>If you want binaural, then try a Jecklin disc kind of setup, rather than
>spaced omnis. Keep your mikes about 6.5-7 inches apart, simulating the ear
>spacing of the human head. This will yield a fairly decent binaural
>recording.
>
>http://www.josephson.com/tn5.html
>
>As I mentioned the other day, I dragged a pair of Crown GLM-100s out of
>long-term storage and am getting reacquainted with them. These are
>really impressive mics. To my ear, they seem to perform best in free
>space (with respect to boundaries) and with no barrier of any kind
>between them. Would anyone here disagree with those findings or have
>any additional comments regarding boundaries/barriers and omni mics of
>this type (similar, I'm guessing, to the Sure 183s)?
I was curious about the GLM specs when you mentioned them before.
GLM-100/100E
Open Circuit Sensitivity:
GLM-100: 3.2 mV/Pa*(-50 dB re 1 volt/Pa*).
GLM-100E: 8 mV/Pa* (-42 dB re 1 volt/Pa*)
Equivalent Noise Level: 28 dB SPL typical
(0 dB =3D .0002 dyne/cm2), A-weighted.
S/N Ratio: 66 dB at 94 dB SPL.
Shure MX183
Open Circuit Sensitivity (at 1 kHz,MX183: -27.5 dB (42.2 mV)
Equivalent Output Noise (A-weighted) MX183: 20.5 dB
Signal to Noise Ratio (referenced at 94 dB SPL)
MX183: 73.5 dB
The 100E has more output than the 100. Spec-wise, the 183 exhibits
less self noise and higher gain (sensitivity).
>
>As to spacing, I reported my first impression that there was a nice
>"sweet spot" at approximately 26 inches. But now I feel that that
>spacing presents an unnaturally wide image (I like it, but it seems
>unnatural to me). With the particular pair I have, 8.5 inches seems to
>be yielding the best compromise between width, "naturalness" and mono
>compatibility. Anyone here willing to share their own experiences with
>spaced omni pairs? In particular, I'm wondering if the size of the
>sound source makes a big difference (for example, indoor point source
>vs. "all outdoors"). My goal here is a relatively simple
>stereo/binaural array with these mics that will deliver nice results in
>most field recording conditions.
Your observations about sweet spots seem right on. I'd add that
spacing/stereo imaging depends on immediate and long term playback
systems you're recording for. No spread meets all needs. Does one
spread meet more needs? There's a section in Bernie's book, Wild
Soundscapes" (pg 149-50) drawing from Lang's research that is
excellent regarding binaural playback issues.
The most reproducible stereo imaging scenario might be recording
strictly for headphone playback. A hinge in the middle of two ~12"
extension arms allows one to adjust the spread from 1-26" and find
sweet spot(s) for every situation. I have a 8" X 8" piece of foam
core to use as quickie Jecklin-like divider for the < 8" range. This
is the only way I've ever felt the listener can hear a very similar
field to that I hear in the field if they use headphones.
Then there's polar pattern. Omni-directional mics have greater
high-end response to sources that are directly in front of the
capsules (though much less pronounced than with cardioids). For
recording "wrap around space," mounting the capsules so that they
point away from each other tends to work better than the typical A/B
"front" facing. The later is used when a portion of the field is of
greater interest. Birders, for example, might like A/B front facing
better.
For "typical" stereo living room playback, room
architecture/furnishings often dictate speaker locations. Some people
experiment with placement options, but they're probably using tight
field music when they adjust to taste. When we start guessing what
omni mic spreads will work best for living rooms, it might be
realistic to account for speakers that are too close (within 3') and
way-too-far-apart, like in the corners of a large room.
Perhaps the only way to know you're using a fixed spread you like is
to make a test recording of a large, outdoor setting using several
spreads without a divider. Then make additional recordings of front
facing events like a bird call, a person speaking at 4' and even a
small, close object. Record all of these with different mic spreads
and the closer objects with and without a divider. Play them back
through too-close and too-far speaker spreads.
You might notice that with field recordings (which are typically much
drier than produced music) exaggerated timing differences can give
the listener more clues to assemble "space" with when playback is
through speakers.
Note that if you find yourself enjoying a larger mic spread, the
greatest timing differences are created when sources are directly in
front of one or both sides. When there is a single object or objects
on both sides, by twisting the axis, these sources move towards the
center and the timing difference(s) can be adjusted, even reduced to
that of ear spread. Rob D.
>Thank you in advance,
>
>Curt Olson
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
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