Rob Danielson, you wrote:
>Thanks for the careful proposal Dan. It would be great for many folks
>to be able to participate.
This is in conjunction with a pilot program for attended monitoring
at Muir Woods National Monument. A corps of volunteers is using PDAs
to do monitoring at five locations at four times of day and three
day-classes (weekday, Saturday, Sunday). Locations vary from the busy
park entrance through a trail off the beaten track. It's possible to
do all five locations in one time slot in about two hours. The
program is up and running, and a significant database has been
compiled by about a dozen volunteers!
The Nature Sounds Society pledged to attempt to add some recording to
this program, by recordist volunteers making recordings while doing
the monitoring. So far we have two couple-teams and two individuals
contributing recordings.
>Could the procedure be simpler and still
>get the data that is most needed? I'd have to be really psych'd up
>for the strenuous calibration method you've outlined.
With today's great cheap gear, getting good recording documents is
within reach. The qualitative value of the data is there. It would be
even better if we could achieve SPL calibration, but that's a hell of
a challenge. Another idea is to build a calibrator that's a
transistor radio playing noise at a calibrated level with an antenna
"probe" to put the mic at a known distance.
The hope is to increase the scientific value, and the defensibility,
of amateur contributions to the parks soundscape inventory and
monitoring efforts.
>For example,
>if one knows the exact mics and recorder/recorder level used, a post
>test with the gear would probably determine the ambient levels with
>as much accuracy as the calibration test.
Yes, I used that technique for calibrating my recordings for the
visitor survey, another project at Muir Woods.
>With the larger part of the
>non-natural sound energy coming from a distance at under 50Hz,
>wouldn't it be very tough to set up relevant field calibration?
That's why I suggest that the recordist use a voice annoucement to
set a ballpark recording level. Works for me!
>For
>record level instruction, how about something like "...set at -5dB
>during a loud, distant event. If a louder event comes, re-adjust the
>record level for -5dB (or -10dB, but this is often not marked) and
>record for another 30 minutes"
Too vague and too variable. Of course the voice method is quite
variable, but it can give the recordist a place to start from sans
any other calibration method.
>Bit depth helps with the accuracy of
>the analysis tools I've used and some extra noise is not usually a
>concern. I've used the voice method you describe many times in the
>city, isn't the dynamic range in the woods too low for this method?
>(or is the pollution THAT serious!)
Recording with 65dB SPL peaking at -5dBFS (and averaging around
-15dBFS) brings the mic noise well above the floor of 16-bit
recording. For the last several years I've recorded a wide variety of
soundscapes with this level, which is what I get with 183s into a
Sharp MD at MIC L 17. I found I had to drop my level 6dB (MIC L 14)
to cover the crowded parts of the park. I can't recall any natural
sounds except thunder I've had to turn down for, and some wind
situations where the sound per se wasn't that loud but I wanted to
keep the wind noise in the mics below clipping.
>I agree that careful note
>taking is really important. Having assigned "15 minute" takes on many
>occasion, I'd specify at least a half hour. Rob D.
The "Soundscape" Palm software that the Park Service has developed
has revolutionized attended monitoring. It's here, and it works! It
solves the note taking problem, and has promise, with a little more
development, of becoming a standard way forannotating any soundscape
recording.
The session length was developed after experience with attended
logging. It's about as long as a volunteer can sit still. I've done
forty-minute hand-held takes, but I'm a fanatic!
-Dan Dugan
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