Wow! Amazing stuff! Great info for my notebook!
Cool...
Gentlemen, get your blackboards & chalk ready : )
Thanks!
-Al
--- In Gianni Pavan <> wrote:
>
> I'm sorry to say that the option described by Raimund is not an emulation=
of
> the frequency division principle, is only a resampling without the requir=
ed
> low pass filtering and thus the resampling produces aliased components wh=
ose
> only merit is to made audible, but highly distorted, the components above
> the Nyquist frequency of the resampling. This type of resampling is prese=
nt
> 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 =
one
> of the most basic topics in any introduction to digital signal processing=
.
>
> A real frequency division system is based on a zero crossing algorithm th=
at
> produces a sine cycle every n cycles in the original signal; thus it
> produces a synthetic signal whose amplitude is modulated by the amplitude=
of
> 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, s=
ong
> parsing and song description used for publishing a paper in 1987 on the s=
ong
> 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 familia=
r
> > 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 th=
ose
> > made with a USB ultrasound microphone) to a waveform that corresponds t=
o 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=
at
> > 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) UltraSound=
Gate
> > USB microphones supported both by hardware and software. The hardware
> > implementation has the advantage that there is virtually no delay betwe=
en
> > the occurrence of the ultrasounds and the converted output signal (just=
like
> > in a conventional bat detector). This can be very important as the dela=
y
> > 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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