A time and frequency-domain speech scrambler

A combined time- and frequency-domain speech scrambler that is designed to reduce residual intelligibility to zero by removing all clues for auditory perception from the scrambled speech is described. The recovered speech quality is good. Although implemented using an FFT (fast Fourier transform) algorithm, which is a batch process, the method does not require frame synchronization, and synchronization requirements for key changes are relatively lax. The proposal has been tested by simulation using, among other channels, an HF radio link simulator. The results confirm the performance of the scrambler, showing that it is robust enough for use on poor-quality HF channels