On Sun, 2010-05-09 at 13:20 -0500, Rob Danielson wrote:
> Is your goal to document the space with the bats as best as you can?
That was my original intention, following one from some informal
recording done using the recorder internal mics on the previous visit,
when we had no idea what to expect in the cave, e.g.:
http://soundcloud.com/user2340027/tmn-young-bat-vocalizing-2nd-cave-ear-cave-taman-negara-april-2010
where there is a background of bat wing beats, a young bat regularly
clicking near to the microphone, and occasional audible vocalizations
from other bats. However on the second visit it had been raining
heavily, there was more water in the cave and I failed to find the route
to the second chamber where the majority of the bats are.
There was though a continuous stream of bats flying through the outer
chamber to and from the second chamber, via a low passage just above the
water level. I really liked the sound of their wingbeats, and decided
to try and record that, even though I thought that the sound level might
really be too low for the equipment (it sounded possible in monitoring
though, so gave it a go).
> If so, I think it has more promise than you suggest. Do you know what
> those regular-spaced, 10-12 second long 5800K Hz tones are?
That would be a cicada on the outside of the cave. I was really
surprised to hear it at the time, but those things can be _really_ loud.
> I assume some bat passes are so much closer/louder that they need to
> be tamed before you can raise the playback level to hear softer
> sounds in the distance with the acoustics of the cave. It might be
> possible to address these transient peaks, adjust overall tonal
> balance and stereo imaging in one step and avoid multiple steps and
> normalization. If you'd like to post a 2 minute clip of the original
> as a flac file, we can give it a look/listen.
I would really be interested in better ways to deal with this issue. A
number of the recordings made on the trip have needed similar treatment
to get the quieter sounds up to a more practical level (aiming at
ordinary domestic speakers as well as good quality headphones), though
none needed as much post-processing as this recording.
I did have a go using a compressor, but don't really know what I am
doing with adjusting the parameters, and did not particularly like the
early results.
A 2 minute flac sample of the original recording can be downloaded from
here:
http://soundcloud.com/user2340027/1064-section-3-to-5-mins
> As for your gear/array approach to the setting, an X-Y mic is not a
> bad choice for a smaller space like this one.
That is helpful to know.
> Mic placement can be
> critical-- best to get away from the walls/ceiling/floor so the
> reflections are balanced and chances of phasing are lessened.
Thanks - did not know that. In this particular place there were not
many options. The flight path went close to a horizontal ledge about
waist height when I was standing on the cave floor, with the cave roof
about a metre or so above it, at an angle, and that was where I placed
the mic, with the centre-line parallel to, and right in, the general
flight path. Another time I would try with the tripod raised fully up
from the cave floor, with the centre-line at right-angles to the flight
path (could have tried that at the time, but it is odd how those
temperatures seem to reduce your brain capacity).
> A quieter mic might prove beneficial to focus on HF communications
> after things settled down. ... As-is, the commotion of the wing
> fluttering should be robust enough to get around an annoying amount
> of self-noise.
The mic was as close to the bats as possible. I'm thinking that a more
sensitive setup with lower self noise would have been more appropriate
for this particular task. Also wondering if just adding some
amplification between the microphone and the recorder, e.g.:
http://www.felmicamps.co.uk/products/felbattpreamp.html
would have made a big difference here? The AT 8022/Marantz PMD 620
combination produces reasonable results with more "robust" sound levels,
but with quieter sound sources the recording levels are lower than I
would like.
I much appreciate all the help.
Richard
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