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The catalyzer is a project to convert audio from the ultrasonic frequencies down to the audible range in real time. The theory is to capture data at 200khz (requires a special mic and pre-amp); FFT the data; divide all frequencies by 4 and re-bin them; and finally inverse-FFT (and normalize) the result.

cmd: arecord --device=hw:CARD=X20,DEV=0 -t raw -f S32_LE -c 2 -r 192000 | ./catalyze | aplay --device=hw:CARD=X20,DEV=0 -f S32_LE -c 2 -r 192000

To build: 1) install fftw3 (in debian/ubuntu: apt-get install libfftw3-dev 2) cd src; make 3) be happy