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Sine wave hum at approximately 400Hz, 1.2KHz, 2.1KHz

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Ryan Mast
Sine wave hum at approximately 400Hz, 1.2KHz, 2.1KHz
on Sep 8, 2010 at 8:18:30 pm

A couple weeks ago on the shoot, I noticed an odd hum in the audio monitor on my JVC HM700. Here's what it looks like on the spectrum (zoomed in):



Has anyone else noticed this? I only started noticing when I set the audio gain to about 8 or higher. It's a known good mic & cable, and I get the same with other mics/cables, too. Is this normal for this camera? Anything I can do about it?

--
Meteor Tower Films
We make music videos, design video for live theater, and build interesting contraptions.


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Phil Balsdon
Re: Sine wave hum at approximately 400Hz, 1.2KHz, 2.1KHz
on Sep 8, 2010 at 9:19:02 pm

I had a similar issue a couple of weeks back.

Shooting chroma key with two cameras and 2 angles, JVCs a 111e and a 251e. The director wanted to see the keys live (but do the actual keying in post) so hired in a keying system. Video was output from both cameras to the keying hard ware which was mains powered.

Audio recorded on the DR HD100 drive (Quicktime mode) on the 111e had the same issue you are seeing. It was not on the taped version, so therefore not a flaw in the incoming audio. We put it down to earth loop hum from the mains power to the keying hardware which was connected to the camera with a video cable.

Normally I work with a battery powered external monitor. Did you have some kind of mains powered device connected to the camera? Never seen it before on this JVC camera, but have the issue on other cameras in the past being powered by an external transformer.

Simpler explanation might be some kind of radio frequency interference at the location.

Cinematographer, Steadicam Operator, Final Cut Pro Post Production.
http://www.steadi-onfilms.com.au/


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Ryan Mast
Re: Sine wave hum at approximately 400Hz, 1.2KHz, 2.1KHz
on Sep 11, 2010 at 9:26:24 pm

I'm getting the hum in the recording with AC adapter power and with Anton Bauer battery power, in different locations on different sides of the state -- any other environmental factors I should test?

--
Meteor Tower Films
We make music videos, design video for live theater, and build interesting contraptions.


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Phil Balsdon
Re: Sine wave hum at approximately 400Hz, 1.2KHz, 2.1KHz
on Sep 11, 2010 at 10:15:43 pm

Maybe you've tried all this but change all audio kit connected to the camera, cables, mikes, headphones.

Disconnect external monitor or anything running mains power. Turn your mobile / cell phone off.

If it still persists you may need to take back to JVC for a solution.

Cinematographer, Steadicam Operator, Final Cut Pro Post Production.
http://www.steadi-onfilms.com.au/


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