Contents
1. INTRODUCTION .......................................................................................................... i 2. WAVE ATOM TRANSFORM ...................................................................................... 4 2.1 Definition of Wave Atom Transform ...................................................................... 4 2.2 1-D Characteristics in Wave Atom Transform ........................................................ 6 2.3 The Structure of 1-D filter-bank in Wave Atom……………………………….…10
3. THRESHOLDING METHOD FOR NOISE REDUCTION ...................................... 17 3.1 Hard and Soft Thresholdings ................................................................................ 17 3.2 Determination of Threshold .................................................................................. 20 4. EXPERIMENTS AND DISCUSSIONS……………………………………………..27 4.1Experimental Conditions…………………………………………………………27
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4.2 Results and Discussions ........................................................................................ 28 5.CONCLUSION ............................................................................................................ 37 REFERENCE .................................................................................................................. 38 ABSTRACT (IN KOREAN) .......................................................................................... 40
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1. INTRODUCTION
Speech is one of the most natural and convenient ways of intercommunication. Thus, speech signal processing techniques for a man-machine interface like speech recognition, speech synthesis and speech coding have drawn much attention. As speech processing moved from the laboratory to the field, it has become increasingly important to deal with the ambient noise. Since the quality and intelligibility are degraded by the ambient noise, the problem of reducing noise components of the noisy speech is still regarded as an important issue in the field of speech research [1-3].
Most classical methods for handling ambient wideband noise were variants of an approach based on subtracting an estimate of the spectrum of the noise from that of the noisy speech [4-7]. And then a novel approach for noise reduction using the wavelet transform has been proposed by D. L. Donoho [8]. It employs the thresholding technique in the wavelet domain and has shown to have good properties for a wide class of signals corrupted by additive white Gaussian noise. Over the past two decades, numerous signal processing techniques with the wavelet transform have been developed to make use of its superiority to the conventional Fourier transform.
Recently, wave atom transform has been proposed, and has shown its
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potential in denoising experiments on both seismic and fingerprint images [1]. Wave atom was introduced as a variant of 2D wavelet packets obeying the parabolic scaling. In a nutshell, wave atoms interpolate exactly between directional wavelets and Gabor, in the sense that the period of oscillations of each wave packet (wavelength) is linked to the size of the essential support (diameter) by the parabolic scaling, i.e., wavelength ~ (diameter)2 [1,2].
In this thesis, we apply the 1D wave atom transform to noisy speech signals for noise reduction. In the first place, we analyzed the algorithm of 1D wave atom transform in the signal processing point of view. Then, using thresholding methods for the wave atom coefficients of noisy speech signals, noise reduction experiments were performed for noisy speech having various signal-to-noise ratios. We also did the similar experiments using the wavelet transform to compare them with wave atom transform. Experimental results have shown that the wave atom transform gives somewhat better performance than the wavelet transform for noise reduction from noisy speech with additive Gaussian noise.
This thesis is organized as follows. Chapter 2 provides some background information on the 1D wave atom transform relating to the wave packet tree and filter-bank. Then thresholding methods for noise reduction are explained in chapter 3 with some preliminary experiments to determine the threshold. In chapter 4, noise reduction experimental results using the wave atom transform
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基于波原子变换的语音信号去噪毕业论文
