Thanks Walt, Lang, Bernie, Dan for your responses. I'm ordering
another hydrophone and will go out and play around with it.
I'm passing along some responses gleaned from the Cetacean Research
email list. Joe Olsen suggests ~70 cm spacing for underwater stereo
recording.
from Cetacean Research email list:
-----------------------------------------------------
David,
Large numbers of snapping shrimp can be found in water
depths over 100 meters but tend to concentrate in
areas of high food content. This can be harbors, reefs
(fish, shark, turtle droppings) and in open water with
marine mammal droppings etc.
Snapping shrimp produce impulse sounds with a band
width of about 800 hz to over 100 khz and intensities
of 190db (ref. 1 microPa). The freq. of highest energy
is between 1 khz and 5 khz depending on where the
animal is doing the snapping.
I have made several stereo hydrophone recordings and
know of a researcher that placed four hydrophones in a
fixture with a four channel headphone system that
enabled him to get very accurate relative bearings to
whale pods.
The velocity of sound in seawater is about 1500 meters
per second, so knowing the distance between your two
hydrophones and the arrival time difference between
them, you can calculate the bearing, (+) (-) 180 deg.
Cheers,
Doug
__________________________________________________
From: Cetacean Research Technology
Date: Fri Nov 8, 2002 9:19am
Subject: Stereo hydrophones </group/CetaceanAcoustics/message/20?
expand=1>
I've built stereo hydrophone systems for researchers in Hawaii and the
Pacific Northwest. Separating two hydrophones by ~70cm works very
well for
reproducing the sound field while listening with headphones. It's
easy to
resolve the 180 degree ambiguity by turning the hydrophone fixture
while
listening. Information on the system will eventually be published in
paper
by Dr. John Potter and Dr. Adam Pack.
=======================
Joseph R. Olson
Cetacean Research Technology
PO Box 70186
Seattle, WA 98107
David,
You'll be hard pressed to eliminate snapping shrimp broadband sounds
from
your recordings. Short of spending $20k on Pro Tools, you might want
to
invest in Sound Forge. They make a pop and lick removal tool that I'm
guessing is much better than Cool Edit's.
Good luck,
Joe
=======================
Joseph R. Olson
Cetacean Research Technology
PO Box 70186
Seattle, WA 98107
-------------------------------------
--- In Walter Knapp <> wrote:
> David Kuhn wrote:
> > Hello listeners,
> > I've been recording Cetacean sounds when the opportunity arises.
> > In Hawaiian waters are Humpback, False Killer, Pilot, Melon-head,
and
> > Sperm whales, and Spinner, Bottlenose, Rough-toothed, Spotted,
and
> > Striped Dolphins, and more. I get some beautiful sounds and want
to
> > get more, but so far snapping shrimp dominate my recordings. I
use
> > Cool Edit Pro's "click and pop removal" feature seems overpowered
> > (detecting upwards of several hundred clicks per second!) and not
> > able to clean them up adequately. I read that snappers are in
depths
> > up to 30 m.(Can anyone confirm that info?), so I'm heading for
deep
> > water, but would like to salvage what I've got.
>
> When I lived in Hawaii, I spent large amounts of time out in the
water.
> The snapping shrimp were more common in the lagoon than outside the
> reef, but were both places. I dove well over 100' at some offshore
> islands that dropped straight down underwater, and they were there
too.
> And underwater their high energy snap would travel well.
>
> Have you checked if they are confined to frequencies you can
filter
> out? Check a sonogram and see. Certainly if you filtered all
frequencies
> except the call ones you wanted that should tone them down at least.
>
> > Another question: Most of my in-the-air recordings are stereo. Is
> > hydrophone stereo feasible, using mic's at either end of a 60'
boat?
>
> Speed of sound is faster in water, and the water surface is a
reflector.
> If the boat is in deep water it might work. Work like you are using
> spaced omni's but much farther apart. Definitely try each end of
the
> boat first.
>
> And let us know how you do.
>
> Walt
>
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