I'm sorry to say that the option described by Raimund is not an emulation o=
f
the frequency division principle, is only a resampling without the required
low pass filtering and thus the resampling produces aliased components whos=
e
only merit is to made audible, but highly distorted, the components above
the Nyquist frequency of the resampling. This type of resampling is present
in the SeaPro software since 20 years ago; in the SeaWave program is just
hidden in a setting panel not available in the free version. Aliasing is on=
e
of the most basic topics in any introduction to digital signal processing.
A real frequency division system is based on a zero crossing algorithm that
produces a sine cycle every n cycles in the original signal; thus it
produces a synthetic signal whose amplitude is modulated by the amplitude o=
f
the original signal.
See http://www.unipv.it/cibra/edu_equipment_uk.html#batde
This frequency division procedure was implemented very well in a bat
detector produced by UltraSound Advice (model S25) in the '80. I used the
same principle to produce "images" of the spectral features of signals in
real-time in the same years, when the available computing power was not
enough to do fft computations in real time.
I would also recall the implementation of automatic frequency tracking, son=
g
parsing and song description used for publishing a paper in 1987 on the son=
g
of Cettia cetti. I see that something similar has been implemented in
Avisoft many years later...... mmmhhh strange....
all the best,
Gianni
2011/4/9 Raimund <>
>
>
> > I'll also be doing comparisons, to my current (Frequency division &
> Heterodyne) detectors.
>
> Hi Al,
>
> You might also try the free Avisoft-SASLab Lite software (
> http://www.avisoft.com/setup3.exe, http://www.avisoft.com/SASLabPro.pdf).
>
> There is an interesting feature in it that might help to become familiar
> with the differences between time expansion and frequency division bat
> detector technology: The menu 'File'/'Specials'/'Frequency Division Bat
> Detector Emulation' can convert high sample rate recordings (such as thos=
e
> made with a USB ultrasound microphone) to a waveform that corresponds to =
the
> output signal that you would hear if you recorded the bat by using a
> frequency division bat detector.
>
> Use the Command 'File'/'Playback setting...' to play your bat recording a=
t
> lower speeds (option 'other sample rate.'). You could also try the
> undersampling option (undersampl:) that performs a real-time broad-band
> conversion. This is probably the same mechanism that Gianni is going to
> implement now.
>
> Note that I (probably first) introduced this principle to bat detector
> technology in 1993 (implemented in the Laar Bridge Box time expansion
> detectors). It is now also available in the (more expensive) UltraSoundGa=
te
> USB microphones supported both by hardware and software. The hardware
> implementation has the advantage that there is virtually no delay between
> the occurrence of the ultrasounds and the converted output signal (just l=
ike
> in a conventional bat detector). This can be very important as the delay
> caused by a software solution can be annoying.
>
> Regards
>
>
>
--
Centro Interdisciplinare di Bioacustica e Ricerche Ambientali
Universit=E0 degli Studi di Pavia
Via Taramelli 24, 27100 Pavia
http://www.unipv.it/cibra
http://mammiferimarini.unipv.it
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