60hz hum when using microphone boom?? at DVinfo.net

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Old March 6th, 2006, 04:53 PM   #1
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60hz hum when using microphone boom??

I'm shooting a documentary on the Canon XL2 and I've run into an interesting problem that I can't find any information on. When I'm recording using a 20 foot cable on a microphone boom, I end up with what sounds like a 60hz hum on the final audio output. This is not audible through the headphones during the recording. The only way to avoid this is by using the battery which incidently only lasts one hour. Any suggestions?

David Parish

Last edited by David Parish; March 6th, 2006 at 06:28 PM.
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Old March 6th, 2006, 05:04 PM   #2
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I just went through the same issue this past weekend, never fun. If you've been able to avoid it by shooting on battery power, I'd stick to that and buy/borrow another battery. Other than the AC adapter and the XLR cable, is there anything else connected to the camera like a BNC cable or other devices?
You mention it isn't audible through the headphone out and that sounds strange to me - could it just be at too low a level to hear? sometimes turning the headphone out volume all the way up will reveal these nasties.
hope this helps
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Old March 6th, 2006, 05:23 PM   #3
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Nothing else is connected to the camera. Initially I assumed it was something like too much resistance on acount of the length of the cable but when it disappeared with battery power, I knew something else was going on. The headphones are turned up about 75%, plus I have some volume control on the headphones. I hear nothing out of the ordinary while recording but it is quite loud on playback.

David Parish
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Old March 7th, 2006, 10:47 AM   #4
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This may be more of a solution for the bad audio, but have you thought of using something like SoundSoap (I think is what it's called) to clean up the audio track? I don't know if it will work for the issue you have, but apparently it's pretty good at correcting audio problems. You may even be able to download a demo to see if it will work.
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Old March 7th, 2006, 11:14 AM   #5
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Thanks for the suggestion, I'll look into this as an option.
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Old March 11th, 2006, 02:38 AM   #6
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You need to turn off the refrigerator before shooting. I kid. Maybe it has something to do with the playback setup or perhaps a bad cable. 60 cycle hum is usually a byproduct of difference of ground and since both your battery and ac adapter supply dc power to the camera and mic it is interesting you should have it. The ac adapter has only hot and neutral prongs. Is the boom going straight to the camera or is it post mixer? If it's post mixer that's your problem.
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Old March 18th, 2006, 09:47 PM   #7
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The boom goes straight to the camera. The cable is a bit long (20 feet) but works great with no apparent loss in quality when I use the battery. I took some earlier advice and got a second battery until I can figure this out.
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Old March 18th, 2006, 10:00 PM   #8
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Shielding....

It just may be the cable. With use, cable shielding can wear away ( this is usually due to stress on the connector or constant tension, or just a manufacturing defect). If the shielding on the cable is bad, radio waves, RF from the camera, heck even the boompole can cause hiss or hum.

For instance, on a SP shoot, when we plugged in the cable from the boom op to the camera, we got an audible hum. We found that the headphone amp box, clamped onto the aluminum boompole, caused the faulty wire to hum. The cable was switched and all was well.

As stated before, sometimes the can just might not be turned up enough to hear the hum.

Switch the cable and see what happens.
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Old March 19th, 2006, 04:39 AM   #9
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I would second the idea of switching the cable. A proper balanced connection should have excellent hum rejection, even with a 20 foot antenna.

Richard
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