It's probably worth of noting that those NT-1A's, like all large
diaphragms, are very sensitive to pressure gradients at low and
ultra-low frequencies. You can get waves like the ones in your
screencap just by waving your hands close to the mics. In
practice, they're are often of shorter duration, because the
mics are getting just enough wind to cause an intermittent
problem, but not enough to make it obvious that wind protection
is needed.
With the waterfall, perhaps there was just so much LF that the
preamp overload was constant, and reasonably periodic. I missed
a few msgs in this thread, so perhaps I'm off target, but it
looks like you need a combination of good wind protection (at
least foam) and some LP shelf. With just foam wind protection,
my NT-1A's do pretty well in moderate breezes. With real "wind,"
though, you have to build a hairbag...
I prefer, of course, to record without anything covering the
mics, but it's interesting how imperceptible air movement (in a
sense they're ultra-LF pressure waves, even as low as 1 Hz) can
produce occasional mild flapping or dimpling of the diaphragm,
which can masquerade as inexplicable clipping, or an
intermittent connection, or a flakey pre.
Hope this helps...
ac
Allen Cobb
http://timbreproductions.com
-----Original Message-----
From:
Behalf Of John
Hartog
Sent: Monday, January 23, 2006 3:11 PM
To:
Subject: Re: [Nature Recordists] Bottoming-out revisited
Thank you Rob, Klaus, and Eric for your comments - all very
helpful.
For me, not having a formal background in audio beyond this
nature
recording hobby, I am slow to grasp some of the technical
concepts.
So, thanks for taking time to reiterate once again.
Rob, you wrote:
>This happening with another PIP mic on HiMD could be consistent
with
>Curt's theory that something is going on with high level in
using
>PIP power on the HiMD mics pre.
Perhaps it's the PIP, but recall last time this came up Curt
Olsen
reported the problem still occurring when he powered the mics
externally and using the line-in. He also reported an
inline -10db pad
did not help either. However, he did suggest that using a Sound
Pros
SP-SPSB1S battery module with bass roll-off did correct the
problem.
Klas's suggestion of -20 db attenuation before the input of the
recorder is worth trying: perhaps the -10db that Curt tried was
just
not quite enough. What size resistors would I need, and where
should I
connect them?
Regarding, the PMD-670/NT1-A's clipping.
Back in October, Allen Cob mentioned a similar problem clearing
up
with the low shelf enabled.
Back in Nov 2004, when I first posted about my clipping problems
with
the pmd-607 and NT1-A's, one group member contacted me off list
to say
that he had called Marantz regarding a similar problem while
trying to
record waterfalls.
Reportedly, Marantz Tech Support recommended that for the best
possible recordings:
1.) Put the Level Control Switch on Limiter
2.) Turn the Record Level wheel to its highest setting, 10
3.) Change the Algor/File Settings to: Stereo, MP3, 48.0 kHz,
160 bps, mp3
4.) Set the MIC ATTEN switch to -20 dB because the Rode mics are
sensitive.
The advice apparently worked for him.
I tried most of that except for changing to mp3, but it didn't
really
help things for in my particular situation of trying to record a
20
foot ocean swell crashing into a spot called Devils Cauldron.
Since
the HIMD/Rolls/NT1-A arrangement seems to work better than the
pmd670
in loud bass environments, I'll just stick with that next time
around.
Eric, I admire that you are working on recoring the surf while
surfing. I'm a surfer too, so I know the dilemma of having to
choose
between surfing or nature recording when the winds finally calm
down.
Yesterday I chose to surf. I'll be interested to know how it
works
out. I'm imagining a waterproof Dan's Vest.
-John Hartog
"Microphones are not ears,
Loudspeakers are not birds,
A listening room is not nature."
Klas Strandberg
Yahoo! Groups Links
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