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Canon XL and GL Series DV Camcorders
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Old January 7th, 2005, 06:13 PM   #1
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Mic Att question. LitePanels troubles?

Okay, I got the LitePanels LED lights about 3 weeks ago. Upon hooking up, I noticed a very annoying, zipper-like buzz in the audio when the light is on. As soon as it's moved 3 inches away from the on-camera mic, the noise goes away. I contacted LitePanels about it and they sent me a new one. Same deal.

(By the way, they were quite prompt and courteous and got me the new one overnight. Good service.)

I noticed that when I turn on the Mic Attenuator, the noise goes away, but of course it significantly decreases the audio signal, as well. Do most of you leave the Mic Att on or off?

By the way, without the extension arm for the LitePanels, it also prohibits you from popping up the viewfinder to use the LED. Argh...I wish the extension arm was affordable and all of these problems would go away.

Thanks.

Kevin
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Old January 7th, 2005, 07:55 PM   #2
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Hi Kevin,

I looked up the LitePanels on the 'net -- wow, nice but not cheap! This is only this hobbyist's opinion, but at that price I wouldn't be very happy about a buzzing sound in my audio no matter the light output or customer service.

My first thought was 60Hz hum. It could also be an actual noise from the powered hardware, though. Were you using AC power? Can you actually hear a buzz if you put your ear very close?

It's all well and good that mic atten helped, but seems you shouldn't be forced to use it. My limited understanding is that mic atten will help when there is background sound -- such as HVAC or like you have now with this buzz -- that you can't get rid of ... it reduces the efforts in post at the cost of some dynamic range (I think). However, if you have a pristine sound environment, you wouldn't want the mic atten.

Audio experts, what do you folks who really know sound have to say?
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Old January 7th, 2005, 07:58 PM   #3
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Exactly my thoughts, Pete. For that price, this thing should work perfectly and I should not be forced to pay an outrageous $200 extra for the extension arm. They are being good about this so far, so we'll see. It seems to give a buzz on both the XL1s and XL2. Neither is an external sounding buzz...just an audio interference buzz that is being recorded to tape.

Any more info on people's use of the Mic Att would be appreciated.

Thx.

Kevin
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Old January 7th, 2005, 10:01 PM   #4
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Hi Kevin. The Mic Att is for use when you are in a very loud environment, where a high mic output would overload the camera preamp. If you use this in a "normal" environment, the record level will need to be turned up to compensate for the reduced mic signal. The end result is that you will get the same recorded level, but with additional preamp noise.

Whether it also helps to reduce the hum from your lights depends on exactly how it is being coupled into your camera's audio system (e.g. acoustic pickup by the mic, EMI coupling into the mic cable, EMI coupling into the preamp). My gut feel is that it probably won't help.
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Old January 7th, 2005, 10:36 PM   #5
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Thanks, Richard. That's what I suspected, but wanted to make sure that most people leave "Mic Att" OFF unless in a concert or other very loud setting.

Looks like they need to comp me an extension arm for this light to get rid of the buzz.

Thanks.

Kevin
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Old January 8th, 2005, 12:30 AM   #6
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led are not driven by continuous voltage but by a square signal at high frequency (that what allows to dim the panel). such high power pulses can interfer with your sound input .
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Old January 8th, 2005, 03:04 AM   #7
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Yes, but the website says "flicker free". I was wondering about that...
I just built a led light that uses constant current circuit that doesn't pulse. Higher effiency versus slight color shift is the tradeoff. Pulse Width Modulation has no color shift (why would it since the leds are powered at the same strength just diffrent timing).
Something you might try is to see if there is any change in the hum when you dim the light. Probably won't be if the timing stays the same. Maybe litepanels can add some shielding on future versions.
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Old January 8th, 2005, 06:10 AM   #8
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I believe Richard M. has pointed out the source of your problem. There will be no 60hz hum as the lights are not AC powered. However, the dimmer is exactly as was described. They vary the duty cycle of a square wave to achieve the effect. This would easily produce the 'zipper' type sound that was described. It sounds like Lite Panels need to incorporate some better shielding into their design, especially since the effect is present on two different camera models.

Kevin, how is the lite unit powered? Does it use its own battery power? If so, then the noise is being radiated out of the casing. If the power is being supplied through a tap from the camera battery then the noise could be getting coupled into the interconnecting wires. The former would require better shielding of the casing, the latter would require some de-coupling capacitors from power to ground to shunt the noise to ground.

Because the shoe attachment is so close to the mic cable, I suspect the unit is radiating noise into the mic cable. Since that cable is an unbalanced connection, it would be susceptible to induced noise from a nearby source. If you could use or borrow a mic with XLR and plug into the rear jack on the XL2, I bet your noise issue won't be there. The XLR will cancel out the noise.

By the way, by 'flicker free' they mean that the switching frequency is high enough that it won't present an issue with video sync the way 60hz lights can. Since the duty cycle is all that changes, you won't hear a different 'pitch' when you operate the dimmer, you would hear a different 'timbre' or tone.

Sorry to be so long winded, but I would contact Lite Panels about this issue. They need to address their design flaw.

regards,

=gb=
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Old January 8th, 2005, 09:10 AM   #9
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usually PWM is much higher frequency than 60Hz (probably around Khz).
If the PWM is produced on the panel, it is possible there is a leak on the heatsink that support the high power transistors.
if it is produced into the remote power supply, the power supply cable makes a good antenna.
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