Accurate Linear Prediction Coefficient (LPC) estimation is a central requirement in low bitrate voice coding. Under harsh acoustic conditions, LPC estimation can become unreliable. This results in poor quality of encoded speech and introduces annoying artifacts. The purpose of this thesis is to develop and test a two-branch speech enhancement preprocessing system. This system consists of two denoising blocks. One block will enhance the degraded speech for accurate LPC estimation. The second block will increase the perceptual quality of the speech to be coded. The goals of this research are two-fold-to design the second block, and to compare the performance of other denoising schemes in each of the two branches. Test results show that the two-branch system can provide better perceptual quality of coded speech over conventional one-branch (i.e., one denoising block) speech enhancement techniques under many noisy environments.

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