what is the difference between mic Attenuator and Sensitivity? at DVinfo.net

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Canon XH Series HDV Camcorders
Canon XH G1S / G1 (with SDI), Canon XH A1S / A1 (without SDI).


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Old August 22nd, 2007, 11:15 PM   #1
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what is the difference between mic Attenuator and Sensitivity?

Does ATT only reduce input level? Thanks.....
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Old August 23rd, 2007, 07:51 AM   #2
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ATT position reduces the gain (level) at the mic preamp by 12 dB (for the internal mic) or 20 dB (for an external mic). This reduces the likelihood of overloading the preamps and thus clipping the input signal when you have high input level as from a hot mic and/or shooting in a loud venue.

Because the ATT setting reduces the preamp gain, it also improves the noise floor of the camcorder mic input. That is, the amopunt of hiss induced by the camcorder mic preamp will be lower when using ATT setting than when using the MIC setting. However, to take full advantage of this lower noise you need a higher output from the mic, other things being equal.

Check http://www.dvinfo.net/conf/showthrea...light=mic+gain for more information on the A1 noise at various gain settings.
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Old August 23rd, 2007, 09:58 AM   #3
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My short answer: Always use MIC ATT if you can do so without pushing gain over 80% or so.

My long answer:

A $50 five year old minidisc audio recorder will produce better audio than any video camera under $10K.

The problem is cheap pre-amps, and it can only be properly solved by using a mixer or external pre-amp. Neither of these solutions is really practicable in the run and gun world of videojournalism.

Fortunately there are a couple of settings you can configure in camera to boost the signal to noise ratio and mitigate the problem.

First switch off the AGC (automatic gain control). THE AGC is the most common cause of noisy audio. Sure it will prevent most clipping but it will also significantly boost noise levels, particularly in quieter segments.

Set the levels manually so that the signal is peaking around -12db. In the digital world 0db is the ceiling - go over that and and the audio is unusable. The -12 db setting should give you enough headroom to cope with variations as the subject moves closer to the mic etc.

Check the volume control. The sweet spot for the pre-amp on most cams is in the 30-50% range.

If the volume control is pushing towards the half-way mark or is over it then switch on the attenuation, “MIC ATT”. This will cut the strength of the signal but providing you can keep the gain pot (volume control) below 75% it will improve the signal to noise ratio, giving you noticeably cleaner audio.
Using a hot mic like the sennheiser me66 I just about always have attenuation switched on.

An extra level of protection can be added by sending two different levels to the 2 audio channels. So channel 1 gets a feed with peaks set at -12db and channel 2 at -18db. That way if channel 1 does clip you just switch over to the audio from channel 2.
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Old August 23rd, 2007, 10:41 AM   #4
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Definitely great answers from both of you. The only time I would use the agc is for an interview where the person is not a good speaker and their volume is all over the board. Of course you potentially get a little more noise, but a good noise reduction plugin always fixes that. Most times, if you are running a low music bed, you never hear it anyway... AGC is never good for loud situations ie: clubs and concerts. Even though the meter looks good, it always turns out distorted and the low end is terrible!

Because I do a lot of video for bands and find myself practically in the FOH speakers, I bought an external mic with built in att. Personally I'd rather handle that in my microphone than in my camera. If i get too close to the subs, the mics built in LF roll off takes care of that. Like you said, the preamps aren't that great, so I want the camera to handle as little as possible.
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Old August 24th, 2007, 12:40 PM   #5
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> Of course you potentially get a little more noise, but a good noise reduction plugin always fixes that.<

"Always" may be a bit too strong a term. My impression is that noise reduction plug-ins are a mixed blessing, and can quickly add artifacts if not applied carefully. Better to start with now-noise audio.

The AGC in the Canon prosumer camcorders has been significantly less intrusive compared to that found in consumer camcorders. But for audio level management, it may be better to apply compression in post. AGC probably works best if the the average audio input level is near full gain on the AGC. That way it is not pumping except to limit audio peaks/loud passages, so the noise floor remains fairly constant during normal to quiet periods. If relying on AGC to reduce gain all the time you are wide open for the AGC pumping artifacts.

With peak-indicating metering as with the Canon, you can probably allow peaks higher than -12 dB with most program material without getting into problematic clipping, but let experience with the program material be your guide.

Has anyone run tests on a $50 MiniDisc recorder?.
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Old August 24th, 2007, 01:14 PM   #6
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Don - Jay Rosen is the man who did the testing. Do they still make MDs? My reference was to a 5 year old (ie used) recorder.
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Old August 27th, 2007, 08:33 AM   #7
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http://www.minidisc.org/index.php for latest news on MiniDisc format.

Sony still offers media, and some recorders/players; e.g., the MZ-M200.

I do not know if prerecorded media is still available.
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Old August 27th, 2007, 10:10 AM   #8
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How can I setup dual-mono recording with the 3.5mm jack but not XLR?

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Old August 27th, 2007, 12:44 PM   #9
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Quote:
Originally Posted by Taky Cheung View Post
How can I setup dual-mono recording with the 3.5mm jack but not XLR?

Thanks
You should be able to plug in a Y cable with a stereo plug into the camera and two mono jacks for two mini plug mics. But there doesn't seem to be a way to split the volume control for the L & R signals.

The camera is not setup for using the on-camera mic or the mini-jack differently than on any of the consumer cameras. Many (including me) would like to record one track with the on-camera mic (or the mini-jack) and a second track with an xlr input.

You could use a mixer with a stereo output you could send to a mini-plug, but than that kind of defeats the idea of using the little mini-jack.
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Old August 27th, 2007, 12:47 PM   #10
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Jack, I sort of figure that out. But I have hard time finding that Y-cable. I tried several local radio shack store and couldn't find anything. Most of the plugs there are for stereo to stereo. Do you have any web link pointers I can find that Y-cable online?

I would like to setup that to record 2 audio tracks, one using a shotgun mic and the other is a regular mic. It always safe a lot of hassle in post to have an additional audio track.

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