SRISESHUKUMAR BASAVA , pp. 66. ING/School of Engineering, 2012.
The use of microphone arrays to acquire and recognize speech in meetings (conference) poses several problems for speech processing as there exist many speakers within a small space, typically around a table. The necessity to design a suitable microphone array system with minimum noise and more efficient localization algorithms is drawing attention of researchers to work on it. Extensive research is being carried out on Microphone Array Beamforming to make the system, robust, viable and elegant for commercial use. This study is done with a similar objective.
A system consisting of 4 microphones arranged in linear array is setup in a simulated reverberant environment. Filter-and-sum beam forming is implemented both in time domain and frequency domain. A Wiener filter is chosen as post filtering technique. One of the main goals of the thesis is to improve the quality of the primary speech signal based on microphone array with Wiener beam forming (filter-and-sum beam forming with wiener post filtering). Weighted over lap add (WOLA) filter bank is also implemented as a part of frequency domain wiener beam forming to make use of subband beam forming. Also RLS algorithm is used to make the subband beamforming adaptive.
Speaker localization plays a pivotal role in the development of speech enhancement methods requiring information of the speaker position. Among many localization algorithms, Steered Response Power (SRP) with a combination of Phase Alignment Transform (PHAT) called SRP-PHAT has proved to be a robust one in many studies. Also as a part of this project, modeling of SRP-PHAT for detecting the speaker position for the above described system is done.
To evaluate the system performance, Signal-to-Noise-Ratio (SNR) is calculated for both original and beam formed signals. Perpetual Evaluation of Speech Quality (PESQ), an International Telecommunication Union (ITU-T) standard for evaluating quality in speech signals is used for determining the Mean opinion Score (MOS) for both the original and the beam formed signals.