> Inaudible ultrasonics contribute to intermodulation distortion in the audible range. Systems not designed to reproduce ultrasonics typically have much higher levels of distortion above 20 kHz, further contributing to intermodulation. Widening a design's frequency range to account for ultrasonics requires compromises that decrease noise and distortion performance within the audible spectrum. Either way, unneccessary reproduction of ultrasonic content diminishes performance.
- Christopher "Monty" Montgomery, the original author of the Ogg codec, founder of the Xiph.org Foundation, a real audio engineer.
It was to scare away the stone marter family that had made themselves a home under my parents' roof tiles. They are a protected animal where I live, so you can't just do anything to get rid of them. But they also tend to chew on cables in your car (they really do), making them dangerous. Also make a LOT of noise when they go hunting at night.
Looking up various ways to get rid of these animals (apparently they also really dislike the smell of toilet fresheners, which you can place under your car hood or something), I found an ultrasound device but it was kinda expensive for single use.
So I generated a bunch of high frequency tones, to make it extra annoying I had it do random(10,20) seconds of beep, then random(10,20) seconds of silence.
I burned this to a CD, made three tracks at 15kHz, 17kHz and 19kHz. I didn't go higher because I had no way to find out if the speakers would be able to reproduce that tone :) I could clearly hear 15k, and my parents a little. I could nearly hear 17k, and my parents swore they heard nothing. Neither of us could hear the 19k, even at the loudest volume.
Since I don't live there, we decided to put the 17k track on repeat, at max volume, because at least we knew it made a sound (that I could barely hear). The CD player was placed next to an open window close to the nest.
That very night, the stone marter family got up and left. We assumed they probably just moved a few houses over, or something. However ...
Just to be sure they wouldn't return, my parents left the CD player on repeat for an entire week. After that week when my dad turned off the CD, five minutes later, he walked into the garden ...
"Hey, the birds are back!"
(... and to think there's a popular route close to their house for people walking their dogs ...)
So yeah, that definitely worked. It's just not very specific :-P
Not annoy, but learn more about them. The original idea of investigating ultrasound environment came to me when I was taking care of some rats for a few weeks for a friend; I read a short book on them, from which I've learned that they communicate with ultrasound, which made me want to "listen in" on that communication, and perhaps replay some of it.
FWIW, I have a cat myself, and I'm not the kind of person to annoy animals on purpose.
I'm not very good with electronics, but someone who is showed me this cool device they built themselves. It was something like a "frequency-lowerer" (NO idea how that works, I know DSP but not the analog stuff) and the intended use was to be able to hear the screeches of bats. One way to test it was to jingle a bunch of keys in front of its mic, the metal clanging has a lot of ultrasound.
I dunno how hard they are to build (that guy was pretty skilled), but I think you can also just buy these devices ready made. Probably called "bat detectors" or something.
- Christopher "Monty" Montgomery, the original author of the Ogg codec, founder of the Xiph.org Foundation, a real audio engineer.
https://people.xiph.org/~xiphmont/demo/neil-young.html