Blind identification of acoustic systems and enhancement of reverberant speech

Imperial Users onl

Estimation of dominant sound source with three microphone array

Several real-life applications require a system that would reliably locate and track a single speaker. This can be achieved by using visual or audio data. Processing of an incoming signal to obtain the location of a source is known as Direction of Arrival (DOA) estimation. The basic setting in audio based DOA estimation is a set of microphones situated in known locations. The signal is captured by each of the microphones, and the signals are analyzed by one of the following methods: steered beamformer based method; subspace based method; or time delay estimation based method. The aim of this thesis is to review different classes of existing methods for DOA estimation and to create an application for visualizing the dominant sound source direction around a three-microphone array in real time. In practice, the objective is to enhance an algorithm for a DOA estimation proposed by Nokia Research Center. As visualization of dominant sound source creates a basis for many audio related applications, a practical example of such applications is developed. The proposed algorithm is based on time delay estimation method and utilizes cross correlation. Several enhancements are developed to the initial algorithm to improve its performance. The proposed algorithm is evaluated by comparing it with one of the most common methods, general cross correlation with phase transform (GCC PHAT). The evaluation includes testing all algorithms on three types of signals: speech signal arriving from a stationary location, speech signal arriving from a moving source, and a transient signal. Additionally, using the proposed algorithm, a computer application with a video tracker is developed. The results show that the initially proposed algorithm does not perform as well as GCC PHAT. The enhancements improve the algorithm performance notably, although they did not bring the efficiency of the algorithm to the level of GCC PHAT when processing speech signals. In case of transient signals, the enhanced algorithm was superior to GCC PHAT. The video tracker was able to successfully track the dominant sound source

Localization of wireless communication emitters using Time Difference of Arrival (TDOA) methods in noisy channels

The ability to provide position information of wireless emitters comprises a very important communication tool and has extremely valuable applications to military as well as civilian life. GSM is the most popular method of modulation adopted around the world, for mobile telephony. This thesis is focused on the Time Difference Of Arrival (TDOA) estimation, applied to GSM signals, in noisy channels. Improvements in denoising, in conjunction with wavelet processing, are proposed for estimating the TDOA of signals received at two spatially separated sensors. Wavelet denoising based on a modified maximum likelihood method and a higher order moment method is proposed, to improve the performance. A numerical evaluation of the methods, when unequal SNR conditions prevail, is presented. The performance of the proposed denoising methods in a jamming environment is also addressed. Simple excision schemes to improve the performance when jamming is present, are evaluated. Simulation results indicate good performance of the methods and improved estimates relative to the ones obtained using no denoising. Jamming presence degrades the performance but still the extracted estimates are improved.http://archive.org/details/localizationofwi109452507Hellenic Navy autho