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Old January 12th, 2005, 11:58 AM   #1
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Join Date: Nov 2004
Location: Houston, TX
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Testing Used Mics

Greetings all:

I'm looking for suggestions on how to test a newly acquired USED mic to verify that it is still operating properly (hopefully like new :) ).

I just bought two used mics:
Audio-Technica AT825 Stereo field recording mic
Audio-Technica ATM31a Cardiod Condenser Mic

The ideal solution would be a procedure and software that would analyze test recordings.

The only hardware I have available is my camera (GL2) and computer.

Any ideas?

Pete Wilie is offline   Reply With Quote
Old January 12th, 2005, 11:13 PM   #2
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How about your ears. low tech, but it works.
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Old January 13th, 2005, 09:23 AM   #3
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Can't Trust MY Ears

Hey Bryan,

Well, maybe :)
You don't know my ears :)

Seriously though, testing/listening is the first thing I do, of course!
But, I don't have the trained ears of an audio professional, nor do I know exactly what range/type of sound should be the source for my test. And finally, since I purchased these mics used, it would be difficult at best to try to return them claiming "it doesn't sound good enough".

But most importantly, I want to verify the mics will perform as designed BEFORE I use them on a production shoot, which will often be an event that can't be re-shot.

So, I'm looking for a more definitive test/analysis procedure.
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Old January 15th, 2005, 11:56 PM   #4
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Generate some white noise or whichever produces all frequencies, record some noise in an acoustically dead space and then analyse the signal with software. I did see something like an audio ossiloscope for Mac, but can't remember the name. That's what the mic manufactures do anyway, you won't get close but it might give some indications. You could test it out with a known good mic that you have a curve for then you might get some ideas.
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Old January 16th, 2005, 06:00 AM   #5
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Programs like Audition (formerly Cool Edit Pro) contain white-noise generators and frequency analysis capability.

You could play white noise (even FM inter-station noise) through a good Hi Fi system, record and see how the recorded signal looks. of course, this test also include the quality of the HiFi and the room acoustics. This is useful only if you have other mics to check it against.

Some things to look for that may be a bit easier:
Do they look unusually dirty, beat-up, or abused.
Do conenctors insert/remove easily?
Any evidence of a battery leaking in the mic?
Do any switches appear to work/have the intended effect, e.g., low frequency roll off on the AT825.
Are cables provided?

Are the channels (on the stero mic) balanced - i.e., have about the same output level for a sound source in the middle and at 45 degrees off axis in either direction.

With the mic in a very quiet room (and burried under a lot of soft pillows), is the base noise level from themic low.

Expect the ATM31a to have about 3 dB more output than the AT825

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Old January 18th, 2005, 09:57 AM   #6
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audio software

I suggest you try this site http://www.faberacoustical.com there are a couple of excellent applications to first generate different test signals and also to analyse the result in huge detail. I have used it a lot to check noise floors in gear.
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