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Using phase cancelation to eliminate background noise

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Ron Tonkin
Using phase cancelation to eliminate background noise
on Mar 3, 2010 at 11:22:57 pm

Is it practical to set up mics when doing on-camera interviews to intentionally use phase cancellation to remove unwanted background noise, either in realtime, or to manipulate in post?



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Bill Davis
Re: Using phase cancelation to eliminate background noise
on Mar 4, 2010 at 2:31:00 am

It could be.

But most of us prefer to simply mic things correctly in the first place.

The BEST place to suppress background noise is AT THE TIME OF RECORDING.

Using the proper mic. PLACING it properly. And setting levels correctly will get you a clean audio track WAY more often than trying fancy electronic tricks in post.

Said shorter - fixing something is always harder than having nothing to fix.





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Brian Reynolds
Re: Using phase cancelation to eliminate background noise
on Mar 4, 2010 at 6:51:23 am

I have used phase cancelation on a few occasions, the most stunning result was for live crosses to a TV "Eye in the Sky" helicopter, the microwave link had a video and 2 audio channels. I used one of the audio channels for the jurno mic the other as an FX channel where an omni mic was used. Both channels arrive at the on air audio console, ch2 was phase inverted and mixed into the program providing a significant reduction in the annoying helicopter FX.
A lot of phase reverse tricks do work well.... but its ALWAYS better to get good sound first than trying to fix problems in post production



The difference between Knowledge and Wisdom is... Knowledge is the knowing of facts.... Wisdom is the sensible application of good quality knowledge...


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Ty Ford
Re: Using phase cancelation to eliminate background noise
on Mar 4, 2010 at 1:06:15 pm

Hello Ron,

Brian and BIll are spot on. Another answer is, "it depends..and you'll never know until you try, but doing so during production can reduce the quality of your audio.

Theoretically, yes, adding two identical signals combined with one signal reversed in polarity (slightly different than phase) can result in cancellation. Will it cancel the noise you want without canceling the audio you want? Dunno.

Cancellation works best if the noise is constant in volume and spectra and place of origin. Any variation reduces the effects of cancellation. Practically, lower frequencies are more easily cancelled by using two identical mics, with one of reversed polarity. It also usually helps if the mics are close to each other so they are truly hearing the same thing.

Regards,

Ty Ford

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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Ron Tonkin
Re: Using phase cancelation to eliminate background noise
on Mar 4, 2010 at 4:54:46 pm

Getting it right the first time is the goal. Always looking for more tools for my belt! Thanks for your input - I'll be spending more time on your forums.



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