Uppsala universitet


Signals and Systems, Uppsala University

Researchers: Anders Ahlén , Viktor Gunnarsson , and Mikael Sternad

Previous PhD students: Adrian Bahne , Annea Barkefors , Lars-Johan Brännmark and Simon Widmark .

Industrial collaboration partner: Dirac Research AB

Article (in Swedish) on some of our audio research in Ergo, May 16, 2012.

Invited Overview ISEAT conference, Shenzen, China, Nov. 2015.

Room Correction and Sound Field Control

We investigate the design and analysis of digital filters for various audio reproduction application:

  • Loudspeaker equalization and room correction, where the signal to a loudspeaker is filtered to improve the sound reproduction quality.
  • Multichannel design, where a sound field is to be reproduced by the joint use of multiple loudspeakers.
  • Analysis: How is the attainable performance affected by a given equipment, geometry and knowledge of the channels? How would the performance vary if we change the equipment and/or the geometry, or base the design on different prior knowledge?
The problems mostly constitute linear feedforward control problems, based on multiple measurements. We use very complicated high-order acoustic transfer functions that are partly unknown. To obtain new results, we utilize and further develop results on polynomial methods for linear control and filtering as well as on robust control and filtering.

Our research results have found applications in world-class high-end automotive audio systems, cinema audio processors and digitally optimized HiFi systems.

Psycho-acoustic Research

One characteristic of the design and analysis of audio signal processing system is that the ultimate criterion is not easily captured objectively: It constitutes a perceptual quality experienced by a listener, or a group of listeners. It is therefore crucial to investigate the perceptual results of various compensation and sound control schemes. Our aim is to better objectively characterize differences in subjective experience and to better capture the perceptual effect of different audio compensation schemes.

Active Noise Control and Personal Sound

In our research effort on active noise control, we investigate ways to use digital audio systems in cars and trucks also for active noise control: The bass loudspeakers of the sound system then produce anti-noise, which cancels low-frequency engine noise or road noise at the driver or passenger positions. This reduces the cost and complexity as compared to stand-alone solutions.

In this research we are using and extending previous results on controller design as well as on adaptive filtering.

Our research on active noise control is supported by the Swedish Research Council.


The Signals and Systems group has led the design and construction of an anechoic chamber, designed for both acoustic and radio-frequency measurements, at the Ångtröm Laboratory at Uppsala University. The chamber and measurement equipment was funded by the Knut and Alice Wallenberg Foundation. The chamber was finalized in 2009 and has a size of (LxWxH) 11.9 x 9.6 x 6.1 m. It constitutes a well damped environment in which experiments can be performed for the purpose of evaluating the effectiveness of different algorithms.

The audio equipment consists of sixteen active ATC loudspeakers, eight DPA microphones and two Prism Orpheus sound cards having in total eight inputs and sixteen outputs. The chamber, together with the equipment, thus constitutes an excellent testbed for conducting controlled acoustic experiments.

[Measurement chamber at the Ångström Laboratory]

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Academic Theses:

PhD Thesis by Simon Widmark, on causal MMSE filters for personal audio.

PhD Thesis by Adrian Bahne, on multichannel audio signal processing.

Licentiate Thesis by Annea Barkefors, on LQG feedforward active noise control.

PhD Thesis by Lars-Johan Brännmark, on robust sound field control.

Selected References: Journal Papers

Paper in IEEE TASLP 2019 on causal MSE-optimal filters for personal audio subject to contrast constraints.

Paper in IEEE TASLP 2018 on causal IIR audio precompensator filters subject to quadratic constraints.

Paper in IEEE TASLP 2016 on optimizing the similarity of loudspeaker-room responses in multiple listening positions.

Journal AES 2015 on multichannel room correction with focus control.

Paper in IEEE TASLP 2014, Design and analysis of Linear Quadratic Gaussian feedforward controllers for active noise control.

Paper in IEEE SP 2013 on symmetric loudspeaker-room equalization utilizing a pairwise channel similarity criterion.

Paper in IEEE TASLP 2013 on compensation of loudspeaker-room responses in a robust MIMO control framework.

Journal AES 2012 on perceived sound quality of small original and optimized loudspeaker systems.

Paper in IEEE SP 2009 on spatially robust audio compensation based on SIMO feedforward control.

Paper in JASA 2009 on multiple-point statistical room correction.