Good work!
Just because a microphone is rated to work from 40-20,000 Hz doesn't mean t=
hat it stops being able to pick up sounds above that range. =A0It just roll=
s off. =A0If it's an omni it probably rolls off at 12 dB/octave and if it's=
a cardioid it probably rolls off a little slower. =A0You didn't say which =
type of capsule you were using on your C4s. That would imply that your C4s =
are down 12 dB or more by 40 kHz, but that doesn't stop them from picking u=
p sounds that are loud.
=A0Bat calls are pretty intense. =A0I should have started by saying that I =
know next to nothing about bats, but I do know that they use chirps to eval=
uate their surrounds. =A0So do radar and sonar transmitters. =A0It's an eff=
icient way to do measurements. =A0That's what I use to measure microphones!
On Saturday, June 7, 2014 10:29 AM, "'Chris Harrison' [=
naturerecordists]" <> wrote:
=A0
Hi all,
=A0
I am really trying to figure out if I am hearing what I=E2=80=99m hearing.
=A0
I was trying to record some insects in the desert mountains of western Texa=
s last month.=A0 I was using my Tascam DR-680 and a pair of inexpensive Stu=
dio Projects C4 microphones in a mic stand.=A0=A0 As a side note, they are =
decent microphones for the price and I have been pretty happy with them ove=
rall for the $350 per pair that I paid.=A0 They aren=E2=80=99t as quiet as =
an AT 4022 (microphone-data.com reports -13dB-A for the AT4022, -16dB-A for=
Studio Projects C4), but they are half the price, come with cardiod and om=
ni heads, and are quiet enough for entry level nature recording in my limit=
ed experience.=A0 But I digress.
=A0
While I was recording at a 48khz sampling rate, I noticed a bat swooping do=
wn around my microphone probably attracted to my vehicle parking lights.=A0=
=A0 So, just for fun, I started recording at 192Khz even though my micropho=
nes have a frequency response of 40Hz-20KHz.=A0 I didn=E2=80=99t expect to =
record anything other than crickets and a Common Poorwill or two.
=A0
However, when I pulled up the file in Audacity, I noticed a series of clear=
ly defined calls somewhere between 40Khz and 50Khz.=A0 Here=E2=80=99s a scr=
een shot of the 0.6 seconds of the spectrogram (I am just looking at the ri=
ght track for simplicity) =E2=80=93
=A0
http://www.pbase.com/sandboa/image/155987370
=A0
I then slowed it down to 10% of the original speed to hear what I was seein=
g and this was the result (sl! owing it down seems to make a lot of hiss th=
at isn=E2=80=99t audible in the original recording) =E2=80=93
=A0
https://soundcloud.com/sandboa/ultrasonic-bat-recording-from-non-ultrasonic=
-mic
=A0
My questions are:
=A0
Message: 1.
Subject: =A0 Are these bat echolocation calls?=A0 I could see the bat swooping
dow=
n over the area where the mics were standing.=A0 And it seems to accelerate=
rapidly around 8 seconds in =E2=80=93 maybe it found a bug?
=A0
Message: 2.
Subject: =A0 Is it normal for a microphone with a published frequency response
of =
40-20,000Hz to pick up sounds at 40,000+ Hz?
=A0
Thanks in advance.
=A0
Chris
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