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Advances in Acoustics and Vibration
Volume 2014, Article ID 765454, 11 pages
Research Article

Subband DCT and EMD Based Hybrid Soft Thresholding for Speech Enhancement

1Graduate School of Information Science and Technology, The University of Tokyo, Tokyo 113-8656, Japan
2Department of Computer Science and Engineering, The University of Rajshahi, Rajshahi 6205, Bangladesh
3Graduate School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan
4Department of Electrical and Electronic Engineering, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh

Received 5 February 2014; Accepted 17 April 2014; Published 20 May 2014

Academic Editor: Rama B. Bhat

Copyright © 2014 Erhan Deger et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


This paper presents a two-stage soft thresholding algorithm based on discrete cosine transform (DCT) and empirical mode decomposition (EMD). In the first stage, noisy speech is decomposed into eight frequency bands and a specific noise variance is calculated for each one. Based on this variance, each band is denoised using soft thresholding in DCT domain. The remaining noise is eliminated in the second stage through a time domain soft thresholding strategy adapted to the intrinsic mode functions (IMFs) derived by applying EMD on the signal obtained from the first stage processing. Significantly better SNR improvement and perceptual speech quality results for different noise types prove the superiority of the proposed algorithm over recently reported techniques.