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From: ajpierce@ulah.med.unc.edu (Andrew Pierce)
Newsgroups: sci.bio
Subject: Re: The internal buzz
Keywords: bats
Message-ID: <2580@beguine.UUCP>
Date: 12 Feb 91 22:53:27 GMT
References: <91041.230852IO80214@MAINE.BITNET>
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Reply-To: ajpierce@uncmed.med.unc.edu (Andrew Pierce)
Organization: UNC-CH School of Medicine
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In article <91041.230852IO80214@MAINE.BITNET> IO80214@MAINE.BITNET (Jake) writes:
>
>      Just on a curious note; what causes the high pitched
>sound that one hears when all else is quiet?  Also, is there

   I don't know what causes the sound you here but I hear it too.  I can
also tell if a TV is on in the next room, even with the volume muted off,
by the high pitched humming it makes.  It is interesting that bats with
their echo-location sensing are apparently able to hear up to 150 kHz vs
30 kHz max for humans.  At 150 kHz is it almost getting to the point where
the bats can hear thermal noise, ie. the motion of the molecules in air.
     -Andy