Quality improvement of low-bit-rate noisy speech using the subspace method

Additive noise presents a particularly difficult problem for linear predictive-based speech coding (LPC) systems operating at sampling rates up to 4.8 kb/s. In this paper, the performance of cascade signal-subspace-based speech enhancement algorithm/ Code Excited Linear Predictive (CELP) coding system. is studied and Compared with the conventional cascade spectral-subtraction-based speech enhancement of algorithm/ CELP system. Both systems have been tested under the same conditions, 1, e. the same type of noise (white noise) and the same signal-to-noise-ratios. An LPC-based objective test is used for the evaluation of both systems. Based on this test, it is shown that the signal-subspace-based speech enhancement algorithm outperforms the spectral-subtraction-based speech enhancement algorithm such that it could be recommended as a preprocessor for cry LPC speech coding system.