Rajeev Aggarwal, Jai Karan Singh, Vijay Kumar Gupta, Sanjay Rathore, Mukesh Tiwari, Dr.Anubhuti Khare International Journal of Computer Applications (0975 – 8887) Volume 20– No.5, April 2011 Presenter Chia-Cheng Chen 1

 Introduction  Multiresolution Analysis Using Filter Bank  Modifier Universal Threshold  Soft and Hard Thresholding  Results and Discussion 2

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 Discrete-wavelet transform (DWT) based algorithm are used for speech signal denoising. Here both hard and soft thresholding are used for denoising.  Analysis is done on noisy speech signal corrupted by babble noise at 0dB, 5dB, 10dB and 15dB SNR levels. 4

 The DWT uses Multi resolution filter banks and special wavelet filters for the analysis and reconstruction of signals.  It analyse the signal at different frequency bands with different resolutions, decompose the signal into a coarse approximation and detail information. 5

 Two-level wavelet decomposition tree 6

 Two-level wavelet reconstruction tree 7

 Wavelet thresholding is applied to the approximation coefficient (Vn-1) and detail coefficients (Wn,Wn-1). 8

 In this paper, we removed the babble noise from noisy signal which contain the noise contents of babble noise.  We want to find threshold value that will use to remove noise from noisy signal, but also recover the original signal efficiently. 9

 Developed by Donoho and Jonstone and it is called as universal threshold ◦ Where N denotes number of samples of noise and is standard deviation of noise. 10

 Again Universal threshold was modified with factor “k ‟ in order to obtain higher quality output signal: 11

 The soft and hard thresholding methods are used to estimate wavelet coefficients in wavelet threshold denoising. ◦ Hard thresholding ◦ Soft thresholding 12

13 Thr=0.4 Z = (-1, 1, 100)

 We implemented babble noise removal algorithm in Matlab (R2010a).  Speech signal is corrupted by babble noise at 0dB, 5dB, 10dB and 15dB SNR levels. 14

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 We choose 5-level DWT and db5 wavelet. Improved threshold value is obtained by replacing threshold “thr ‟ (2) with 16

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 Speech denoising is performed in wavelet domain by thresholding wavelet coefficients.  We found that by using modified universal threshold, we can get the better results of de-noising, especially for low level noise. 21