The most common and lowest form of scrambling is called Voice Inversion.
It sounds like a squawking noise when listened to over a non-coded
receiver.
From there, encription goes digital. Actually changing voice sounds to
digital 0's and 1's which is decoded on the other end. This is the
highest form and can use many different "keys" to scramble the voice.
The voice inversion is usually enough to keep the casual listener from
understanding voice messages, but is prone to decoding due to it's
rather uncomplicated form.

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