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REVEIL 2021: Listening to Bats, 1-2 May

A Little Brown Bat at Arcadia, in a binaural decode from an ambisonic recording.
A Big Brown Bat, recorded in my back yard using an A/B stereo array.

Last year, as part of Soundcamp’s REVEIL festival, I had the great pleasure of moderating a discussion about the sound world of bats, and how listening to bats can help us better understand and protect them. This coming Saturday 1 May I’m looking forward to revisiting the topic as part of REVEIL 2021. Joining our discussion as last time will be researcher Erin Ruggiano, and this time Erin and I will be able to meet in person at the Massachusetts Audubon Arcadia Wildlife Preserve to hunt for bat sounds. Using sensors that can modulate a bat’s calls into the human hearing range, we hope to give REVEIL’s global audience an audible glimpse of the Big Brown Bat (Eptesicus fuscus), the Eastern Red (Lasiurus borealis), and with luck, the endangered Little Brown Bat (Myotis lucifugus). The discussion starts 7:30 PM Massachusetts time, UTC-4. For our UK and Europe friends that’s the wee small hours!

On a recent survey at Arcadia, I was able to pick up this recording of a Little Brown Bat using my Sennheiser ambisonic microphone. I wasn’t sure I’d get anything on that mic, which is only rated up to 20 kHz, but I was able to get some decent (if a bit noisy) recordings of this bat hunting at around 50 kHz.

Last night I set up a pair of LOM Uši Pro mics in an AB array in my backyard, and got some really clear recordings of a Large Brown Bat.

In both cases I recorded to a Sound Devices MixPre6 operating at 192 kHz sampling rate. I decoded the ambisonic recording using the Harpex-X plugin in Reaper, and did the pitch-shifting and filtering in Izotope RX. I generally prefer to pitch-shift bat recordings by changing the sampling rate and simply reading the file more slowly; that preserves the original data and doesn’t introduce artifacts. Also, it gives an interesting insight into how the bat might be listening, by letting you hear the reverb tails as the calls bounce off of objects (and, ideally, moths).

I plan to spend more time this spring testing different mic arrays for bats; my intention is to get bat recordings that are not only as clean as possible, but can also give us spatial information about the bats movements. I suspect that some of the quick echos we get from these recordings are the bat’s calls bouncing off of buildings.

Bats already had an undeserved bad reputation before the coronavirus pandemic, but since then, it’s been the easy – but unproven – assumption that humans got SARS-CoV-2 from bats. In fact, bat rescuers take precautious to avoid giving the virus *to* bats, though it’s not known whether bats can become ill from the virus.

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Wood Frogs in a vernal pool at Audubon Arcadia, Easthampton MA

Wood frogs in a vernal pool

Wood frogs are starting to wake up and call to each other in vernal pools around here. I visited a large pool just behind the visitor’s center at Mass Audubon’s Arcadia Wildlife Refuge. I got some great recordings of frogs there exactly a year ago, working with Maine-based sound artist Steve Norton. I’m pretty sure that’s the last time I did anything in person with a friend with no mask and no distancing.

If you listen with headphones, be aware that some of these frogs get very loud. There’s one in the left channel who sounds like he’s croaking right into the mic – which is possible, since I recorded with a pair of LOM Uši Pro omnis dangled maybe an inch above the surface of the water. In between this frog’s sharp, high barks, you can hear a quiet sort of moan, perhaps the air he’s building up to make the next loud call. The land edge of the pool is just under the left mic, so he may be sitting on that, making his calls closer, and perhaps even louder for bouncing off of both the surface of the water and the underside of the wooden walkway.

After this flurry, the frog calls died down more suddenly than they started. The clip ends with a rustling sound, perhaps our soloist hopping away.

In the photo you can see two neon-red hairy puffs – those are the Uši Pro in a pair of the windshields we make here at EIS HQ.

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Window pass-through for microphone cables

I cut down a pool noodle (a long foam floatation toy for swimming pools) to serve as a window pass-through for the birdfeeder microphones. The foam cuts easily with a pocket knife and does a decent job of keeping out the last cold drafts of late winter, though I still take it out at night. A 2-inch deep slice at the halfway point is enough to pass the microphone cable through without compromising the window seal.

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Maple sap sounds on our live stream

EDIT 3/17/21: It’s been cold again here and the sap has temporarily slowed/stopped. Also, we’ve been noticing more bird activity in the trees a little bit behind this tree. So we’ve moved the streambox back there for the time being. The best time to listen is probably early in the morning our time, EST in the US (recently UTC-4 instead of UTC-5, thanks to the antiquated foolishness called Daylight Savings Time).

The sounds of running maple sap are now on our live stream on the Locus Sonus soundmap.

The sap is running in New England and beyond, and is harvested through the late winter/spring to be boiled down into the gold of the north, maple syrup. You’ll also hear locals like black-capped chickadee, tufted titmouse, and downy woodpecker.

We connected a pair of LOM Uši Pro and stuck them under the lid with magnetic clips, then ran them into our SoundcampStreambox.(More information on the Streambox, including how you can make one yourself, is here.)

Video by orangecookie
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Lyman Loop, Westhampton MA

Ambisonic recording decoded to Blumlein stereo

A windy day in the Lynes Woods Wildlife Sanctuary, on the Lyman loop. Nearly still under the trees, with no other people and no virtually wildlife except for some distant crows, the sky above the trees was on the move. I love the full sound of the rush of wind high up in the sky, and the Sennheiser Ambeo microphone seems to enjoy it too. Here I have decoded the recording in Bluemlein stereo; I often find Blumlein gives a rich rendering of the sense of space, with detail and room.