> I need an inexpensive way to record and display
> (decibel v frequency) ultrasonic frequencies between 20kHz and
> 50kHz.
Michael,
Inexpensive, no. Any peripherals recording digitally at 44.1 or 48 cut
off at below half of those frequencies to avoid aliasing. Een 96Ks/s
sample rate is too slow. I do bat conservation work which involves
frequenies up to 110KHz. There are three methods of doing this with a
bat detector which makes bat frequencies audible.
1) heterodyne which shifts down all frequencies by a given amount, say
45KHz lower, but this only covers a range of about 8KHz.
2) frequency division which divides the frequency by (typically) 10
3) time expansion which records a second or two and then plays it back
at 1/8 or 1/10 or 1/16 speed. These have three zeroes on the price
tag.
You can get PCMCIA cards which digitise ultrasound but they also have
three zeroes. See if you can find some local bat enthusiasts who may
be able to help.
Alternatively you can simulate the sounds by generating similar sounds
at audible frequencies and displaying them using Audacity or another
sound editing program as power spectrums and audiograms, and alter the
scaling on the displays.
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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