How would I spectrally rotate/invert an audio signal (Matlab or Python)? So I have a 4.5 minute wav audio clip. I want to spectrally rotate the frequencies such that the spatio-temporal characteristics of natural speech are retained, while having the new audio be unintelligible. Any tips? I found https://ccrma.stanford.edu/~jos/sasp/Spectral_Rotation_Real_Signals.html, but I'm not getting anywhere with it.
$$ y[n] = (-1)^n \cdot x[n] $$
This will flip the spectrum in linear frequency. Easy to do, easy to recover.