> I bought a "Discovery Kids Ultrasonic Detector" on eBay for about $40. It=
's a heterodyne detector, and is of course a toy compared to some, but it s=
eems to work ok. I suspect though, that a software solution would be better=
.
This kind of heterodyne functionality is available in the free Avisoft-SAS=
Lab Lite software (http://www.avisoft.com/downloads.htm). Just open the .wa=
v file and activate the option "enable heterodyned playback" from the menu =
"File"/"Heterodyned Playback mode...", where the center frequency and bandw=
idth can be adjusted. If you then play the file by clicking at the play but=
ton, you will hear the heterodyned signal just like on an analog heterodyne=
bat detector.
The same software also allows to down-shift portions of a waveform using F=
FT (command "Edit"/"Filter"/"Frequency Domain Transformation..." > "Frequen=
cy Shift").
The SASLab Pro version (which is unfortunately not free) would also allow =
re-synthesizing any whistle-like sounds using its Graphic Synthesizer tool,=
which allows modifying time and frequency scales independently.
Regards,
Raimund
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