Hi John--
Some distinctions start to show up only after years of monitoring the
recordings.
Below is my tedious and rather obvious comparison test method I've
used. (I have no test gear I can trust more than my ears). When I've
finished, I've been satisfied that I've found the best matched pair.
I get together my best stereo pre (744/722), my best pair of
headphones and four matching length/brand cables. I place all four
mics on stands in the middle my largest, quietest room facing in the
exact same direction. I place the diaphragms of all four mics
together as physically close as I can get them.
In the wee hours (monday am is often best), I go around and turn off
everything. I place one clock directly in front of the mcs and a
boom box about 4 feet away. Everything must be away from the walls. I
run the recorder on battery power.
I set the recorder pre gain at max or near max and match the left
right input levels with a soft 400Hz sine tone. You can generate this
signal with free apps like sigjenny or test-tone and play back it
back on one speaker of the boom box. Use the signal from one mic to
set the same level on both mic pre channels using the LED display.
I make these recordings running the recorder until the local ambience
has "settled" to a minimum for at least 10 seconds-- no close
traffic, no refrigerators, etc- Sometimes the takes have to run as
10 minutes before this happens. A long time to sit quietly.
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