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Old January 24th, 2006, 11:26 AM   #1
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Xl1s Full spectrum hiss?

I'm getting a full spectrum hiss through the head phones recording or not, tape or not. I would like someone to help me test this if possible...could you disconnect all audio input, crank up the mic level and listen through your headphones.

I'm having to turn up the mic gain to get any signal from my ATR55 to come through and it's adding hiss.

The mic through my wireless system provides spotless sound. I've switched out cables and added ferrite cores to the ends of the cables, made sure I don't get near any power sources/lines.

I've tested down to the point where I disconnect all audio inputs and turn up the gain and it still hisses. I'm curious if it's just my camera or if other Xl1s's exhibit the same behaviour.
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Old January 24th, 2006, 11:38 AM   #2
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I should have read deeper, aparently this is a common problem with the Xl1 cameras... has anyone found a way to get this to work well and cheaply (read: parts from radio shack and some time soldering)?
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Old January 24th, 2006, 04:54 PM   #3
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I found this online:

http://tangentsoft.net/audio/cmoy-tutorial/

DIY pocket headphone amplifier. This should help boost the voltage going into the camera allowing me to lower the gain and eliminate the hiss.
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Old January 24th, 2006, 05:30 PM   #4
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I've previously run test on XL1 audio noise levels. The noise floor of the baisc XL1 is actually quite low for a camcorder. Baring a defect in your unit:

The ATR55 mic is a decidedly consumer product and is the likely cause of your complaint. It has a relatvely high output impedance (2200 ohms in tele position) and low output (-45 dB at 1 Pa), making it a poor match for the XL1 (which has a 600 ohm input impedance). At its budget price point and give that TA does not publish a noise specification, I suspect it has a relatively high noise output as well. Private label versions (e.g., SME ATR55) have a signal to noise ratio of around 40 dB - rather poor. A good mic should be around 70 dB or better.

Also monitoring though headphones tends to exagurate any hiss/noise in the audio stream. If you try playback the video tape thorugh a normal viewing medium such as a TV you will probably find that in a typical viewing environment the noise is not anywhere near as apparent.

The impedance mismatch alone results in about 13 dB loss relative to the open circuit output of the mic, and thus requires more gain in the camcorder, making the nosie in the camcorder preamps more apparent relative to the desire signal.

The headphone amp will boost the signal to your headphones, it will not help the signal recorded to tape.

I believe that your best bet is to obtain a quality microphone designed for use with 600 ohm inputs. (Why use a $50 mic on a $3500 camcorder?)
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Old January 25th, 2006, 08:07 AM   #5
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I'm going to use the headphone amp as a mic pre-amp.

The hiss is quite noticeable in the editing suite as well.

I'm not using a $50 mic...had it been full price, I'd be using the onboard mic ;)...I found it on sale for $25. I spent all my money getting the camera (used btw).
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Old January 25th, 2006, 08:38 PM   #6
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The key issue with microphone preamps is to use very low noise components. To obtain good signal-to-noise performance, the preamp's equivalent noise input at the preamp input terminal needs to be around a millionth of a volt or less. Headphone amplifiers do fine with noise levels 100 times or more greater. While I have not check the specs of the headphone amp you are planning to build, I would be very surprised if it provides satisfactory service as a mic preamp.

I would expect the XL1 standard mic to do as well or better than the ATR55 in the nosie department. The downside being it has stereo cardoid pattern if you need a shotgun pickup pattern,
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Old January 28th, 2006, 07:11 PM   #7
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I'll be talking to an EE on this one for help to get precisely the solution I'm looking for. I'm low budget, but I go all out on it! I will be keeping component quality in mind while redesigning the headphone amp to work in this application. Thanks for the warnings about the stray input voltage tolerances. Right now though, just about anything would be better than what I'me getting.

Given money, I could solve this in a heartbeat by upgrading to a better microphone, but that's not an option for me. I do get better audio out of the built in mic...but not from the distance I'm placing the camera to fake shallow DoF, and certainly not in the windy environs that we've been shooting in almost every day we step out the door...murphy's law is real, I've seen it.
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Old January 29th, 2006, 10:18 AM   #8
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At what distance are you shooting? Consider making an extension cable for the built-in mic so you can get it closer to your talent (within a couple feet is best for voice). Closer gives more volume at the mic and reduces the effects of wind and other ambient sound relative to the talent.

Last time I looked the necessary parts wer available at Radio Shack - a 3.5mm stereo mini phone plug and jack (for audio), and a 2.5mm sum mini mono phone plug and jack (for power), and wire. You should be able to go 20 feet, probably more, without significant problems in most shooting environments.

Keep in mind that not all EEs are into audio or sound systems.
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Old February 5th, 2006, 09:59 PM   #9
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Solution...duh!

I should have kept thinking more simply, I solved this with $8 in parts from radioshack...no soldering required! Posted here.

http://www.dvinfo.net/conf/showthrea...631#post425631
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