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Re: ultrasonic bat recording with "non-ultrasonic" mics

Subject: Re: ultrasonic bat recording with "non-ultrasonic" mics
From: madl74
Date: Sat Jun 7, 2014 3:41 pm ((PDT))
> 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 righ=
> track for simplicity) -


I see a bat "hockey stick" call of what would be a Pipistrelle bat (P,
nathusii?) in the UK. The call sweeps downwards with the FM element slowing=

down near the end. The defining frequency for this type of call is the end=

frequency which is 42/43 KHz on the audiogram.

Interestingly, there is also an echo after the call which may be from
foliage or the ground, and I'll leave it to you to calculate the echo

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


Apart from out-of-spec mic and preamp hiss, there will be quite a lot of U/=
HF noise out there, apart from the thermal noise of the air which rises at=

6dB per octave.

The sound is better than you get from many affordable bat detectors.

> 1.  Are these bat echolocation calls?

Yes, general scanning navigation calls.

> And it seems to accelerate rapidly around 8 seconds in

That's a "feeding buzz" homing in on a target insect. There is also a short=

pause after the feeding buzz which could indicate a capture and rapid gulp.=

> 2.  Is it normal for a microphone with a published frequency response of
> 40-20,000Hz to pick up sounds at 40,000+ Hz?

Yes, unless the manufacturer deliberately trims the HF response, which is
rare. They just donl't quote it in the spec as it can't be guaranteed +/- a=

few dB and would look bad on a response curve. Most bat detectors use audio=

type capsules.

David Brinicombe

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