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Background noise removal by phase inversion , how?

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Neil Paisnel
Background noise removal by phase inversion , how?
on Jun 16, 2015 at 4:35:12 am

No idea if this is a recognised technique or how to implement it, but it ocvured to md the other day.

My aviation headset uses a seperate set of mics built into the headset, that pickup external noise, invert it and use it for electronic noise cancellation.


I'd neen recording a stage show where audience noise bleedover to actor mics was a problem.

With a seperste multitrack audio recorder , would it be possible to setup a mic pointing towards the audience, to record audience noise on a single track.
Then later in post, invert that track and apply as and when necessary , say at quiet portions of the stage act or oarticularly loud audience 'response'


?


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Mark Suszko
Re: Background noise removal by phase inversion , how?
on Jun 16, 2015 at 2:01:09 pm

There exist "black boxes" used to cancel echoes and feedback electronically by such methods as you describe, but I'm not certain you can do it as a noise reduction technique in a theatrical space; might be too many variables and the product you get coming out will sound "weird", due to resonances, flanging, and the phase cancellation's effect on the room tone.


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Bill Davis
Re: Background noise removal by phase inversion , how?
on Jun 16, 2015 at 4:20:27 pm

What Mark said. Phase cancellation works best for things like common mode hum where the unwanted signal is sorta simple. The sound of a noisy audience is anything but simple. Plus the frequencies of what you want to keep are typically similar to what you want to remove. Not an ideal situation.

Know someone who teaches video editing in elementary school, high school or college? Tell them to check out http://www.StartEditingNow.com - video editing curriculum complete with licensed practice content.


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Craig Alan
Re: Background noise removal by phase inversion , how?
on Jun 16, 2015 at 9:04:54 pm

what about this vent noise? could I record it and try that technique?

vent noise



Mac Pro, macbook pro, Imacs (i7); Canon 5D Mark III/70D, Panasonic AG-HPX170/AG-HPX250P, Canon HV40, Sony Z7U/VX2000/PD170; FCP 6 certified; FCP X write professionally for a variety of media; teach video production in L.A.


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Mark Suszko
Re: Background noise removal by phase inversion , how?
on Jun 17, 2015 at 12:40:21 am

Yes, with that fan noise, you might try the built-in noise reduction offered by FCPX. Or you can use the free audio app called Audacity to sample a piece of room tone and create the counter-phase to that. You'd export the entire audio track to Audacity in that case, get a noise print, apply it, treat the entire track, then bring it back into your NLE of choice.


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Craig Alan
Re: Background noise removal by phase inversion , how?
on Jun 17, 2015 at 1:00:21 am

Thanks will give it a try.

Mac Pro, macbook pro, Imacs (i7); Canon 5D Mark III/70D, Panasonic AG-HPX170/AG-HPX250P, Canon HV40, Sony Z7U/VX2000/PD170; FCP 6 certified; FCP X write professionally for a variety of media; teach video production in L.A.


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Neil Paisnel
Re: Background noise removal by phase inversion , how?
on Jun 17, 2015 at 5:14:55 am

OK, thanks for the info.
Yes I guess the noise maybe a bit random.

May just be easier to get better mics/mic placement.


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Simon Billington
Re: Background noise removal by phase inversion , how?
on Jun 23, 2015 at 10:25:00 am

You can only try using two mic sources, one to cancel the other, but I believe the others are correct, you will probably cause phasing issues.

You could try the built in a noise removal, but the algorithms are ancient and aren't the best, orpf ten resulting in quite a bit of "musical noise" as side effect.

If that doesn't happen for you try demoing some of the stuff HERE. In fact, as I look, NS1 is on sale. Try not to pay full for any of the stuff here, they have sales all the time.


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