EURASIP Journal on Advances in Signal Processing, 2010, -94 pp.Significant knowledge about microphone arrays has been gained from years of intense research and product development. There have been numerous applications suggested, for example, from large arrays (in the order of 100 elements) for use in auditoriums to small arrays with only 2 or 3 elements for hearing aids and mobile telephones. Apart from that, microphone array technology has been widely applied in speech recognition, surveillance, and warfare. Traditional techniques that have been used for microphone arrays include fixed spatial filters, such as, frequency invariant beamformers, optimal and adaptive beamformers. These array techniques assume either model knowledge or calibration signal knowledge as well as localization information for their design. Thus they usually combine some form of localisation and tracking with the beamforming. Today contemporary techniques using blind signal separation (BSS) and time frequency masking technique have attracted significant attention. Those techniques are less reliant on array model and localization, but more on the statistical properties of speech signals such as sparseness, non-Gaussianity, and non-stationarity. The main advantage that multiple microphones add from a theoretical perspective is the spatial diversity, which is an effective tool to combat interference, reverberation, and noise. The underpinning physical feature used is a difference in coherence in the target field (speech signal) versus the noise field. Viewing the processing in this way one can understand also the difficulty in enhancing highly reverberant speech given that we only can observe the received microphone signals.
This special issue contains contributions to traditional areas of research such as frequency invariant beamforming [1], hand-free operation of microphone arrays in cars [2], and source localisation [3]. The contributions show new ways to study these traditional problems and give new insights into those problems. Small size arrays have always a lot of applications and interest for mobile terminals, hearing aids, and close up microphones [4]. The novel way to represent small size arrays leads to a capability to suppress multiple interferers. Abnormalities in noise and speech stemming from processing are largely unavoidable, and using nonlinear processing results often in significant character change particularly in noise character. It is thus important to provide new insights into those phenomena particularly the so called musical noise [5]. Finally, new and unusual use of microphone arrays is always interesting to see. Distributed microphone arrays in a sensor network [6] provide a novel approach to find snipers. This type of processing has good opportunities to grow in interest for new and improved applications.Microphone Array Speech Processing
Selective Frequency Invariant Uniform Circular Broadband Beamformer
First-Order Adaptive Azimuthal Null-Steering for the Suppression of Two Directional Interferers
Musical-Noise Analysis in Methods of Integrating Microphone Array and Spectral Subtraction Based on Higher-Order Statistics
Microphone Diversity Combining for In-Car Applications
DOA Estimation with Local-Peak-Weighted CSP
Shooter Localization in Wireless Microphone Networks
