1. A method of distorting a speech signal, having frequency bands, by at least one of the operations of rearranging and reversing frequency bands in said signal, said method comprising: dividing the speech signal into a plurality of sub-bands by filtering; individually sampling each of the sub-bands at a sampling frequency which is the same for each sub-band and which is at least double that of the bandwidth of the sub-bands for providing a plurality of first spectra of samples (FIG. 3b), each with periodic repetition of the respective sub-band; reversing the polarity of alternate of said samples to provide a plurality of second spectra of samples (FIG. 3c), each with periodic repetition of the respective sub-band in a frequency reversed form; filtering out from said first spectra or from said second spectra a sub-band corresponding to the original sub-band displaced with a desired number of sub-bands in dependence on a control signal; and adding all the obtained sub-bands for transmission of the distorted signal.