At 10:43 AM +0100 5/10/10, Richard Folwell wrote:
> 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>http://soundcloud.com/user2340027/tmn-young-bat-vocalizing-2nd-cave-ear-cave-taman-negara-april-2010
>
><snip>...
>
>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.
Hi Richard--
See my comment about recorder input noise below.
>A 2 minute flac sample of the original recording can be downloaded from
>here:
>
><http://soundcloud.com/user2340027/1064-section-3-to-5-mins>http://soundcloud.com/user2340027/1064-section-3-to-5-mins
Got it. I'll see what I can so with it as a learning opportunity for
both of us. :-)
>
> > 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).
At first listen, there could be considerable resonance as result of
some standing waves from the enclosure. Its a challenge to hear this
phenomenon in the field. Fully-enclosed headphones and moving the
rig around as you monitor can help you detect it. Its usually not
possible to escape them entirely but you can often find more or less
pleasing blending of the tones.
> > 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>http://www.felmicamps.co.uk/products/felbattpreamp.html
I don't think this would improve noise performance in this case.
>
>would have made a big difference here? The AT 8022/Marantz PMD 620
>combination produces reasonable results with more "robust" sound levels,
Your gain in th bat recording looks workable. I'd record in 24 bit
mode when I expect lots of level variations like this. The AT 8022
has 12.5 mV/Pa sensitivity which is considerably lower, if the 620
has limited mic pre gain, you may indeed have some challenges in this
dept in quiet settings.
Glad I asked about the recorder. Raimund measured the PMD 620's input
noise around -112dBu (A weighted)
http://www.avisoft.com/recordertests.htm which, unfortunately, will
introduce mic preamp noise when used with quieter mics. I think I
might hear some noise from the PMD 620's mic pre in the bat
recording. -112dBu is workable for robust sound sources but its iffy
for softer ones like this.
I noticed at the Recordists Campout 10 days ago that many of the
recordists had a Fostex FR2-LE in their bags. Lots of AT3032's and
AT4022's too. Seems like a hard performance/value combination to
beat. Lots of array options with omni mics too. Rob D.
>but with quieter sound sources the recording levels are lower than I
>would like.
>
>I much appreciate all the help.
>
>Richard
--
|