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Old August 11th, 2008, 08:12 AM   #1
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Random Audio glitch

I recently filmed a 2 day conference with my trusty Sony PD 150 camcorder. For the conference speakers I had my Sony ECM-NV1 microphone(the one that comes standard on the camera) on a stand about 2 to 3 feet from the speakers mouth. It was connected to the PD150 by a new 80 foot Low Noise XLR microphone cable. Attached to the camera on channel 2 was a Sennhieser 66 shotgun microphone for room audio and as a backup.
Unfortunately I ended up with a random sound glitch on channel 1 from the speakers microphone. Over the 8 eight hours of recording I ended up with maybe 20 of these. Most were single glitches but there were several that occurred within seconds of each other.

On this page: http://tinyurl.com/676e7u I have included a short video segment that shows the problem with a double glitch a few seconds apart. Underneath is a close up of what one of these double glitches looked like on my Vegas timeline. . . . .Sony mic on top, Sennhieser underneath.The video also shows some video noise that occurs at the same time as the audio glitch. . . . but that happened only on this clip. Video was recorder ed directly to a notebook computer via firewire and tape was running in camera as a backup. Audio problem is on both direct to hard drive recording and mini DV tape.

I had both channels setup on manual control and I kept audio at a max of -12 to -20. My initial thought was that when I was adjusting these levels during the day the glitches may have occurred. I have since done some testing and have been unable to reproduce this problem by doing what I did that day.

There were a couple of notebook computers running within a couple of feet of my front microphone and a remote control to change the PowerPoint presentations but I wouldn't imagine that would produce this problem. . . . does anyone have any idea's?

Mark
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Old August 11th, 2008, 10:38 AM   #2
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I'm looking at your message right now on a computer that doesn't have speakers so I can't listen to confirm my suspicions but that kind of interference pattern and its appearance sure makes me suspicious of an infection of 'Blackberry'itis.' Them little crackberrys produce a lot of RF noise as messages come in, enough to even intrude into hard-wired systems. Could have been picked up by the mic electronics or directly in the camera even though you had a balanced cable run. I'll just bet if you research it the speaker was carrying one and it was turned on but set to silent during his speech and likely as not its RF sneaked into the system right at the mic set up by the podium.
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Old August 11th, 2008, 11:16 AM   #3
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not sure it's blackberryitis. They usually (at least in my experience) make more of a staccato type noise. When I first listened it almost sounded like a still camera mirror (film camera) snapping back but after listening some more, it's hard to say what it is. It almost sounded like you had a wireless receiver on the camera and were switching it off and on. But without running a wireless I guess it wasn't that. However I also saw some digital drops in the video so it's is absolutely something electronic.
It may very well have been a blackberry or some other sort of electronic device that interfered with you. It's really hard to be specific but if you have not been able to recreate it it sounds like it was a 1 time anomoly.

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Old August 11th, 2008, 11:19 AM   #4
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It absolutely doesn't sound like GSM/Cellphone interference. Might it be caused by dirty tapehead on your cam? As I see some blocky image defects on the first glitch. Did you run many hours of tape through the event?
I've actually never seen/heard this kind of glitch other than caused by bad mic-cable connectors as are 3.5mm ones but not on a XLR based solution. Are the connections on your cam solid and do not have any play in them?

T
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Old August 11th, 2008, 06:12 PM   #5
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Quote:
Originally Posted by Steve House View Post
Them little crackberrys produce a lot of RF noise as messages come in, enough to even intrude into hard-wired systems. Could have been picked up by the mic electronics or directly in the camera even though you had a balanced cable run. I'll just bet if you research it the speaker was carrying one and it was turned on but set to silent during his speech and likely as not its RF sneaked into the system right at the mic set up by the podium.
Steve; there were about 10 different speakers over the 2 days and the glitch is on about 6 of them. You may be on to something as I went back and analyzed where the the problem occurred. There were 2 speakers who floated around the stage area with a wireless microphone and never got close to my podium microphone. Those speeches were close to an hour and there are no audio glitches at all. Others gave 30 minute speeches and there are 2 or 3 glitches in that time.

Would it have to be a Blackberry that was causing this or is any cellphone a likely problem?

Mark
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Old August 11th, 2008, 06:18 PM   #6
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Originally Posted by Toenis Liivamaegi View Post
It absolutely doesn't sound like GSM/Cellphone interference. Might it be caused by dirty tapehead on your cam? As I see some blocky image defects on the first glitch. Did you run many hours of tape through the event?
I've actually never seen/heard this kind of glitch other than caused by bad mic-cable connectors as are 3.5mm ones but not on a XLR based solution. Are the connections on your cam solid and do not have any play in them?

T
Hi Toenis. Video was captured directly to a notebook hard drive via firewire as well as to tape and audio problem is on both so I have discounted head problems for that reason. All new cable and connectors seemed very solid to me. Disconnected overnight and reconnected for the next days speakers and it is present on both days.

Mark
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Old August 11th, 2008, 06:31 PM   #7
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Sorry but to my ear it's not cellphone or blackberry. I've been saturated with that and they give a staccato type noise not a hard pop like you experienced. A wireless mic would be more prone to getting pinged by the cellphone or blackberry than a hardwire. Not to say it can't or doesn't happen-it has to me but only once that I can think of in the last few years.
Again it sounds to me like something else elelectronic in the arena where the presentation was done-something close to a mic or cable. Pehaps someone was recording on their own for their use and caused the glitch. Honestly if you can't reproduce it I wouldn't worry about it until next time and then perhaps run your audio differently. It sounds like a ghost in the machine. A one time deal and frankly you'll pull your hair out trying to figure it out.

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Old August 12th, 2008, 03:59 AM   #8
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If it's not berry/cell interfrerence got me stumped. Moisture from excessive humidity condensing on a condensor microphone can produce a similar sound but the Sony mic is an electret condensor and moisture problems are usually only a factor with true condensor types.
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Old August 12th, 2008, 04:25 AM   #9
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The experts

Not sure that this is a particularly helpful observation here, but the folks who analyse CVR tapes (the AAIB in the UK and the NTSB in the US) are particularly good at finding out what causes spikes on tapes. They are very thorough and methodical and nearly always manage to solve these anomalies and recreate the effect as evidence.
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Old August 12th, 2008, 08:05 AM   #10
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Sound to me like a momentary "lapse" in phantom power. As this was hard wired, is it possible someone stepped on the cable at that point?

As well, the mosquito noise is interesting as well, as previous mentioned. My experience with drop outs on DV though is that you get nothing and then Doppler like aliasing.
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Old August 12th, 2008, 11:54 AM   #11
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The first glitch seems top be in the picture as well.

My experience says it is not cell phone or radio mic. Could be a light switch or electrical switch of some kind.
Or software problem.
Or tape head.
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