<br><br><div class="gmail_quote">On Wed, Sep 21, 2011 at 10:44 PM, Hans-Christoph Steiner <span dir="ltr"><<a href="mailto:hans@at.or.at">hans@at.or.at</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
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I'm trying to come up with a simple voice scrambling technique that<br>
leaves voices understandable, but makes them unrecognizable. A key part<br>
of this is to make it very hard to reverse the scrambling to make the<br>
voice more recognizable.<br>
<br>
I'm currently thinking that a ring modulator would work well for this,<br>
and it uses minimal CPU. Can anyone think of a way to reverse the ring<br>
modulation? I attached my quick sketch.</blockquote><div><br></div><div>That's a nice challenge. If I were CIA, I'd try to descramble like this: demodulate (division instead of multiplication) with a sine sweep while analyzing the spectrum. At the sweep frequency where the spectrum is a harmonic recipe: bingo, a human voice. Then you could demodulate that 0.1 second of sound with the found frequency. Not something to quickly do in a Pd patch though.</div>
<div><br></div><div>If your scrambler would modulate the modulation frequency continuously, with a noise signal, speech is still intelligible, but descrambling in the above described way would no longer be possible, as you can't find a harmonic recipe from a one sample fourier transform.</div>
<div><br></div><div>Katja</div></div>