Thanks for the reply David. However, I don't think you understand my needs.
I don't need the ultrasonic frequencies to be audible. I just need to record
ultrasonic sounds between 20kHz and 50kHz and display them on a graph showing
frequency and decibel levels. I am doing this in the lab so I thought there
may be a USB microphone/computer software program I could use.
--- In "Avocet" <> wrote:
>
> > 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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