> From: Steve Pelikan <>
> >
> > Many of the small AD converters will now do 96KHz, enough to record
> sounds
> > up through 48KHz.
> >
> > And I've read there there's a couple that do 193, which is enough for
> > recording any bat I've every heard about!
>
> It is worth remembering that a AD converter is not by itself a field
> recorder. It's a hardware component, one of many parts needed. The
> question on recorders is about something you might toss on your shoulder=
> and go out in the field and record with.
>
> The problems of high frequency recording are less in the AD and a whole
> lot more in other parts.
>
> Right now, to do this stuff at high quality in the field tends to come
> down to packing a computer out there. A very cumbersome solution.
>
> Walt
>
One should note, that 192 kHz recording equipment might not be suited for
recording any sorts of bat echolocation calls. Usually, it is not possible
to exploit the theoretically possible maximum signal bandwidth of 96 kHz if
there are any signal components above the 96 kHz limit (the practical limit
is about 80 kHz). The problem is that the integrated anti-aliasing filters
do not fully reject sound components slightly above the Nyquist frequency
(half of the sample rate). Such high-pitched sound components (harmonics of
bat calls may go up to 200 kHz) would be folded down to lower frequencies
below 96 kHz. However, most audio microphones have much lower bandwidths
(they act as an additional anti-aliasing filter), which would prevent such
potential aliasing problems.
There are special solutions for recording bat calls that use special
ultrasound microphones and higher sample rates (up to 500 kHz). One of thes=
e
is the UltraSoundGate system. Even if it requires a computer, it is possibl=
e
to prepare a relatively compact unit by using a compact mini notebook PC:
http://www.ultrasoundgate.com/jvcopen.jpg
http://www.ultrasoundgate.com/jvcclosed.jpg
Regards,
Raimund
Avisoft Bioacoustics
http://www.ultrasoundgate.com
--
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________________________________________________________________________
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"Microphones are not ears,
Loudspeakers are not birds,
A listening room is not nature."
Klas Strandberg
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