Another crazy idea I had which turned into a VST plugin is a spectral mirror. I’m not really sure if that is an appropriate name for it. What it does is that it takes a band of frequencies (for example frequencies 0 Hz thru 4 Hz) and flips it around so that a high frequency becomes a low one and a low becomes a high frequency. How it does this is based on modulation; it modulates the band of frequencies thru the zero frequency aided with steep filtering to remove unwanted sidebands.
The result sounds unnatural because the frequencies aren’t harmonic anymore. The effect is best on human speech, since it really tricks your perception of it. I guess it’s due to the time domain having roughly the same characteristics but the frequencies aren’t perceived anymore as speech. In other words it almost sounds like speech in some weird way but is still unintelligible.
Here is an example. It’s a talk on Kurt Gödel by Rebecca Goldstein (http://www.edge.org/3rd_culture/goldstein05/goldstein05_index.html)
The original talk:
The talk thru the mirror vst:
Here is a link to the win32 dynamic link library: