| 1. |
- Bahne, Adrian, et al.
(författare)
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Improved loudspeaker-room equalization for stereo systems regarding channel similarity
- 2012
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Ingår i: Proceedings - International Conference on Audio, Language and Image Processing. - 9781467301718 ; , s. 254-259
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 2. |
- Bahne, Adrian, 1983-
(författare)
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Multichannel Audio Signal Processing : Room Correction and Sound Perception
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns and combines multichannel sound reproduction, digital room correction, audio signal processing, and human sound perception. It investigates perceived sound quality and new methods to improve timbral and spatial fidelity of loudspeaker-based multichannel sound reproduction in reverberant environments.In the first part of the thesis, the perceived sound quality of regular optimized stereo sound systems is investigated by means of a listening experiment based on subjective comparison judgments. It is shown that average listeners' preferences are in favor of the optimized version of the systems.The second part of the thesis takes on with three novel equalization schemes, which are based on insights from human perception. First, a general filter design framework based on multiple-input multiple-output (MIMO) feedforward control is introduced. The main objective is to provide means to jointly equalize a single loudspeaker by utilizing all available loudspeakers in a multichannel sound system.Well-known drawbacks of standard multichannel sound reproduction are (a) that symmetrical system setups are generally assumed, and (b) that high fidelity sound reproduction is limited to a tight region in space, the so-called sweet spot. In order to ease drawback (a), the MIMO similarity framework incorporating a pairwise channel similarity requirement is introduced, which is based on a mathematical description of the perception of virtual sound sources created in multichannel sound reproduction. The aim is to obtain similar (symmetrical) room transfer functions in the listening area of a given listening environment. In order to ease drawbacks (a) and (b), the personal audio framework is introduced. It aims at producing filters which improve spatial and timbral sound reproduction in multiple listening positions simultaneously.Evaluations based on simulations and measurements acquired in representative listening environments strongly indicate that the proposed methods successfully treat several causes which are known to impair sound quality and thus yield improved sound reproduction.
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| 3. |
- Bahne, Adrian, et al.
(författare)
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Symmetric loudspeaker-room equalization utilizing a pairwise channel similarity criterion
- 2013
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Ingår i: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 61:24, s. 6276-6290
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Barkefors, Annea, et al.
(författare)
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Design and Analysis of Linear Quadratic Gaussian Feedforward Controllers for Active Noise Control
- 2014
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Ingår i: IEEE Transactions on Audio, Speech, and Language Processing. - 1558-7916 .- 1558-7924. ; 22:12, s. 1777-1791
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Barkefors, Annea
(författare)
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Linear Quadratic Gaussian Controllers for Feedforward Active Noise Control : Pushing Performance and Moving Towards Adaptive Control
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Active noise control is a research area focused on using destructive interference of sound fields to attenuate undesired noise. Methods for active noise control are best suited for low frequency noise, as the complexity of the problem grows rapidly with frequency. Coincidentally, passive means of damping have the opposite quality in that they work better for higher frequencies and become bulky and impractical for low frequencies. Applications for active noise control range from fan noise in ducts, noise-cancelling headphones and noise in cars to propeller induced aircraft cabin noise. In this comprehensive summary, the underlying principles of active noise control are presented and the control problem is discussed. Several aspects of the control system are introduced to give an introduction to the research papers that are the basis of this licentiate thesis. The work behind the thesis is focused on a Multiple-Input Multiple-Output (MIMO) Minimal Mean Square Error (MMSE) Linear Quadratic Gaussian (LQG) feedforward controller. This controller is shown to achieve uniform damping in an extended region in space and push the upper frequency that can be controlled. The influence of different design variables has been investigated, and the properties of the control path analyzed with consideration of its ability to suppress noise of prescribed spectral properties over an extended region. In this context, it has been shown how to use the reproducibility of the primary noise path by the control path as an indication of achievable performance for a given control system. Finally, the controller has been adapted to follow changes in the primary noise statistics, an approach that seems promising to considerably raise the performance of the controller.
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| 6. |
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| 7. |
- Brännmark, Johan, et al.
(författare)
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Ethical theory and the philosophy of risk: first thoughts
- 2010
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Ingår i: Journal of Risk Research. - : Informa UK Limited. - 1366-9877 .- 1466-4461. ; 13:2, s. 149-161
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Tidskriftsartikel (refereegranskat)abstract
- Contemporary psychological research has shown that if we are judged by the standards of classical models of rationality our decision-making abilities can be seriously questioned. We are more or less irrational. The article investigates how this 'fact of irrationality' affects the way normative ethical theories should be formulated and the extent to which currently dominant ethical theories can be taken seriously as normative ideals of actual human decision-making. It is argued that these theories tend to presuppose a too unified and rationalistic account of human agency and that there is reason to turn attention instead to a level of ethical theorizing that lies between traditional ethical theory and applied ethics. It is also argued that given such an approach, matters of risk and uncertainty should be more directly integrated into basic ethical theorizing than what is traditionally the case.
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| 8. |
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| 9. |
- Brännmark, Lars-Johan, et al.
(författare)
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Compensation of Loudspeaker-Room Responses in a Robust MIMO Control Framework
- 2013
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Ingår i: IEEE Transactions on Audio, Speech, and Language Processing. - 1558-7916 .- 1558-7924. ; 21:6, s. 1201-1216
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Brännmark, Lars-Johan, et al.
(författare)
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Improved loudspeaker-room equalization using multiple loudspeakers and MIMO feedforward control
- 2012
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Ingår i: Acoustics, Speech and Signal Processing (ICASSP), 2012 IEEE International Conference. - 9781467300445 ; , s. 237-240
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Konferensbidrag (refereegranskat)abstract
- 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.
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