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Odd Lav Issue

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Smith Glover
Odd Lav Issue
on Dec 10, 2009 at 9:51:49 am


This is an odd audio issue- hopefully I can explain it clearly. The basic issue is that I am having trouble with my wireless lav system- it is an Audio-Tehcnica 88W- not the greatest system but it has served me well.

After a couple of years of solid use, I noticed that I was intermittently getting static in that mic. The static would get lesser and greater at seemingly random times. I used it on a different camera and the same thing happened (switched from my DVX 100 to PD150).

Then I noticed it was happening badly one shoot- however, it didn't seem to be the lav's fault. I simply put my XLR to mini into the XLR socket, and immediately that channel would start to spike with static, without me even putting the min jack into the lav system. In other words, just putting the XLR cable in caused an issue. I then put the cable in another camera, thinking mine was broken, and same problem. I tried a brand new XLR chord, and SAME PROBLEM. Very weird. On the shoot, I fiddled with the chord until by some miracle, the static died down and everything was fine. I have no idea what changed.

Anyway- I went through this same problem again a few days later, except this time the phantom static wouldn't go away- changed cameras, attached the lav system to the XLR cable and then just had the XLR cable attached- not matter what, there was a static spike in whatever channel I put the XLR cable into. Then today I tried and everything is fine.

I know this sounds weird, but I have no idea why I am getting phantom static sometimes with just an XLR chord (and also with the wireles lav attached) and sometimes not. In between I also rented a better wireless system (Sennheiser) and something else happened- everything seemed fine while recording, but when I listened to the tape, the wireless audio track would spike with a totally different type of static, much more intense. While it did this, the audio from the shotgun in the other track would be pulled down to barely audible- no static, just lowered volume. Again- no idea why this would be.

I am beginning to think I have a static charge that is causing the issue. Regardless- if you have read through this I thank you and would love to hear your thoughts.


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Ty Ford
Re: Odd Lav Issue
on Dec 10, 2009 at 12:08:18 pm

Hello Smith and welcome to the Cow Audio Forum.

Let's see. You're plugging a wireless receiver into a DVX 100 or PD 150 XLR input. The phantom power on the camera should be turned OFF. You only use Phantom Power with hardwired mics that require phantom power. Doing otherwise can cause problems.

"putting a jack into a lav system" Do you mean connecting the wireless receiver to the camera? There are jacks and there are plugs. You insert plugs into jacks. Is that what you're talking about?

It's not unusual to hear noise if you listen to a mic input with no mic plugged in. That's called an unterminated connection.

It may also be possible that your problem is in the mono to XLR cable.

Phantom Power doesn't cause static.

Having noise on one track pull down the level of another is usually caused by an Automatic Gain Control (AGC) feature turned on. Check your camera menus.

What happens if you plug one or two XLR mics into the XLR inputs of these cameras? Not all mics require Phantom Power. Engage Phantom as necessary. If the noise goes away, you know the fault lies in your wireless connections.


Ty Ford

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

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Sam Mallery
Re: Odd Lav Issue
on Dec 10, 2009 at 11:06:34 pm

I don't know if this will solve your problem, but when you use the 88W system with an XLR output, you should use the CP8306 output cable:

It has a transformer that corrects the signal flow. Also, try changing channels. The 88w has two channels. One may be getting interference. Also, instead of renting a Sennheiser, hire a local location audio person. Your chances of getting unexplained hell static go down considerably when you do this.

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Bill Davis
Re: Odd Lav Issue
on Dec 11, 2009 at 12:39:25 am

Oh for gods sake, Sam.

You know that in the modern era the way to solve all problems is to buy cooler equipment. (full sarcasm mode on)

You keep talking like this and you'll start people thinking that the equipment is subservient to the brains of the people using it - and that decent equipment in the hands of experienced users produces better results than "cool" equipment in the hands of the clueless.

And if that kind of radical talk persists, our "short attention span" economy will surely suffer!

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Smith Glover
Re: Odd Lav Issue
on Dec 11, 2009 at 7:26:24 am


Thanks for your thoughts. When I said "putting a jack into a lav system" I did mean plugging the mini part of the XLR cable into the wireless (jack into plug).

The phantom power was on, which might have been the issue- I am giving it a test run tomorrow. I am not sure if the AGC was turned off at the time as I showed the camera to someone today and they messed with a few settings- regardless, it's off now. The maddening part is the inconsistency- I am pretty careful when it comes to checking what steps I take to solve a problem- and the phantom static I get truly seems to be random.

Regardless, thank you for answering my question- I'll check it out tomorrow and report back if the issues arises again.



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Joel Servetz
Re: Odd Lav Issue
on Dec 11, 2009 at 1:18:30 am

Are you sure what you're describing as "static" isn't just interference from a strong transmitter near your operating channel? VHF wireless mic. systems, especially older, less expensive systems like the Pro 88W can be very susceptible to interference in very rf rich environments. Where are you located? I know that older vhf mics. I've used in the NY/NJ metropolitan area were sometimes subject to occassional spikes from public safety, expecially FDNY which still uses vhf radios. A hospital I did some work for in suburban NJ was getting occasional spikes from their own security radios, which was ok by me because then I got to rent them my mics instead. If your receiver has a peaking indicator, see if it's lighting up or flickering without your transmitter being turned on. But really, a better long term solution, if you've got the dough, is a really good, moderately priced frequency agile, true diversity system like the Audio Technica 1800 series.

Joel Servetz
RGB Media Services, LLC
Sarasota, Fl

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Jordan Wolf
Re: Odd Lav Issue
on Dec 14, 2009 at 9:19:40 pm

Okay, so let's condense this down a little bit:

Symptom: Static coming from a wireless microphone system.

Variables Eliminated:
1. Input cable (from mic element to "mini" connector)
2. Output Cable (from receiver to camera input)
3. Camera

Variables NOT Eliminated:
1. Wireless Transmitter (input jack, wireless frequency selected, squelch control)
2. Wireless Receiver (output jack, frequency selected, squelch control)

Actual Problem:
1. RF Interference
2. Bad Connection (intermittent, oxidized, etc.)

How to diagnose the actual problem:
1. RF Interference - verify that your wireless system is not using the same frequency range as that of local TV stations and other broadcasts.

2. Bad Connection - For "intermittent", which can happen from repetitive insertion/removal of plugs into jacks, you can wiggle the connector while it is seated in the jack to try and recreate the static. The jack might be mounted to the PCB inside the wireless unit and might have come loose. For "oxidation", usually caused by exposure to moisture, salt water, etc., you might try some Caig DeOxit.

How to fix: If not user-serviceable (change of frequency, squelch setting, etc.), return to factory for repair.

That's my take on it.


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