Beamforming in near-field - metaheuristic approach and experimental tests in an anechoic chamber

A set of microphones spatially arranged in space in a specific pattern is called a microphone array. It can be used to extract and enhance the signal of interest from its observation corrupted by other interfering signals, such as noise or to estimate the direction of arrival of a source. In this paper we focus on a problem in which the desired signal (speech signal) is interfered by other signal with fully overlapping bandwidth but with different localization. Our goal is to attenuate the interfering signal. We experimentally study the method in which microphones do not have to be equally spaced and all information regarding signal phase is hidden in a transfer function of the microphone. We focus on determining the microphones positions and FIR filter coefficients so that the actual output the beamformer is as close as possible to the desired one (the level of speech signal remains unchanged, while the interfering signal is attenuated) in the sense of  norm. To solve this problem, we use a metaheuristic algorithm. Next, we construct the array and make an experiment in anechoic chamber. The initial results of the experiment show that the proposed method can be applied for array designing

Design of Fixed Wideband Beamformer through Improved Maximum Energy Approach

A maximum energy approach is investigated in this paper to design fixed wideband beamformer. This approach has been improved by integrating response variation (RV) into the target function to maintain the frequency invariant property of wideband beamformer over the whole passband. Two methods for designing null to suppress interference signal also have been proposed to make the wideband beamformer robust in complicated environment. Comparisons among other methods are provided to illustrate the effectiveness and enhancement of performance of the new approaches

On the indoor beamformer design with reverberation

Beamforming remains to be an important technique for signal enhancement. For applications in open space, the transfer function describing waves propagation has an explicit expression, which can be employed for beamformer design. However, the function becomes very complex in an indoor environment due to the effects of reverberation. In this paper, this problem is discussed. A method based on the image source method (ISM) is applied to model the room impulse responses (RIRs), which will act as the transfer function between source and sensor. The indoor beamformer design problem is formulated as a minimax optimization problem. We propose and study several optimization models based on the -norm to design the beamformer. We found that it is advantageous to separate early and late reverberations in the design process and better designs can be achieved. Several numerical experiments are presented using both simulated data and real recordings to evaluate the proposed methods

MICROPHONE ARRAY OPTIMIZATION IN IMMERSIVE ENVIRONMENTS

The complex relationship between array gain patterns and microphone distributions limits the application of traditional optimization algorithms on irregular arrays, which show enhanced beamforming performance for human speech capture in immersive environments. This work analyzes the relationship between irregular microphone geometries and spatial filtering performance with statistical methods. Novel geometry descriptors are developed to capture the properties of irregular microphone distributions showing their impact on array performance. General guidelines and optimization methods for regular and irregular array design are proposed in immersive (near-field) environments to obtain superior beamforming ability for speech applications. Optimization times are greatly reduced through the objective function rules using performance-based geometric descriptions of microphone distributions that circumvent direct array gain computations over the space of interest. In addition, probabilistic descriptions of acoustic scenes are introduced to incorporate various levels of prior knowledge for the source distribution. To verify the effectiveness of the proposed optimization methods, simulated gain patterns and real SNR results of the optimized arrays are compared to corresponding traditional regular arrays and arrays obtained from direct exhaustive searching methods. Results show large SNR enhancements for the optimized arrays over arbitrary randomly generated arrays and regular arrays, especially at low microphone densities. The rapid convergence and acceptable processing times observed during the experiments establish the feasibility of proposed optimization methods for array geometry design in immersive environments where rapid deployment is required with limited knowledge of the acoustic scene, such as in mobile platforms and audio surveillance applications

LOCALIZATION OF STATIONARY SOURCE OF FLOOR VIBRATION USING THE STEERED RESPONSE POWER METHOD

If the generated vibration in a building exceeds the acceptable limit design for a floor system, it is necessary to identify the source of vibration, a process known as localization. The objective of this study is the localization of stationary vibration sources, and the approach used is the steered response power (SRP) method. This method has already been shown to work well for wireless and acoustical applications to locate transmitter and sound sources, respectively. To the writer’s knowledge, this study is the first application of the SRP method to locate vibration sources using floor vibration measurements. However, because waves behave differently when propagated through a concrete floor as opposed to the air, this method has been significantly modified for the application presented herein. The key and prerequisite parameter for most vibration-sensing-localization approaches is wave propagation speed (WPS). The accuracy of these approaches therefore depends on the accuracy of the WPS estimate. The WPS of a concrete floor system is a function of parameters with high variability due to the mechanical and dynamic properties of the floor. This makes the task of vibration-sensing-localization challenging for the aforementioned approaches. The SRP method has been employed because it is based on an algorithm to post-process all received signals together and such structural variability is less likely to affect the accuracy; therefore, the SRP method is more robust. Most localization approaches are based on ideal wave propagation, e.g., constant propagation speed in all directions and vibration energy decreasing predictably as the source-sensor distance increases. However, such ideal propagation does not occur in many real-world structural systems such as a concrete floor. In this study, the WPS was estimated empirically in orthogonal directions using the cross-correlation function. The SRP method used herein was adopted to use the estimated WPS in orthogonal directions as an input parameter and then automatically interpolating the corresponding propagation speed for all other directions. This is another advantage of this method over existing methods. The experiment was conducted on the second floor of a full-scale, concrete-framed building at the University of Kentucky. The WPS was estimated in orthogonal directions using an electrodynamic shaker and seven accelerometers. The shaker applied an excitation force and acted as the source of vibration, and the accelerometers were put in various locations on the floor and measured the response. Using the estimated WPS and corresponding measurement data, the SRP method was able to locate the vibration source within 2.0 m in a floor approximately 13.4 m by 8.4 m in size