Jaehyung Lee

Sound source positioning using microphone array installed on a flying drone

This study presents an application of acoustic source localization using microphone array installed on a drone. Although recent technology of drone enables to record audio and video, there are still acoustic problems such as engine noise, propeller-induced flow noise, microphone directivity, etc. Such unwanted noise shows strong tonal characteristics with broad band noise contents. To acquire usable acoustic signal from array measurements while a drone is flying, we implemented acoustic signal conditioning and array processing. The approach to the problem is to adapt beamforming and TDOA techniques that provide localization capability of multiple sources and the position or direction of arrival of source, respectively. The array configuration and angle resolution are adjusted depending on the application requirements. We limit our attention to stable hovering condition to rule out position and heading error occurred by the drone motion. The experimental results of position estimation under a various noise...

Localization of acoustic source in windy environment using ray tracing

Position estimation of sound source using ray tracing method is introduced based on wind field measurement. TDOA (time difference of arrival) estimate error occurs during outdoor sound measurement due to the atmospheric condition such as wind, temperature, humidity and so on. Such condition can possibly change the trajectories of rays. It produces erroneous propagation time information accordingly. In this study, simplex method is used to estimate the source position using ray tracing. The basic concept is to find the estimation point which generates smallest mean square error of propagation distances or times from the candidate points. At first the estimation area is set around the first estimate which is calculated from the TDOA estimation. The simplex method is then applied to each point in the estimation area. Nelder-Mead simplex method is used to find the best position that produces the minimum error in travelling distances. In order to apply the ray tracing, the wind distribution is interpolated bas...

Experimental Study on Estimation of Flight Trajectory Using Ground Reflection and Comparison of Spectrogram and Cepstrogram Methods

A methodology is proposed to estimate a trajectory of a flying target and its velocity using the time and frequency analysis of the acoustic signal. The measurement of sound emitted from a flying acoustic source with a microphone above a ground shall receive both direct and ground-reflected sound waves. For certain frequency contents, the destructive interference happens in received signal waveform reflected path lengths are in multiple integers of direct path length. This phenomenon is referred to as the acoustical mirror effect and it can be observed in a spectrogram plot. The spectrogram of acoustic measurement for a flying vehicle measurement shows several orders of destructive interference curves. The first or second order of curve is used to find the best approximate path by using nonlinear least-square method. Simulated acoustic signal is generated for the condition of known geometric of a sensor and a source in flight. The estimation based on cepstrogram analysis provides more accurate estimate than spectrogram.

Estimation of Moving Target Trajectory using Optimal Smoothing Filter based on Beamforming Data

This paper presents an application of an optimal smoothing filter for moving target tracking problem based on measured noise source. In order to measure distance and velocity for the moving target, a beamforming method is applied to use the noise source by using microphone array. Also a Kalman filter and an optimal smoothing algorithm are adopted to improve accuracy of trajectory estimation by using a Singer target model. The simulation is conducted with a missile dynamics to verify performance of the optimal smoothing filter, and a model rocket is used for experiment environment to compare the trajectory estimation results between the beamforming, the Kalman filter, and the smoother. The Kalman filter results show better tracking performance than the beamforming technique, and the estimation results of the optimal smoother outperform the Kalman filter in terms of trajectory accuracy in the experiment results.

Position estimation of rotating sound source using Kalman filtering based on time difference of arrival measurements

In this work, we are interested in tracking a rotating sound source using a Kalman filtering technique based on a set of non-linear time difference of arrival (TDOA) measurements. Array of microphones measure acoustic signal emitted from a rotating source and the TDOA estimates are calculated followed by a solution for hyperbolic position fix. The position estimation of sound source based on TDOA is a popular technique in source localization. The method involves calculation of a set of nonlinear equations and poor accuracy of TDOA estimates often results in inaccuracy in location. In this work, the range difference is expressed by a model movement on which a recursive extended Kalman Filter has been developed. The TDOA measurements optimize the estimated values which are reduced as observation in extended Kalman filtering algorithm. Location estimation is updated from TDOA measurements along with the time history data. The Cramer-Rao Lower Bound (CRLB) is derived and simulations are compared. [Work suppor...

Design of three-dimensional microphone array on polyhedrons

The localization of sound sources in a three dimensional space has been recognized as an important research topic in acoustics. Many acoustic measurement techniques in three-dimensional space have used spherical shape of array to optimize sensor configuration and increase its performance and spatial resolution. In this study, the design of microphone array on polyhedral surfaces is proposed to introduce an easy way of building arrays and to achieve the measurement capability for all direction as a spherical array does. Five symmetrical polyhedrons are used and the simulation results are compared. MEMS microphones are used in arrays and the tests are made in an anechoic environment to validate the performance of arrays. MEMS sensor makes it easy to build a three-dimensional array and enables to implement large number of sensors in a small area. Sensors are built on a printed circuit board (PCB) which becomes a sub-array of polyhedrons. The array output is processed using conventional beamforming method to ...

Experimental study of synthetic aperture microphone array on rotor blade noise.

Recent development of signal processing technologies has encouraged the aero‐acousticians to implement the state‐of‐the‐art sensors and data acquisition devices. They sometimes cost too much; however, especially for the academic arenas, the efforts of reducing the expense of integrating a system and increasing performance of phased array have initiated the idea of designing the synthetic aperture microphone array. The application of beamforming technique in localizing rotor blade noise and the use of synthetic aperture array in wind tunnel testing are presented. To apply the synthetic aperture beamforming on rotating objects, three steps should be considered. The first step is to restore the original acoustic waveform radiated from a rotating sound source. The second step is to synthesize independent array measurement data by correcting phase information of the received acoustic signals. Finally, the beamformer calculates the power on each point of grid in the space. The paper describes the details of dep...

Study on 3D Sound Source Visualization Using Frequency Domain Beamforming Method

An approach to 3D visualization of multiple sound sources has been developed with the application of a moving array technique. Frequency domain beamforming algorithm is used to generate a beam power map and the sound source is modeled as a point source. When a conventional delay and sum beamformer is used, it is considered that 2D distribution of sensors leads to have deficiency in spatial resolution along a measurement distance. The goal of moving an array in this study is to form 3D array aperture surrounding multiple sound sources so that the improved spatial resolution in a virtual space can be expected. Numerical simulation was made to examine source localization capabilities of various shapes of array. The 3D beam power maps of hemispherical and spherical distribution are found to have very sharp resolution. For experiments, several sound sources were placed in the middle of defined virtual space and arc-shaped line array was rotated around the sources. It is observed that spherical array shows the most accurate determination of multiple sources` positions.

Experiments for the Acoustic Source Localization in 2D Cavity Flow

This paper presents an acoustic source localization technique on 2D cavity model in flow using a phased microphone array. Investigation was performed on cavity flows of open and closed types. The source distributions on 2D cavity flow were investigated in an anechoic open-jet wind tunnel. The array of microphones was placed outside the flow to measure the far field acoustic signals. The optimum sensor placement was decided by varying the relative location of the microphones to improve the spatial resolution. Pressure transducers were flush-mounted on the cavity surface to measure the near-filed pressures. It is shown that the propagated far field acoustic pressures are closely correlated to the near-field pressures and their spectral contents are affected by the cavity parameter L/D.