Most of us know about voice scrambler that can be used across almost any kind of voice based communication technology.
Extremely flexible approach: works everything
Extreme performance: very low latency
Extremely weak: Scrambling cannot be considered secure.
Only encryption can be considered secure under the Kerckoff’s principle .
So please don’t even consider any kind of analog scrambler if you need real security.
Read deeply the paper Implementation of a real-time voice encryption system” by Markus Brandau, especially the cryptoanalysis paragraph.