What are the best ways to mask a
voice tone, like what they do during news shows on television sometimes? Is there a way that is not reversibile? I think that a simple modulation is not the best solution.
I think voice masking is basicly a (phase-)vocoder. it uses ans external sound source as sound and use the formants as modulator. So the voice it self isn't used. In this way the voice can't be reconstruced to the original one.
See: vocoder wikipedia