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ultrasonic bat recording with "non-ultrasonic" mics

Subject: ultrasonic bat recording with "non-ultrasonic" mics
From: "Chris Harrison" lamprophis1963
Date: Sat Jun 7, 2014 10:29 am ((PDT))
Hi all,

I am really trying to figure out if I am hearing what I'm hearing.

I was trying to record some insects in the desert mountains of western Texa=
last month.  I was using my Tascam DR-680 and a pair of inexpensive Studio
Projects C4 microphones in a mic stand.   As a side note, they are decent
microphones for the price and I have been pretty happy with them overall fo=
the $350 per pair that I paid.  They aren't as quiet as an AT 4022
( reports -13dB-A for the AT4022, -16dB-A for Studio
Projects C4), but they are half the price, come with cardiod and omni heads=
and are quiet enough for entry level nature recording in my limited
experience.  But I digress.

While I was recording at a 48khz sampling rate, I noticed a bat swooping
down around my microphone probably attracted to my vehicle parking lights.
So, just for fun, I started recording at 192Khz even though my microphones
have a frequency response of 40Hz-20KHz.  I didn't expect to record anythin=
other than crickets and a Common Poorwill or two.

However, when I pulled up the file in Audacity, I noticed a series of
clearly defined calls somewhere between 40Khz and 50Khz.  Here's a screen
shot of the 0.6 seconds of the spectrogram (I am just looking at the right
track for simplicity) -

I then slowed it down to 10% of the original speed to hear what I was seein=
and this was the result (slowing it down seems to make a lot of hiss that
isn't audible in the original recording) -

My questions are:

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