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Background noise removal by phase inversion , how?
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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7 Replies
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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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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.
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what about this vent noise? could I record it and try that technique?
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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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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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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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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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.
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