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  • 1.
    Bahne, Adrian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Brännmark, Lars-Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Improved loudspeaker-room equalization for stereo systems regarding channel similarity2012In: Proceedings - International Conference on Audio, Language and Image Processing, 2012, p. 254-259Conference paper (Refereed)
    Abstract [en]

    In this paper, a new approach to robust singlechannel loudspeaker-room equalization for stereo systems based on psychoacoustic insights is presented. Traditionally, in single-channel equalization each channel is equalized individually according to a desired target. In case the target cannot be reached for at least one of the two channels, this approach results in different loudspeaker-room transfer functions of the two channels at the listening position. However, reproducing the intended sound image of stereo recordings requires equal acoustic transfer functions from the input to the two loudspeakers to the listening region. In this paper we aim not only at equalizing the individual channels according to a desired target, but also at explicitly requiring symmetry between the two channels of a stereo system. To this end we propose a two-channel similarity SIMO controller structure, which is an extension to an earlier approach by the authors. The new approach is evaluated based on measurements in a room and is found to reduce differences between the room transfer functions of the two channels in both frequency and time domain.

  • 2.
    Bahne, Adrian
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Brännmark, Lars-Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Symmetric loudspeaker-room equalization utilizing a pairwise channel similarity criterion2013In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 61, no 24, p. 6276-6290Article in journal (Refereed)
    Abstract [en]

    Similarity of the room transfer functions (RTFs) of symmetric channel pairs is crucial for correct sound reproduction of, for example, stereophonic or 5.1 surround multichannel recordings. This physical and psychoacoustical insight yielded the filter design framework presented in this paper. The filter design framework introduced is based on MIMO feedforward control. It has the aim of pairwise equalization of two audio channels and incorporates two features. In the first place, each channel is individually equalized by minimizing the difference between a desired target response and the original RTF by means of support loudspeakers. The second and novel feature represents the similarity requirement and aims at minimizing the difference between the compensated RTFs of the two channels. In order to asses the proposed method a measure of RTF similarity is proposed. Tests with measurements of two different multichannel audio systems proved the method to be able to significantly improve the similarity of two RTFs.

  • 3.
    Barkefors, Annea
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Brännmark, Lars-Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Design and Analysis of Linear Quadratic Gaussian Feedforward Controllers for Active Noise Control2014In: IEEE Transactions on Audio, Speech, and Language Processing, ISSN 1558-7916, E-ISSN 1558-7924, Vol. 22, no 12, p. 1777-1791Article in journal (Refereed)
    Abstract [en]

    A method for sound field control applied to active noise control is presented and evaluated. The method uses Linear Quadratic Gaussian (LQG) feedforward control to find a Minimal Mean Square Error (MMSE)-optimal linear sound field controller under a causality constraint. It is obtained by solving a polynomial matrix spectral factorization and a linear (Diophantine) polynomial matrix equation. An important component in the design is the control signal penalty term of the criterion. Its use and influence is here discussed and evaluated using measured room impulse responses. The results indicate that the use of a relatively simple, frequency-weighted penalty on individual control signals provides most of the benefits obtainable by the considered more advanced alternative. We also introduce and illustrate several tools for performance analysis. An analytical expression for the attainable performance clearly reveals the performance loss generated by having to use a causal controller instead of the ideal noncausal controller. This loss is largest at low frequencies. Furthermore, we introduce a measure of the reproducibility of the target noise sound field with given control loudspeaker setups and room transfer functions. It describes how well a controller that uses an input subspace of dimension equal to the effective rank of the system is able to reproduce a target sound field. This performance measure can e.g. be used to support the selection of good combinations of placements of control loudspeakers.

  • 4.
    Berthilsson, Simon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Barkefors, Annea
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Brännmark, Lars-Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Acoustical zone reproduction for car interiors using a MIMO MSE framework.2012In: AES 48th International Conference, Munich, Germany, 2012Conference paper (Refereed)
  • 5.
    Brännmark, Lars-Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Robust audio precompensation with probabilistic modeling of transfer function variability2009In: 2009 IEEE Workshop on Applications of Signal Processing to Audio and Acoustics (WASPAA2009), New York City, NY, 2009Conference paper (Refereed)
  • 6.
    Brännmark, Lars-Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group. Dirac AB, Uppsala.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Multichannel Room Correction with Focus Control2015In: Journal of The Audio Engineering Society, ISSN 0004-7554, ISSN 1549-4950, Vol. 63, no 1-2, p. 21-30Article in journal (Refereed)
    Abstract [en]

    Digital equalization of audio systems is mostly performed on a channel-by-channel basis, i.e., loudspeakers are equalized separately and independently of each other. In reverberant rooms the spatial variability of the loudspeaker room transfer function puts a limit on what can be achieved with such single-channel approaches, and considerably more far-reaching results can be obtained with multichannel methods. In this paper we present a multichannel equalizer design method where the loudspeaker to be equalized is assisted by several support loudspeakers that act in combination to improve the response of the main loudspeaker while suppressing the reverberation of the listening room. However, since a full dereverberation may not always be desirable, we shall here study the proposed method from the perspective of how to control the amount of room correction for a given number of contributing support loudspeakers. The amount of correction is controlled by a scalar parameter that we interpret as a "focus control," enabling the user to slide seamlessly between a single-channel equalizer and a full multichannel inversion of the room.

  • 7.
    Brännmark, Lars-Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Robust loudspeaker equalization based on position-independent excess phase modeling2008In: 2008 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING, VOLS 1-12, 2008, p. 385-388Conference paper (Refereed)
    Abstract [en]

    A well known problem in loudspeaker equalization is that mixed phase design of the inverse filter causes residual "pre-ringings" in the equalized system, due to the spatial variability of loudspeakerroom transfer functions. A common strategy for robust and perceptually acceptable equalization is therefore to use minimum phase filters only. In this paper, a method for cautious mixed phase equalization is proposed. By analysis of a set of room transfer functions, it is concluded that some non-minimum phase zeros are insensitive to receiver position, and can therefore be robustly inverted. The method improves upon a minimum phase equalization by extending the minimum phase model with a robustly invertible all pass link. Validation measurements show that the time-domain aspect of equalization is improved throughout the spatial region of interest, while preringings are kept at a very low and prespecified level.

  • 8.
    Brännmark, Lars-Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Spatially robust audio compensation based on SIMO feedforward control2009In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 57, no 5, p. 1689-1702Article in journal (Refereed)
    Abstract [en]

    This paper introduces a single-input multiple-output (SIMO) feedforward approach to the single-channel loudspeaker equalization problem. Using a polynomial multivariable control framework, a spatially robust equalizer is derived base on a set of room transfer functions (RTFs) and a multipoint mean-square error (MSE) criterion. In contrast to earlier multipoint methods, the polynomial approach provides analytical expressions for the optimum filter, involving the RTF polynomials and certain spatial averages thereof. However, a direct use of the optimum solution is questionable from a perceptual point of view. Despite its multipoint MSE optimality, the filter exhibits similar, albeit less severe, problems as those encountered in nonrobust single-point designs. First, in the case of mixed phase design it is shown to cause residual "pre-ringings" and undesirable magnitude distortion in the equalized system. Second, due to insufficient spatial averaging when using a limited number of RTFs in the design, the filter is overfitted to the chosen set of measurement points, thus providing insufficient robustness. A remedy to these two problems is proposed, based on a   constrained MSE design and a method for clustering of RTF zeros. The outcome is a mixed phase compensator with a time-domain performance preferable to that of the original unconstrained design.

  • 9.
    Brännmark, Lars-Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Variable control of the pre-response error in mixed phase audio precompensation2009In: 2009 IEEE Workshop on Applications of Signal Processing to Audio and Acoustics (WASPAA 2009), New York CIty, NY, 2009Conference paper (Refereed)
  • 10.
    Brännmark, Lars-Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Bahne, Adrian
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Compensation of Loudspeaker-Room Responses in a Robust MIMO Control Framework2013In: IEEE Transactions on Audio, Speech, and Language Processing, ISSN 1558-7916, E-ISSN 1558-7924, Vol. 21, no 6, p. 1201-1216Article in journal (Refereed)
    Abstract [en]

    A new multichannel approach to robust broadband loudspeaker-room equalization is presented. Traditionally, the equalization (or room correction) problem has been treated primarily by single-channel methods, where loudspeaker input signals are prefiltered individually by separate scalar filters. Single-channel methods are generally able to improve the average spectral flatness of the acoustic transfer functions in a listening region, but they cannot reduce the variability of the transfer functions within the region. Most modern audio reproduction systems, however, contain two or more loudspeakers, and in this paper we aim at improving the equalization performance by using all available loudspeakers jointly. To this end we propose a polynomial based MIMO formulation of the equalization problem. The new approach, which is a generalization of an earlier single-channel approach by the authors, is found to reduce the average reproduction error and the transfer function variability over a region in space. Moreover, pre-ringing artifacts are avoided, and the reproduction error below 1000 Hz is significantly reduced with an amount that scales with the number of loudspeakers used.

  • 11.
    Brännmark, Lars-Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Bahne, Adrian
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Improved loudspeaker-room equalization using multiple loudspeakers and MIMO feedforward control2012In: Acoustics, Speech and Signal Processing (ICASSP), 2012 IEEE International Conference, 2012, p. 237-240Conference paper (Refereed)
    Abstract [en]

    In this paper, a new multichannel approach to robust loudspeaker-room equalization is presented. Traditionally, the equalization (or room correction) problem has been treated mostly by single-channel methods, with loudspeaker signals being prefiltered individually by separate scalar filters. Single-channel methods can generally improve the average spectral flatness of the acoustic transfer functions in a listening region, but the variability of the transfer functions within the region cannot be affected. Most modern audio reproduction systems, however, contain two or more loudspeakers, and in this paper we aim at improving the equalization performance by using all available loudspeakers jointly. To this end we propose a general MIMO formulation of the problem, which is a multichannel generalization of an earlier single-channel approach by the authors. The new approach is found to reduce the average reproduction error and the spatial variability of the acoustic transfer functions. Moreover, pre-ringing artifacts are avoided, and the reproduction error below 1000 Hz is significantly reduced with an amount that scales with the number of loudspeakers used.

  • 12.
    Brännmark, Lars-Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Controlling the impulse responses and the spatial variability in digital loudspeaker-room correction2015Conference paper (Refereed)
  • 13.
    Bárdoš, Ladislav
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baránková, Hana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cold Atmospheric Plasma Deposition of Diamond2007In: Plasma Processes and Polymers, ISSN 1612-8850, Vol. 4, no 5, p. 511-514Article in journal (Refereed)
    Abstract [en]

    Nanocluster diamonds can be synthesized in open air on stainless steel and molybdenum substrates with a hybrid cold atmospheric plasma source using air plasma and an air + alcohol mixture. At microwave powers below 300 W and at gas flow rates below 300 sccm the temperature of a thermally insulated steel substrate placed 1.5 cm from the hollow cathode caused by the air plasma were less than 600 °C. 200 nm thick coatings with nanocluster diamond grains and aggregates exhibiting diamond peaks in the Raman spectra at 1 325 cm-1 on stainless steel and at 1 322 cm-1 on Mo were formed after 1 h on untreated substrates.

  • 14.
    Johansson, Mathias
    et al.
    Dirac Research AB, Uppsala.
    Brännmark, Lars-Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Bahne, Adrian
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sound field control using a limited number of loudspeakers2009In: 36th Audio Engineering Society International Conference 2009: Automotive Audio - Sound in Motion, Dearborn, Michigan, Red Hook, NY: Audio-Engineering Society , 2009Conference paper (Refereed)
  • 15.
    Lingvall, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Brännmark, Lars-Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Multiple-point statistical room correction for audio reproduction: Minimum mean square error correction filtering2009In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 125, no 4, p. 2121-2128Article in journal (Refereed)
    Abstract [en]

    This paper treats the problem of correction of loudspeaker and room responses using a single source. The objective is to obtain a linear correction filter, which is robust with respect to listener movement within a predefined region-of-interest. The correction filter is based   on estimated impulse responses, obtained at several positions, and a linear minimum mean squared error criteria. The impulse responses are estimated using a Bayesian approach that takes both model errors and measurement noise into account, which results in reliable impulse response estimates and a measure of the estimation errors. The correction filter is then constructed by using information from both the estimated impulse response coefficients and their associated estimation errors. Furthermore, in the optimization criteria a time-dependent reflection filter is introduced, which attenuates the high frequency parts of the reflected responses, that is, the parts of the responses that cannot be compensated with a single source system. The resulting correction filter is shown to significantly improve both   the temporal and spectral properties of the responses compared to the uncorrected system, and, furthermore, the obtained correction filter has a low level of pre-ringing.

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  • ieee
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  • de-DE
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  • nn-NO
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  • asciidoc
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