Thanks again, David. I'll reply in-line:
On 3/11/2010 6:12 PM, Kawika wrote:
>
>
> Hi Robb, I uploaded to files a brief mp3 comparison between raw and
> mangl.. er, processed recordings, titled "Hump for nr"
> http://tinyurl.com/y9kja2m <http://tinyurl.com/y9kja2m>
>
The comparison is enlightening. The edited version is certainly an
improvement. I'll speculate that all of that low-frequency rumble is
from vibrations in the hydrophone induced by cable strum. This happens
when the hydrophone is towed. Were you drifting substantially on the
wind? If so, maybe more of the noise that I attributed to invertebrate
critters is surface noise from small wind waves. Bobbing up and down
and drifting with the ocean swell can do this as well. Low-cut filters
are a blessing at these times.
>
>
> I listened to your "recording that I made last year while sitting in
> a kayak just a few meters over a reef in Hawaii"--astounding! For me
> the question is begged, Where are the snapping shrimp?
>
I wonder if you clicked on the wrong flash player. The environmental
noise is pretty significant. It is the second one under the heading
Robb Nichols, Aquarian Audio - Miscellaneous. The direct link is here:
http://www.aqaud.com/Cust_files/audio/AqAud_humpbacks_reef0209.mp3
>
> if you were only a few meters over a reef. Or were the Humps so loud
> that the shrimp receded into the background? My reason for going out
> in the kayak of course is to escape the shrimp.
I'm not the naturalist that I wish I were, so I don't really know what
is making these noises. If anybody does, I'd love to hear. But I don't
think it is shrimp. Around here, you can get similar sounds from
colonies of barnacles. I'm sure that there are lots of species that
make similar noise by direct percussive technique or by making or
manipulating gas bubbles.
I have 10 meter
> cables with my H2a's, do you think I would benefit having longer
> cables, to better avoid surface noise?
If you're working our of a kayak, a longer cable might be cumbersome.
It can certainly distance the hydrophone from boat and surface noise.
And if I am correct about the cable strum while being adrift (or holding
your position in a current), the longer cable will lower that frequency,
which will be filtered more effectively by both the natural cutoff of
the hydrophone, preamp, recorder and by any rumble filter that you
engage. I think that, just as with other forms of nature recording, you
count on luck to present you with the right conditions and pick up
tricks with experience to help manage the times when you're not so lucky.
>
> Aloha, David
>
>
Aloha, Robb
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