Konrad Kowalczyk

Konrad Kowalczyk
AGH University of Science and Technology in Kraków | AGH

Associate Professor in Signal Processing

About

61
Publications
14,609
Reads
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872
Citations
Additional affiliations
January 2015 - July 2020
AGH University of Science and Technology in Kraków
Position
  • Professor (Associate)
January 2012 - December 2014
Fraunhofer Institute for Integrated Circuits IIS
Position
  • Research Associate
June 2009 - December 2011
Friedrich-Alexander-University of Erlangen-Nürnberg
Position
  • Postdoctoral Research Fellow

Publications

Publications (61)
Article
Full-text available
The domain of spatial audio comprises methods for capturing, processing, and reproducing audio content that contains spatial information. Data-based methods are those that operate directly on the spatial information carried by audio signals. This is in contrast to model-based methods, which impose spatial information from, for example, metadata lik...
Conference Paper
Full-text available
Sound source localization (SSL) is an actively researched topic in the field of multichannel audio signal processing with numerous practical applications. Since it is used in different acoustic contexts, ensuring a good generalization of the techniques and models to various acoustic signals and environments is of great importance. In this paper, we...
Conference Paper
In various classification tasks the major challenge is in generating discriminative representation of classes. By proper selection of deep neural network (DNN) loss function we can encourage it to produce embeddings with increased inter-class separation and smaller intra-class distances. In this paper, we develop softmax-based cross-entropy loss fu...
Preprint
Many signal processing algorithms for distributed sensors are capable of improving their performance if the positions of sensors are known. In this paper, we focus on estimators for inferring the relative geometry of distributed arrays and sources, i.e. the setup geometry up to a scaling factor. Firstly, we present the Maximum Likelihood estimator...
Article
No PDF available ABSTRACT High mobility and an ability of gathering data from large terrains makes Unmanned Aerial Vehicles (UAVs) an excellent platform for placing visual or acoustic sensors. One recently emerging application of UAVs is search and rescue operation, during which drones are used to localize people in distress. A common approach to d...
Article
In acoustic environments the microphones capture a source signal corrupted by room reverberation and noise. This letter presents two optimum spatial filters which jointly reduce late reverberation and noise for the sound source recorded from distance in a reverberant room. The proposed rake filters are derived by incorporating spatial information a...
Article
Collaborative processing of signals recorded by distributed sensors brings about new opportunities as well as challenges to classical array signal processing. In this letter, we present a method for passive self-calibration of a distributed system in which each distributed node consists of an array of sensors. The proposed method estimates the posi...
Conference Paper
Acoustic event classification is of interest for various audio applications. The aim of this paper is to investigate the usage of a number of speech and audio based features in the task of acoustic event classification. Several features that originate from audio signal analysis are compared with features typically used in speech processing such as...
Conference Paper
Enhancing speech from audio signals recorded using several microphones is of interest to many audio applications such as human-computer interfaces and teleconference systems. With an increasing availability of low-cost micro-electro-mechanical systems (MEMS) and powerful processing units, embedded systems are capable of recording and processing sev...
Article
Full-text available
Due to its efficiency and simplicity, the finite difference time domain method is becoming a popular choice for solving wideband, transient problems in various fields of acoustics. So far, the issue of extracting a binaural response from finite difference simulations has only been discussed in the context of embedding a listener geometry in the gri...
Article
Full-text available
Flexible and efficient spatial sound acquisition and subsequent processing are of paramount importance in communication and assisted listening devices such as mobile phones, hearing aids, smart TVs, and emerging wearable devices (e.g., smart watches and glasses). In application scenarios where the number of sound sources quickly varies, sources mov...
Article
Full-text available
Human perception of room acoustics depends among others on the time of transition from early reflections to late reverberation in room impulse responses, which is known as mixing time. In this letter, a multi-channel mixing time prediction method is proposed, which in contrast to state-of-the-art channel-based predictors accounts for spatiotemporal...
Conference Paper
Full-text available
The finite difference time domain method has direct applications in musical instrument modeling, simulation of environmental acoustics, room acoustics and sound reproduction paradigms, all of which benefit from auralization. However, rendering binaural impulse responses from simulated data is not straightforward to accomplish as the calculated pres...
Conference Paper
Spatial sound acquisition aims at capturing the sound field such that spatial cues present in the sound scene at the recording side are preserved at the reproduction side. The virtual microphone technique is a spatial recording method that allows for an arbitrary selection of the recording position and orientation. It exploits the parametric inform...
Conference Paper
In digital cameras, zooming allows for narrowing the apparent angle of view in a video or an image. When sounds compliment the visual information, a desirable function would be to provide an acoustical zoom which is aligned with the zoomed visual image. In this paper, an approach is presented to achieve such a zoom effect using a microphone array....
Conference Paper
Acoustic source localization and tracking (ASLT) in reverberant environments is a challenging task due to the multi-path propagation of acoustic waves. ASLT is often based on the use of a Kalman filter or a particle filter, with time-difference-of-arrival (TDOA) estimates used as measurements. In this work, we aim to track non-concurrent speakers b...
Conference Paper
The mixing time is an important parameter in the human perception of room acoustics. It is defined as the time instant of room impulse responses (RIRs) when coherent early reflections dissolve into diffuse reverberation. Most common mixing time estimation methods statistically analyze a single RIR by measuring the density of reflections or the degr...
Article
Estimating the geometric and reflective properties of the environment is important for a wide range of applications of space-time audio processing, from acoustic scene analysis to room equalization and spatial audio rendering. In this manuscript, we propose a methodology for frequency-subband in-situ estimation of the reflection coefficients of pla...
Article
The knowledge of parameters characterizing an acoustic environment, such as the geometric information about a room, can be used to enhance the performance of several audio applications. In this paper, a novel method for three-dimensional room geometry inference based on robust and high-resolution beamforming techniques for spherical microphone arra...
Conference Paper
In hands-free communication applications, the main goal is to capture desired sounds, while reducing noise and interfering sounds. However, for natural-sounding telepresence systems, the spatial sound image should also be preserved. Using a recently proposed method for generating the signal of a virtual microphone (VM), one can recreate the sound i...
Conference Paper
Spatial sound acquisition methods typically capture the sound scene with reference to the position of the recording device. Using a recently proposed virtual microphone (VM) technique, the position and characteristics of the recording device (such as the directivity response and orientation) can be modified. This technique relies on synthesizing a...
Article
Full-text available
Localization of early room reflections can be achieved by estimating the time-differences-of-arrival (TDOAs) of reflected waves between elements of a microphone array. For an unknown source, we propose to apply sparse blind system identification (BSI) methods to identify the acoustic impulse responses, from which the TDOAs of temporally sparse refl...
Conference Paper
Full-text available
This paper presents a novel model-based method for in-situ esti-mation of sound reflection coefficients in acoustic enclosures. The method uses a modeling engine for simulation of acoustic propaga-tion and generation of the spatial pseudospectrum using a beamform-ing technique. The simulated pseudospectrum is matched with the measured pseudospectru...
Article
This paper presents an experimental and comparative study of several spherical microphone array eigenbeam (EB) processing techniques for localization of early reflections in room acoustic environments, which is a relevant research topic in both audio signal processing and room acoustics. This paper focuses on steered beamformer-based and subspace-b...
Article
Recent works have shown that precise localization of dominant reflections in acoustic environments can be achieved even by relatively small arrays if advanced beamforming concepts are employed. To this end subspace-based and steered beamformers-based localization techniques are implemented in the so-called eigenbeam domain leading to eigenbeam (EB)...
Conference Paper
Full-text available
SCENIC is an EC-funded project aimed at developing a harmonized corpus of methodologies for environmentaware acoustic sensing and rendering. The project focusses on space-time acoustic processing solutions that do not just accommodate the environment in the modeling process but that make the environment help towards achieving the goal at hand. The...
Conference Paper
Full-text available
The SCENIC project is aimed at making the environment become an integral part of the acoustic system. The goal is to boost the performance of arrays of speakers and microphones and, in some cases, to enable applications that would not be possible otherwise. This paper describes how this can be achieved.
Conference Paper
Full-text available
Methods of 3D direction of arrival (DOA) estimation, coherent source detection and reflective surface localization are studied, based on recordings by a spherical microphone array. First, the spherical harmonics domain minimum variance distortionless response (EB-MVDR) beamformer is employed for the localization of broadband coherent sources, which...
Conference Paper
Full-text available
This paper presents a method for the localization of reflectors in an acoustic environment, using robust beamforming techniques and a cylindrical microphone array, for which an intuitive and highly efficient three-step procedure is proposed. First, the directions of arrival (DOAs) corresponding to the sound source and reflectors are estimated by a...
Article
Full-text available
In this paper, a method for modeling diffusive boundaries in finite-difference time-domain (FDTD) room acoustics simulations with the use of impedance filters is presented. The proposed technique is based on the concept of phase grating diffusers, and realized by designing boundary impedance filters from normal-incidence reflection filters with add...
Article
Full-text available
This paper presents methods for simulating room acoustics using the finite-difference time-domain (FDTD) technique, focusing on boundary and medium modeling. A family of nonstaggered 3-D compact explicit FDTD schemes is analyzed in terms of stability, accuracy, and computational efficiency, and the most accurate and isotropic schemes based on a rec...
Conference Paper
Full-text available
Compact explicit schemes are an attractive alternative to more conventional finite difference schemes such as Yee's classical staggered scheme, because they allow reducing the numerical dispersion error and increasing the effective bandwidth. In order to use these schemes for the simulation of room acoustics, numerical formulation of frequency-depe...
Article
Full-text available
This paper presents a comparative study of several tech-niques that are applicable to the localization of the most significant reflectors in an acoustic environment. It focuses on subspace-based and steered beamformer-based localiza-tion techniques and includes eigenbeam (EB)-ESPRIT, EB-MUSIC, and EB-minimum variance distortionless response (EB-MVD...
Conference Paper
Full-text available
This paper aims at providing a better insight into the 3D approximations of the wave equation using compact finite-difference time-domain (FDTD) schemes in the context of room acoustic simulations. A general family of 3D compact explicit and implicit schemes based on a nonstaggered rectilinear grid is analyzed in terms of stability, numerical error...
Conference Paper
Full-text available
In this paper, a method for modeling diffusion caused by non-smooth boundary surfaces in simulations of room acoustics using finite difference time domain (FDTD) technique is investigated. The proposed approach adopts the well-known theory of phase grating diffusers to efficiently model sound scattering from rough surfaces. The variation of diffuse...
Article
Full-text available
In this paper, a complete method for finite-difference time-domain modeling of rooms in 2-D using compact explicit schemes is presented. A family of interpolated schemes using a rectilinear, nonstaggered grid is reviewed, and the most accurate and isotropic schemes are identified. Frequency-dependent boundaries are modeled using a digital impedance...
Article
Full-text available
In this paper, we present new methods for constructing and analysing formulations of locally reacting surfaces that can be used in finite difference time domain (FDTD) simulations of acoustic spaces. Novel FDTD formulations of frequency-independent and simple frequency-dependent impedance boundaries are proposed for 2D and 3D acoustic systems, incl...
Conference Paper
Full-text available
This paper discusses compact-stencil finite difference time domain (FDTD) schemes for approximating the 2D wave equation in the context of digital audio. Stability, accuracy, and efficiency are investigated and new ways of viewing and interpreting the results are discussed. It is shown that if a tight accuracy constraint is ap-plied, implicit schem...
Article
Full-text available
A new method for modeling frequency-dependent boundaries in finite-difference time-domain (FDTD) and Kirchhoff variable digital waveguide mesh (K-DWM) room acoustics simulations is presented. The proposed approach allows the direct incorporation of a digital impedance filter (DIF) in the multidimensional (2D or 3D) FDTD boundary model of a locally...
Data
Full-text available
This paper presents a new method for modelling frequency-dependent boundaries in finite difference time domain (FDTD) and Kirchhoff variable digital waveguide mesh (K-DWM) room acoustics simulations. The proposed approach allows direct incorporation of a digital impedance filter (DIF) in the multi-dimensional (i.e. 2D or 3D) FDTD boundary model of...
Conference Paper
Full-text available
In this paper, we present new methods for constructing and analysing frequency-dependent boundaries in room acoustic modelling with the use of finite difference time domain (FDTD) techniques. Novel FDTD formulations of simple locally reacting wall models with complex impedance are proposed and analysed in terms of pressure wave reflectance for diff...
Conference Paper
Full-text available
This paper presents a method for on-line simulation of 2D resonators with reduced direction-dependent frequency error. The use of a compact implicit finite difference (FD) technique is proposed to reduce the dispersion error remarkably. In particular, a computationally efficient method that allows solving 2D implicit problems with a set of three-di...
Conference Paper
Full-text available
This paper presents a new model for modelling locally reacting walls, that can be used in finite difference modelling of acoustic spaces. The new 2D/3D finite difference boundary formulation is compared to the more conventional 1D formulation in terms of pressure wave reflection for different wall impedances and angles of incidence. The results sho...