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Wireless Lav Fading and White Noise

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Steve Crow
Wireless Lav Fading and White Noise
on Sep 2, 2011 at 2:28:16 pm

I was on a shoot yesterday and I had the talent hooked up to a Senheisser G2 wireless lav, I was positioned less than 10 feet away however I began to hear the audio fading in and out and also in some instances there was a static-y white noise sound in the background.

The batteries were all brand new and I was getting a strong signal.

Any ideas what could cause this?

I was wondering if perhaps since these Mics are from the pre-digital TV switchover here in the United States that I was no doubt on a frequency that technically was now illegal - could some kind of RF interference cause this "fade out" effect? I filmed just a week ago with these same mics and they were fine - this time I was in a city government building but I've filmed there before without any issues so I am not 100 percent sure this is location related.


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Eric Toline
Re: Wireless Lav Fading and White Noise
on Sep 2, 2011 at 4:05:12 pm

What block or frequency are your G2's? Any frequency above 700mHz is illegal but that doesn't mean it won't work. You could have just experienced an anomolie but the G2's have been known to not work at short distances for some unknown reason.

Eric


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Steve Crow
Re: Wireless Lav Fading and White Noise
on Sep 2, 2011 at 4:49:12 pm

529 and 745 MHZ...still illegal?


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Eric Toline
Re: Wireless Lav Fading and White Noise
on Sep 2, 2011 at 6:01:26 pm

529 is not 745 is. It's not like the FCC is going to come looking for you because you're on 745 but there are other legal users on there that are more powerful that could cause you issues. Actually that could happen on any frequency. Use them both and don't sweat it.


Eric


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Steve Crow
Re: Wireless Lav Fading and White Noise
on Sep 2, 2011 at 6:08:32 pm

Thanks Eric, what concerns me most is finding the cause for this fading and white noise issue...I am going to do some tests this weekend at a different location just to make sure it's not the gear...meanwhile I'm stumped.


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Ty Ford
Re: Wireless Lav Fading and White Noise
on Sep 3, 2011 at 7:03:39 pm

Hello Steve and welcome to the Cow Audio Forum,

In addition to what Eric has mentioned, if one or more of the folks you miced is wearing a blackberry or other wireless device, it can kill your range literally to nothing.

Regards,

Ty Ford

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


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Steve Crow
Re: Wireless Lav Fading and White Noise
on Sep 3, 2011 at 10:06:09 pm

Hmmm thanks Ty that's very interesting....is that because the phone's data or call frequency is close to the lav transmitter's outgoing frequency? Come to think of it, there may also have been a wireless router in the room too.


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Brian Reynolds
Re: Wireless Lav Fading and White Noise
on Sep 4, 2011 at 9:11:16 am

I've had this happen on a couple of occasions in a city area, I now do a scan EACH and EVERY location that I do.
It could be Telecommunications, WiFi, or some sort of data.. But a scan should solve the problem.

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: Wireless Lav Fading and White Noise
on Sep 4, 2011 at 3:33:32 pm

Steve,

I have not experienced any problems I can pin point to a wireless router, but cell phones and smart phones can be problematic. There are more than primary frequencies that can be interfered with. So it doesn't have to be an issue of a device being on the same transmitting frequency.

Regards,

Ty Ford

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


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Jordan Wolf
Re: Wireless Lav Fading and White Noise
on Sep 5, 2011 at 3:30:36 am

You should use the Sennheiser Frequency Finder to see what frequencies are clear in your area. Also, if you call the various tv stations, etc., they should be able to give you the frequencies they broadcast on.

From the description, I don't think that it was a cell phone or PDA, but I guess that's another possibility to consider.

Make sure when you position the bodypack on the talent, the antenna is free-hanging.

Here is a great resource if you haven't seen it yet (I think it would make a good Sticky). There are, thus far, three parts to it, with more on the way, I assume. It applies more for sound reinforcement, but the concepts are relevant for wireless systems anywhere.

Wolf
<><


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Steve Crow
Re: Wireless Lav Fading and White Noise
on Sep 5, 2011 at 8:17:38 am

Thanks everyone, this has been very helpful! :-)
Steve


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Steve Crow
Re: Wireless Lav Fading and White Noise
on Sep 5, 2011 at 8:20:17 am

Oh I did some tests at home and it does definitely look like there was something about that environment I was filming it that caused the mic fading in and out and the noisy signal....next time I will try scanning for a clear frequency, funny that didn't occur to me in the heat of production.


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Jordan Wolf
Re: Wireless Lav Fading and White Noise
on Sep 5, 2011 at 11:55:30 pm

Steve,

Make it a habit to scan for open frequencies EVERY TIME. That's the only way you are (almost) guaranteed a stable signal. You'll want to have every transmitter on set powered on when you do it...you never know when you'll get asked for another wireless mic, etc.

Also, if your unit uses some form of deversity antenna pickup, keep the antennas somewhat perpendicular to each other to increase the likelihood or the unit picking up direct RF from the transmitter and little/no reflected RF.

You'd be surprised how much RF a waterbag, er...person can absorb/reflect. Oh, and be glad that most of you only deal with wireless microphones (albeit a large number sometimes, I'm sure) - when you throw wireless In-Ear Monitors into the mix, the bandwidth gets even more crowded!

Wolf
<><


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