I'm an electrical guy, so I know how to make a frequency converter electrically. Or by using software through resampling, etc. My mechanical understanding of the world is much more lacking. What I'm wondering is if there is a purely mechanical way of changing the frequency of a sound? Is it possible in theory or are there working devices that do this?
I'm not talking an ideal device, some smoothing / muddling of the frequencies would be fine. Just in general, say it was human voice - to roughly move the frequency down an octave from the original person's voice - or say, take a high frequency hum of a high speed metal fan blade and take the high frequency sound it creates and create a more pleasant, low frequency hum. In my mind, I'm thinking something like a resonating chamber except it actually changes the frequencies rather than just amplify them.
My first thought (probably stupid) is some sort of small, isolated gas inside a bladder inside a resonator? Like a bladder full of helium or sulfur hexafluoride? Second thought (also probably stupid), maybe a chamber full of wooden balls and/or tubes similar to a wind chime?
Just to be clear: I'm talking a device that would create sounds at a frequency or frequencies that completely did not exist in the original sound. Not something that would simply filter out certain frequencies and resonate others.