Remilia's Theme on Bat Detector [HD]
A heterodyne bat detector lets you hear the difference (frequency-wise) between the sounds around it, and a set frequency. So, doesn't that mean you can make ultrasonic music and then use the detector to shift the frequencies down so that a human can hear it? It sure does! =D
That said, I didn't actually make the music - it's the final boss theme ("Septette for a Dead Princess") from Touhou 06 (Embodiment of Scarlet Devil), as ripped directly from the game (in MIDI format).
I modified BaWaMI, a MIDI software synth that I made, so that you can shift the frequency of all notes up by a linear amount. This is different to simple "pitch-shifting", which MULTIPLIES the frequencies by a set amount. That's why it sounds horribly out-of-tune when shifted - the frequency is made to range from something other than 0 Hz. When shifted by exactly the right amount, the detector is able to recreate the sound as ranging from 0 Hz again. Because the detector is designed to be accurate to a few KHz rather than a few dozen Hz, its internal oscillator tends to "drift" a bit, so I have to keep adjusting the tuning on my program to compensate.
This bat detector is the Ciel-electronique CDB 301 (the newest revision includes a built-in speaker).
(Yes, bat videos will come some time, but they might have to wait until next summer, as little Remi is going into hibernation now x3)
BaWaMI is released now! See lots of info and download it here:
http://somethingunreal.homeip.net/blog?page_id=84#bawami