Noise situation for a documentary

[Bill Wilson]

You will need a mixer for this to work. You need to have one mike wired out of phase acoustically from the mike or 2 mikes you are picking up dialog with.

You point the out of phase mike directly at the offending noise source.
First set the gain of the dialog mikes so you are getting normal recording level on the mixers meter. If you are using a stereo mixer set the pan switches or pots for all of the mikes to either the left or right; they all need to be feeding the same buss.

To make the magic happen adjust the gain on the mike pointed at the noise source until you get maximum cancellation of the of the unwanted noise in the dialog mikes sound. To pull this off the audio operator must use a pair of good headphones that block outside sounds.

What you are doing is cancelling out the noise with the out of phase mike that is pointed at the noise source. The mike pointed at the noise source does not need to be the same type or manufacture as the dialog mike or mikes. They must be wired as balanced low impedance in order to reverse the
the acoustic phasing.

Let me know if you need to know how to know how to check mikes for phasing. it is easy if you have a mixer, either mono or stereo.
Using noise reduction in an editing program will not give the same degree of cancellation.

[Ty Ford]

Originally Posted by Dan Brockett

Hi Dennis:Please tell me that you were a smart boy and recorded with a lav and a boom as everyone should everytime possible?

If you did, you should find that the lav will have a LOT less of the offending noise than the boom. Dan

Hello Dan,

Sorry, but I have to disagree with you on several points.

Split tracking boom and lav doesn't buy you anything unless you aren't sure what you're doing or don't plan to have a qualified sound person listening to audio as its being recorded. If that's the case, split tracking still doesn't guarantee you good audio.

I don't know what your own situations have been, but in the vast majority of cases (not to say there aren't exceptions) for interiors, the right hypercardioid on a boom placed at the edge of the frame beats an omni lav, provided you are able to get within 12-18 inches from the mouth of the person speaking. In this situation, the hyper wins especially as the ambient noise increases. Unless there aren't any mitigating factors, the boom mic wins.

If you can't get that close because of the shot, then lavs MAY win. Again, a LOT depends on the acoustical and noise of the location.

If the rest of the shoot requires the talent to be on a wireless lav, you might as well start that way, just to ensure continuity of sound.

BTW, some folks think a shotgun mic is the only mic to boom with. That's wrong. A good hypercardioid works much better for interiors.

Regards,

Ty Ford

[Dennis Stevens]

Originally Posted by Bill Wilson

You will need a mixer for this to work. You need to have one mike wired out of phase acoustically from the mike or 2 mikes you are picking up dialog with.

You point the out of phase mike directly at the offending noise source.
First set the gain of the dialog mikes so you are getting normal recording level on the mixers meter. If you are using a stereo mixer set the pan switches or pots for all of the mikes to either the left or right; they all need to be feeding the same buss.

To make the magic happen adjust the gain on the mike pointed at the noise source until you get maximum cancellation of the of the unwanted noise in the dialog mikes sound. To pull this off the audio operator must use a pair of good headphones that block outside sounds.

What you are doing is cancelling out the noise with the out of phase mike that is pointed at the noise source. The mike pointed at the noise source does not need to be the same type or manufacture as the dialog mike or mikes. They must be wired as balanced low impedance in order to reverse the
the acoustic phasing.

Let me know if you need to know how to know how to check mikes for phasing. it is easy if you have a mixer, either mono or stereo.
Using noise reduction in an editing program will not give the same degree of cancellation.

Thanks! I would need to know how to check mikes for phasing. I'd also need to get a mixer, since I have one now.

I don't have a mixer either. I've hesitated to get one, since I wasn't sure how beneficial it would be. But it sounds like here it would have been great, if I knew what I was doing!

Some of our interviews are about very sensitive topics, so my fear is to lose something very valuable because the AC was really loud.

[Ty Ford]

For low frequencies, yes. For HVAC hiss, not so much.

Regards,

Ty

[Guy McLoughlin]

Following Bill Wilson's reverse phased mic idea, Hosa makes an inline XLR reverse phase adapter, in case your mixer doesn't offer this.

Hosa Audio Adapter XLR Female to XLR Male Polarity Cross Phase Reverser
http://www.bhphotovideo.com/c/produc...LR_Female.html


- Guy

[Jim Andrada]

Isn't the phase reversal trick basically the same thing the sound cancellation earphones do?

Simply put, is the idea to mic the noise, invert it, and add it into the sound from the other two mic so it effectively cancels out the noise being picked up by the "real" mic(s)

I think all three mics would need to be pretty close to each other so you don't get time lag between the positive and negative noise

Unless I'm missing something (quite possible) couldn't you just record a track with the noise and then invert the signal in your audio software and mix it with the "good" tracks?

Also, wouldn't there be some cancellation of the dialog to the extent that it was picked up on the "noise" mic?

[Guy McLoughlin]

Bill states that the results are better when the NC is done when you are shooting. I haven't tried this, but it sounds like it could work quite well with a directional mic so you avoid killing your dialog.

[Ty Ford]

Originally Posted by Jim Andrada

Isn't the phase reversal trick basically the same thing the sound cancellation earphones do?

Simply put, is the idea to mic the noise, invert it, and add it into the sound from the other two mic so it effectively cancels out the noise being picked up by the "real" mic(s)

I think all three mics would need to be pretty close to each other so you don't get time lag between the positive and negative noise

Unless I'm missing something (quite possible) couldn't you just record a track with the noise and then invert the signal in your audio software and mix it with the "good" tracks?

Also, wouldn't there be some cancellation of the dialog to the extent that it was picked up on the "noise" mic?

Persactly. NCI Miami shows us things that really can't be done.

Regards,

Ty

[Jase Tanner]

How would you compare the capabilities of the 2?

Thanks