Research And Application For Technology Of Speech Enhancement

In the process of speech communication, the speech signal is often corrupted acoustically by ambient noise, electronic noise, or speech of other talkers. So a received speech signal is not pure, but noisy speech signal. For example, a speech signal caused by phones installed on plane, car or ship, public phones in the street or mobile phone is often disturbed by strong background noise. Therefore, speech enhancement technique plays a great pan of digtal speech signal processing.Speech enhancement is a process of filtering the noisy speech signal to improve its quality and performance of speech processing system, and to make speech clearer, more understood and more comfortable. Most practical speech enhancement systems composed of an accuracy noise estimator and good filter to reduce the noise.Classical methods of estimating noise are based on Voice Activity Detection (VAD) which is easy to be realized in practical. But the experiment results show that VAD has poor perfermance in the side of accurate estimate of noise. Another methods based on continuous renewal noise spectral greatly improve the accuracy of noise estimator without VAD. Particlularly, the latters have the excellent performance for fluctuating noise and obtain the good results in practical application.In the design of filter, classical methods are based on Short Time Spectral Analysis (STSA). In the past decades, many new methods are proposed, such as speech enhancement based on wavelet or Hidden Markov Model (HMM), acoustical characteristic, and so on. While these methods have still a long way for practical application. Recently, the principle of TURBO iteration idea developped rapidly in many fields: encoding, decoding, image filter, etc. In the thesis TURBO speech enhancement method based on TURBO iterative algorithm is proposed. The result obtained by computer simulation is satisfactory.The thesis places emphesis on research and application of speech enhancement technology, and proposes TURBO speech enhancement method, Following is the main work of this thesis:1. A variety of methods of noise estimate are discussed. And a comparation and the evalution of the results are given. An improved method based on the connection of two kinds of noise estimate is proposed.2. A variety of methods about speech enhancement are discussed. And TURBO speech enhancement based on TURBO iteration is propsed.3. Two speech enhancement systems composed of noise estimator and filter design based on STSA are designed, and the results for both simulated and real speech signal are given in the thesis.