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Chris McElroy
solve audio nightmare
on Sep 13, 2012 at 8:29:13 pm

Yesterday I recorded a speaker in a live event setting and got a horrible noise pattern that I've never heard before. I've attached a short sample and would greatly appreciate comments on what caused this noise. I was using a Lectrosonics 400 series lav with new batteries, going through a Mackie mixer into a Sound Pix 240.
For the first couple of minutes the audio was quite clear - then the devil took hold.

4656_audionightmaresample.mov.zip


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Eric Toline
Re: solve audio nightmare
on Sep 14, 2012 at 1:59:45 am

WOW! That is very strange. Can you recreate the setup at home to see if it's duplicateable? As a guess I would think it's the Pix 240 getting up to speed?

Eric


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David Watson
Re: solve audio nightmare
on Sep 14, 2012 at 6:20:15 am

Did you get this only in the recording? Or did it come through during the event? Could it be the receiver? I've experienced a similar intermittent audio artifact when doing live sound in a church service. The wireless lav/lapel the preacher was using started giving a intermittent hiss sound, similar to what you're getting but more like a hiss. It turned out it was the receiver. You could even see it on the vu meter on the receiver. But this problem was evident during the service; it wasn't something that occurred just in recording.

David H. Watson
dEhiN Entertainment


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David Watson
Re: solve audio nightmare
on Sep 14, 2012 at 6:36:03 am

After I replied I realized that you may also want suggestions on how to remove the audio artifacts. My suggestion would be to apply a noise removal filter: find a point where you hear the artifact alone (when the speaker isn't speaking), use that point of audio as your noise profile. You may have to play with eq afterward, but the frequency of the artifact is pretty distinct and sound fairly low-end. It shouldn't affect the speaker's voice. I'm not sure what software you use to edit, but I've found Audacity's noise removal filter to work quite well. If you want to use Audacity, just use your favorite video editor to strip out the audio to a wav file and work with it in Audacity.

I noticed there was a section where the audio cuts out completely and comes back. I'm not sure what caused that, but there's nothing you can do for that. If it's a problem - having the audio cut out - then try to stylize it by doing a fade out into the cut-out portion, and a fade in afterward. You'll still have your audio missing but listeners will think it's intentional.

HTH

David H. Watson
dEhiN Entertainment


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Chris McElroy
Re: solve audio nightmare
on Sep 14, 2012 at 12:40:52 pm

The audio finally cuts out because I had to pot it down completely. The noise was quite audible over the in-house speakers in the medium sized classroom.
Thanks for your comments.


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David C Jones
Re: solve audio nightmare
on Sep 15, 2012 at 1:36:39 pm

Hi Chris,

Yeah, that had to be annoying! If I had to guess (and that's exactly what I'm doing) I'd say it's being caused by some sort of cell phone interference. At least, I've been in a couple of instances where a similar sound occurred.

Dave J


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Ty Ford
Re: solve audio nightmare
on Sep 17, 2012 at 10:05:48 pm

I'm on the phone with Lectrosonics' Gordon Moore.

As we are talking, he says, and I agree, that this sounds like a bad capacitor somewhere. He has heard it in a microphone but that it could also be in any part of the audio chain; mic, wireless, mixer, camera input, etc.

Gordon said he ran into something like that before, when at a certain temperature, after being on a certain amount of time, the conditions for the capacitor to begin discharging would occur. As the circuit heated up more, the frequency of discharge would increase.

He suggests that you try to duplicate the problem at a different location to confirm that it wasn't some sort of local, external interference, but thinks it was a capacitor. He also asked to add the sound to his very interesting collection of weird audio disruptions.

Whether you find the culprit or not, you may contact him directly, at gordon@lectrosonics.com

Regards,

Ty Ford
Cow Audio Forum Leader


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


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