff - that is a good thing to do before starting to find the feedback levels.

 

[TBNAudioEngineer]

If using WHICH MACKIE??

There are a few different models of mackies, some aren't selectable PFL in solo mode. The VLZs (24.4 and 32.4) use PFL. the 8bus (16.8,24.8, and 32.8 ) series use AFL for the solo, and is not switchable.
EQing "hot frequences" can remove feedback, but you have to be careful not to "color" the signal to where it's unnatural sounding. The point should be to eq as close to what a person talking or singing (signal) would sound like without a mic. This isn't always possible depending on room acoustics, monitor systems....etc. But be carefull you don't OVER-EQ. Voices that sound very "thin" are a result of too much high frequency boost, or not enough low-midlow frequencys. Learning the right way to EQ is process of trial, error, refinement. Just keep trying until you get it right.

Jonathan G. Phillips
WDLI - Canton, Ohio
TV Audio Engineer