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Old June 10th, 2003, 10:11 AM   #1
Inner Circle
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Location: Albany, NY 12210
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Would this work?

I recently purchased an audio meter from Sign Video, and I?m contemplating the best way to use it. I?d like to split the signal coming out of my XLR adapter, and send one stereo signal to the camera, and one to the audio meter.
Trouble is, the meter runs off of the headphone jack, so my first problem is boosting the mic signal enough. I can calibrate it from there, but I need to boost the signal to about half the output of a typical camcorder headphone jack. Does anyone know where I could get plans for an easy to build circuit that would accomplish this? I?m not afraid of using a soldering iron, but it would need to be a real simple design.
My other concern is ? how risky would it be to split the signal like this? I was thinking about using a Belden 1 foot stereo female miniplug to 2 times stereo male mini plug cord from A2Z cable --


They look like real high quality cables, but is splitting the signal just a bad idea in principle? Will I be risking interference? Will the signal be to weak? I?ve split XLR cables with a Rolls splitter before with no apparent loss in quality, but the Rolls box is ?hard wired.? I don?t even know what that means, other than Rolls claims the signal won?t be degraded.
The point of all this is to be able to monitor the signal before it enters the camera. I have a GL1, and if I plug the meter into the headphone jack, I?m only able to get a reading after the dreaded autogain has already done its damage. I?m betting that with my modified system I?ll be able to give the camera a more regulated signal, because I'll be able to ride the faders on the XLR adapter, and maybe the autogain will have an easier time.
Thanks in advance to anyone who can help me.
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Old June 10th, 2003, 02:23 PM   #2
Join Date: May 2002
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I don't know if you can get where you want to go without the meter plugged into the headphone jack. Does your camera have any audio metering? I'd guess not from your comments. Does line out work while your camera is in camcorder mode? If so, you could use the line-out signal as a monitoring source. Then all you would need is a simple headphone amp which I think you can find already built. The headphone amp would also work with your XLR adapter. You would have to calibrate the system in any case (see below)

Spitting signals may not damage the sound very much but it normally clobbers the calibration of any measuring equipment affected by the split.

You can always recalibrate if you have a variable-gain amp to feed the meter. Then all you have to do is find a calibrated source with which you can set up the variable gain amp so the meter reads correctly.

My experiences with trying to outhink autogain on a Sony Hi-8 camera were not too good. I tried a mixer and a compressor to 'smooth' things out. Didn't really work for me because the sound environment would change so rapidly that I couldn't adjust the equipment fast enough. So in a rapidly changing sound environment, the AGC created the dreaded pumping sound that I didn't want. But I was trying to shoot in a location with model IC engines being run from idle to screaming fast and back again at irregular intervals.

Turned out the only solution was to use a camera that did have manual control.
Mike Rehmus
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Old June 10th, 2003, 11:17 PM   #3
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Location: Bloomington, IL
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You should always monitor what comes out of the camera. It might be great going in but bad coming out and you would never know if you didn't monitor the output. And what you monitor from the camera is what's going to tape.

Splitting the signal will only have a negative impact on it.

AGC on cameras is a bad feature with no good alternative work arounds.

You could buy a seperate audio recording device, run the input to that, and use the meter to monitor the output off of that.
I know that's some extra expense but it would create much cleaner audio than what the agc would give you.

Ben Lynn
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Old June 12th, 2003, 10:30 AM   #4
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Thanks for the responses. I think I got it figured out -- a Rolls PM50sOB. It passes through the signal and has its own headphone jack. I don't know if I would ever use this setup in the field though, as I don't like having a lot of gadgets around with wires everywhere. It's more to help me learn how my camera handles audio.
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