Speech encryption using discrete orthogonal transforms

The performances of five discrete orthogonal transforms in speech encryption systems are compared. The transforms considered are the discrete Fourier transform, discrete cosine transform, Walsh-Hadamard transform, Karhunen-Loeve transform, and discrete prolate spheroidal transform. Four objective measures are used to grade the encryption systems with respect to residual intelligibility and recovered voice quality. A figure of merit based on all the four objective measures is formed. It gives good correlation to the subjective results of residual intelligibility and recovered speech quality