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Testing Mic Pairs (was modified ambient recording setup AT 3032

Subject: Testing Mic Pairs (was modified ambient recording setup AT 3032
From: "Rob Danielson" danielson_rob
Date: Fri Nov 30, 2007 10:10 am ((PST))
  "therebesandinmypants" <> wrote:
>1) how would i go about testing each mic to make sure they match?

You might find that you can hear significant differences more quickly
and more informatively than testing them with tones and wave forms
etc. I set the two mics side by side in an open, quiet location at
least 6 feet off the ground and near no walls. Preferably outside.
This will provide a realistic broadband source.  I use a 2-3 pair of
my best headphones for reference; they should be good ones. Slowly
raise the volume from off to full or almost full while listening for
elements or "bands" that are audible on one side more than the other.
Repeat the fade-in process over and over. Parts of the frequency
spectrum that are louder will shift slightly from dead center towards
the corresponding ear/mic.  This should reveal the glaring
differences. If you focus your attention carefully, you should be
able to judge 3 - 5 ranges of the spectrum such as: the lowest bass;
the low-mids "deeper roars", the mid-range "tinny" the highs
"edginess," "shrillness" or "bite"  and the highest frequencies
"zizz".    Every time you think you hear an frequency emphasis in one
ear that is not in the other, test to determine if you can hear the
same discrepancy with another pair of headphones.  An emphasis in one
mic can actually be a de-emphasis in the mic, but we're only looking
for a performance "match" not perfection.

If you find something that concerns you, place the two mics side by
side in an open space pointed directly at a high quality speaker
about 2-4 feet away. Play and record a sweeping sine tone from 10Hz-
to 30K.  There are free sine tone generator applications on the web.
I prefer sweeps that are about 3-6 seconds long. Look the recording
digitally and compare the amplitude of the two channels in a wave
form.  You might be able to see the imbalances you heard.  Rob D.


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