Hi, Sue -- I have not done much bioacoustics yet but am an electrical
engineer / conservation biologist with experience in automatic electronic
measurement.
If you can, as you say, live with discontinuous recording (sampling each
cricket for a period of time), it sounds to me like an "analog switch" or
"multiplexing" circuit is what you need. A multiplexer (or "MX" in the
jargon) switches rapidly among various possible inputs -- in this
instance, microphones, feeding one at a time to the recording device. The
recording stream would then have to be tagged with a channel
identification signal for each sampled time interval. Alternatively, if
the multiplexing sequence were cyclical (microphone 1 to 50 and then back
to 1), you might need only a quick burst of some arbitrary tone to
indicate the beginning of the cycle, and then count time to identify
subsequent inputs. For your needs I might suggest your MX could be 50 spst
analog switches such as are available 4 or more amplifiers in a chip,
dedicating each amplifer to a microphone. Each could be gated "on" in
sequence by a counter / multiplexer digital chip. (See, for instance,
Analog Devices,
http://www.analog.com/en/prod/0,2877,768%255F833%255FADG411,00.html)
Perhaps a better alternative to such periodic sampling would be "VOX" or
voice-operated sampling, where you sense audio from one microphone and
then immediately gate that microphone's amplifer to the recording medium
as long as the sound persists. In this instance the sample would have to
be accompanied by an identifying tag, perhaps a binary code or unique tone
following the sound. Some sort of "collision avoidance" circuit would be
needed to ensure only one microphone operates at a time. You might lose a
few milliseconds of recording at the start of each chirp.
If your interest is in the frequency range you indicate, a very
inexpensive microphone indeed should suffice for each cricket.
It may well be that more experienced researchers are aware of audio
multiplexers already built for this work.
- Dave
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David C. Kay
Conservation Biologist
http://www.antiochne.edu/es/conbio/
Antioch New England Graduate School
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