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Wireless lav mics- how to avoid "audio spillage"?

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Max Palmer
Wireless lav mics- how to avoid "audio spillage"?
on Dec 12, 2012 at 2:39:51 pm

Some of you may have seen my previous post last week about buying wireless lav mics. I happened to seek out another department in my company who just so happened to have two brand new Sennheiser G3's wireless lavs for me. Bingo!

I used these yesterday for the first time in a mock newscast for my department, with two presenters sitting next to eachother. I'm extremely pleased with the outcome and quality of the mics. My only problem, is that the audio from one presenter would spill into the other presenter's mic, and cause a sort of "audio ghost" in the opposing channel. Not a HUGE problem, seeing as I can just zero the audio in the opposing channel when one person is speaking. But in the future, is there a better way to prevent this from happening? Were my mics too sensitive? I had them dialed in on the camera so they weren't clipping, but perhaps I had them too high.


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Ty Ford
Re: Wireless lav mics- how to avoid "audio spillage"?
on Dec 12, 2012 at 2:54:07 pm

Hello Max,

What you're experiencing is normal. You can reduce some of this in production with an automixer that automatically turns down mics that aren't being spoken into. Audio Technica and Shure both make models.

If not that, then you do it in post by reducing the gain on the mic not being spoken into using the editing software. You have to do this each time the talk goes from one person to another. It's takes a little time but after you get used to the hand motions, you can fly right through a production.

If your software has gates for each track, they might be able to do the job, depending on how loud the offending voice is.

Regards,

Ty Ford
Cow Audio Forum Leader


Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
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Eric Toline
Re: Wireless lav mics- how to avoid "audio spillage"?
on Dec 12, 2012 at 2:58:13 pm

What you experienced is a common problem when talent is close to each other. Moving them a bit further apart might help but will not eliminate the problem.

Closing mic A when B is speaking & vise-versa is fraught with peril as you might miss an unexpected response from the closed mic. Seperate tracks for each talent would be a must then you can play with it in post. Watch a local newscast and see if you hear the same issue there.

Eric

"I push the RECORD button and hope for the best"


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Bill Davis
Re: Wireless lav mics- how to avoid "audio spillage"?
on Dec 13, 2012 at 4:30:21 am

Max.

Since you're learning about microphone use here's a tip.

Remember the inverse square principal.

Look at where you are placing your microphones. If you have them mounted as "tie tack" locations - say one foot down from the mouths of each of two talent who are positioned close so the mics are, say, just 3 feet apart - that arragement gives you vaguely around a 9 to 1 difference in the pickup level of the speakers voice hitting THEIR lav compared to their voice hitting the lav mounted on the non speaker. (The square of 3)

If you simply halve the distance on each mic position - to 6 inches from the talent's mouths - then you're doubling the proximity ratio from 1 to 3 - to 1 to 6 - and giving you a 36 to 1 difference.

This is simplified, but it kinda shows you a bit about why small moves in mic position can have a much larger effect on stuff like feedback and microphone bleed then you might initially think.

Relatively small position changes can be a big deal.

A general good practice is to try to keep two open mics separated by at LEAST 3 times the distance to the source they're recording and why a bit more is always a LOT better.

You'll get a fun demonstration of the practicalities of this the first time you use two lavs to mic a couple in a scene that have to kiss.

When the two mics get close to having their positions "evened up" - all hell typically breaks loose regarding phase cancellation and audio crap.

Just some thoughts to help you as you're learning wireless.

Yours in fun with audio...

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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Peter Groom
Re: Wireless lav mics- how to avoid "audio spillage"?
on Dec 13, 2012 at 3:28:49 pm

Youll always get this sort of spill with 2 mics close together.
You should be able to lessen the audible off mi sound in the mix
Peter

Post Production Dubbing Mixer


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Chris Wright
Re: Wireless lav mics- how to avoid "audio spillage"?
on Dec 15, 2012 at 1:52:21 am

What if you slightly modify the pitch range for one of the tracks, One of the voices would be a slightly higher or lower pitch,then phase cancellation can't appear.


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