> I've been pondering about buying a bat detector to record bats and other =
ultrasonic sounds. budget is 200=E2=82=AC max. to record, I'd connect it to=
my sony pcm10, So I'd like one with a decent line out. Unfortunately, I do=
n't have a tablet, so the ultramic is out of the picture. I know the theor=
etical difference between heterodyne, frequency division and time expansion=
, but I don't know how they sound differently. Time expansion will be too e=
xpensive Any insights?
In the UK the "standard issue" detector is the Batbox Duet:
http://www.batbox.com/Downloads/Batbox-duet-instructions.pdf
This has two outputs on a 3.5mm jack, heterodyne and frequency division,
which can be recorded on any audio recorder. It also has a loudspeaker on
the heterodyne output.
In use, you adjust the HD frequency to the bat calling frequencies, and the=
three types of sounds you are likely to hear are frequency modulation (FM)=
clicks, constant frequency (CF) peeps or a "hockey stick" call which ends i=
n
a plop at the end CF part. All these frequencies give clues to the species.=
The FD part doesn't have an adjustment but generates a 1/10th frequency
signal by waveform counting. The Duet also nearly restores the original
amplitude unlike some othe makes of FD detector so you get an indication of=
bat distance.
There are other makes but some don't register the amplitude on the frequenc=
y
division side. Instead they have a threshold setting which mutes out noise=
and weak calls.
The recordings can be analysed using Audacity or other sound editors with a=
spectrogram and power spectrum analyser or custom bat programs. Multiplying=
by 10 gives the original bat call frequencies but the waveform is not
preserved and you lose 9/10th of the definition, but getting all that can
add another zero to the price of a detector.
See also:
http://en.wikipedia.org/wiki/Bat_detector
http://en.wikipedia.org/wiki/Bat_species_identification
David Brinicombe
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