This type of audio encryption has a pretty good strategy. Most people who heard sounds like this on their radio would just give their radio a couple of smacks thinking it was a loose connection or think it was some kind of interference or something and move on.
You'd need a shortwave radio, which most people don't have. Also, the signal is being transmitted on several frequencies at the same time. You'd have to be able to merge all the sounds in the right way to get intelligible conversation.
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