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Old September 3rd, 2007, 03:16 AM   #1
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Question about external mic and windscreen

So, I got this $25 external clip-on mono microphone from Radioshack which I use for interviews that I shoot with my HV20. Should I leave the "Windscreen" option on AUTO, or should I turn it OFF? You see, the "OFF" setting has an icon that shows external mics, so I am a bit confused if I should have this option on or off when I use my external mic.

The reason I am asking this is because a friend of mine said that during the parts of my video where people were speaking ( http://www.youtube.com/watch?v=CXLWMxmQ_84 ), he could hear a "whine", a high pitch noise when the clip-on mic is used. So, I don't know now if the problem is simply because the mic sucks, or because of the windscreen set to AUTO.

Last edited by Eugenia Loli-Queru; September 3rd, 2007 at 03:59 AM.
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Old September 3rd, 2007, 04:01 AM   #2
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It's better to leave the built-in electronic "windscreen" OFF. You'll get better results by just putting a regular physical windscreen/mic muff on your mic and camera.
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Old September 3rd, 2007, 04:25 AM   #3
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I can't use a "muff" on that clip-on mic because it's too small. It goes on the t-shirts. So are you suggesting that I should turn off windscreen even if am not able to use a muff on that particular external mic?
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Old September 3rd, 2007, 05:09 AM   #4
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Quote:
Originally Posted by Eugenia Loli-Queru View Post
I can't use a "muff" on that clip-on mic because it's too small. It goes on the t-shirts. So are you suggesting that I should turn off windscreen even if am not able to use a muff on that particular external mic?
If you ever do want a windscreen on a lavalier, there are these that work well:
http://www.bhphotovideo.com/bnh/cont...arch&Q=*&bhs=t
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Old September 3rd, 2007, 04:00 PM   #5
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Hehe... these cost more than the mic itself. :D
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Old September 3rd, 2007, 06:46 PM   #6
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The little whine (that I could hardly hear) is electrical. Probably just a cheap mic, or inferior shielding on the cable. I don't think it has anything to do with with using or not using a wind screen. Try using an impedance matcher inline (they're fairly cheap).

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Old November 25th, 2007, 09:39 PM   #7
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It was very difficult finding an impedance matcher. I found one, and it had no much description in it. It ended up being XLR to 1/4", instead of 3.5" to 3.5", so it's useless (thank God, it only cost $14).

My lavalier says that it has an impedance of 1000 Ohm, but the HV20's manual says something about its 3.5" input being 600 Ohm and requiring a 5000 Ohm mic. Honestly, this part is not very clear and so I still don't know if my lavalier is suitable for the HV20 or not.
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Old November 26th, 2007, 05:32 AM   #8
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Yeah, the whole impedance thing can get kind of tricky. Your mic (@ 1,000 ohms) should be OK with the Canon, which is a medium impedance input. 600 to 10,000 ohms is medium to high impedance, so 5,000 ohms would be the ideal in-between impedance for the Canon HV20. There are so many things that can cause whines, and hums etc. that are not even associated with the mic or the camera, for instance: a wireless mics transformer plugged into an outlet that's on the same circuit as a fridge or fan or something like that. Have you tried a different mic (not the same kind) to see if the whine is still there? BTW, It sounds like you bought a low to high (high to low) impedance converter (transformer) instead of an impedance matching device. I'm probably just confusing you more. Here is a pretty good page on the subject:

http://www.mediacollege.com/audio/mi...impedance.html
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Old November 26th, 2007, 06:09 AM   #9
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This is the one I bought:
http://www.amazon.com/Whirlwind-Litt...4824044&sr=8-1
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Old November 26th, 2007, 08:30 AM   #10
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A 1000 ohm mic should be fine without any impedance matcher based on an HV20 input impedance of 5000 ohms. The impedance matching thing for mic inputs dates mainly to the old days of vacuum tube circuits and is normally not a significant issue if the impedances are reasonably close, or the input impedance of the camcorder is higher than the output impedance of the mic.

If the input impedance of the camcorder is lower than the output impedance of the mic, you loose more signal level, and the mic may start to distort at somewhat lower sound pressure levels, than if the input impedance is higher than the mic output impedance.

As to whether or not it is better to use the wind filter on - conduct some tests to see which mode better satisfies your artistic intent and needs of the local environment in which you are shooting.

One issue with lav mics is rubbing against clothing. Wrapping it in a layer of nylon stocking may help reduce this noise source.

Note that precise impedance matching is important in situations where the length of the wires is a significant portion a quarter wave length of the frequencies of interest (e.g., over a mile for audio cables, but perhaps only couple feet for broad band video or data).
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Old November 26th, 2007, 04:17 PM   #11
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That's a transformer, converter, always good to have around. It wasn't money wasted. (IMO)

The sound (noise) in question is is an electrical whine.. nothing that would involve a wind screen. (IMO)

Using a variable imp. matcher is basically a way to fine tune a mic, or instrument to a pre-amp input to achieve the optimum performance, and some times sound coloration (EQ), S/N, and noise cancellation. A lot of high end audio gear still builds in variable imp. matching as a feature.

True, the theory goes back to the old Bell day's on long runs of telephone lines, vacuum tubes etc., but is by no means dated technology. BTW, you do not want to match perfectly, there should be about a 10:1 ratio between mic output, and pre-amp imput.

Also true, the 1k imp. should be fine (on paper) with the HV20 as long as it's not (in your words) a crappy mic.

The bottom line is there is an electrical whine. If the whine is there with all mics, then it's the camera. If the whine is there only with your lavalier mic, then it's the mic. If impedance tweaking, and ground floating, and all the old audio "what do we do nows" don't work, then try a new mic.

I'm by no means an authority on the subject, but I do use line matching everyday in my job, and it does make a huge difference, and does help to eliminate a lot of strange noises.
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Old November 26th, 2007, 04:52 PM   #12
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Problem is, I can't find anywhere a 3.5mm to 3.5mm imp. matcher. :o
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Old November 26th, 2007, 11:39 PM   #13
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Probably because impedance matching is a "pro" feature, and pro mics don't generally utilize 3.5mm mini plugs...

You may get better results by running the mic into a portable preamp to boost the signal. A preamp is a solid investment, because it's independent of both your mic and your camera (so it won't become obsolete if you upgrade).
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Old November 26th, 2007, 11:56 PM   #14
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You're probably not going to find anything with 3.5mm jacks, you'll probably have to use an adapter or 2. Can you plug your mic into an audio mixer, then to the HV20 just for a test to see if the noise is still present? One of the guy's in the band should be able to hook you up in a couple of minutes.

One sound company I used to work with ( about 3 years ago) had these little single battery operated boxes with an input / output, and a variable knob, the whole thing was not much bigger than a match box, and they used them to match guitars to amplifiers, and mics ( from direct boxes ) to stage monitor setups. They worked great for all kinds of problem solving.

I'll try to track one down for you. I think this thread is beginning to go beyond the scope of your original question :)

Also, I keep forgetting that we are talking about a $25 Radio Shack mic. It be easier all the way around to just go to a Camera or Music store with your camera, and try a few mics, go home, and compare them close up.
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Old November 27th, 2007, 12:45 AM   #15
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Thanks, yeah... I think I will buy that lavalier stereo mic from Sony. It's the only one that's stereo and only costs $35.
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