Enhancement of coded speech by constrained optimization

A new method for the enhancement of speech signals contaminated by speech-correlated noise, such as that in the output of a speech coder, is presented. The method is based on constrained optimization of a criterion. We implement the method on a block-by-block basis and use two constraints. A first constraint ensures that the signal power is preserved. A modification constraint ensures that the power of the difference of the enhanced and unenhanced signal is less than a fraction of the power of the unenhanced signal. We apply the method to increase the periodicity of the speech signal. Noisy-sounding coded voiced speech generally has a high SNR and can be enhanced while satisfying a strict modification constraint. Sounds that are not nearly periodic are perceptually unaffected by the optimization because of the modification constraint. Practical results show that the method forms a powerful alternative to existing post-filter procedures.