# How to make ultrasound audible?

Because of interesting spectral phenomena, I would like to shift the >20kHz content of my audio recordings to audible frequencies, so that I can listen to it. I tried the Audacity pitch correction feature, but didn't succeed. Any help much appreciated.

• What do you mean by "didn't succeed"? Did it crash, nothing was audible or too much low-frequency noise?
– jojek
Sep 7 '20 at 8:50
• Long time since I did this by just changing the sample rate of WAV file (HEX editor needed). Sep 7 '20 at 8:50
• How did you collect these audio recordings? All audio equipment I've touched, even if it samples at 96 kHz, has analog anti-aliasing filters that cut off somewhere below 20 kHz. Sep 7 '20 at 8:54
• @MarcusMüller: In my case hydrogenaud.io/index.php?topic=106205.0 Sep 7 '20 at 9:07
• @W.H.G. I am more of a console guy. You can try to use sox with pitch effect. Something like: sox in.wav -r44.1k out.wav pitch -2400, which will shift the signal down by 24 semi-tones (2 octaves). So 40 kHz becomes 10 kHz, etc. Finally, it will save the output to 44.1k audio file. You might want to do some high-pass (or even band-pass) filtering on the output.
– jojek
Sep 7 '20 at 11:53

sox in.wav -r44.1k out.wav