1. A method of rendering an intelligible analog electrical speech signal unintelligible but recognizable as representing speech, characterized by the steps of subjecting the speech signal to a first prescribed type of electrical signal distortion to produce a distorted signal and then subjecting the distorted signal to a second prescribed type of electrical signal distortion, wherein one of the first and second prescribed types of distortion consists of generating samples of the speech signal or distorted signal, with each sample having a duration within the range of 100 milliseconds to 1 second and having a ratio of sample-on time to the sum of sample-off time plus sample-on time within the range of 20% to 67%.