Speech Encryption by Manipulations of LPC Parameters
M. R. Sambur, Nikil S. Jayant · Bell System Technical Journal · 1976
This paper discusses several manipulations of lpc (linear predictive coding) parameters for providing speech encryption. Specifically, the paper considers temporal rearrangement or scrambling of the lpc code sequence, as well as the alternative of perturbing individual samples in the sequence by means of pseudo-random additive or multiplicative noise. The latter approach is believed to have greater encryption potential than the temporal scrambling technique, in terms of the time needed to “break the secrecy code.” The encryption techniques are assessed on the basis of perceptual experiments, as well as by means of a quantitative assessment of speech-spectrum distortion, as given by an appropriate “distance” measure.