Quantitative estimation of improving speech quality by the isomorphic emphasis in spectrum scrambling encryption over poor radio channels

A new estimation method of speech quality is proposed based on Zwicker´s method to evaluate qualitative speech degradation when various encryptions are employed. The isomorphic emphasis previously reported by one of the authors is discussed in order to quantitatively evaluate the effect in improving speech quality over poor radio channels when encryption is employed. The improvement in speech quality by employing isomorphic emphasis over a radio channel with spectrum inversion is up to 12 dB according to both theoretical analysis and experimental results