Some Contributions to Adaptive Filtering for Acoustic Multiple-Input/Multiple-Output Systems in the Wave Domain


Publication Details

Author(s): Schneider M
Publisher: Verlag Dr. Hut
Publishing place: Munic, Germany
Publication year: 2016
ISBN: 9783843926690
Language: English


Recently emerging techniques like wave field synthesis (WFS) or Higher-Order Ambisonics (HOA) allow for high-quality spatial audio reproduction, which makes them candidates for the audio reproduction in future telepresence systems or interactive gaming environments with acoustic human-machine interfaces. In such scenarios, acoustic echo cancellation (AEC) will generally be necessary to remove the loudspeaker echoes in the recorded microphone signals before further processing. Moreover, the reproduction quality of WFS or HOA can be improved by adaptive pre-equalization of the loudspeaker signals, as facilitated by listening room equalization (LRE). However, AEC and LRE require adaptive filters, where the large number of reproduction channels of WFS and HOA imply major computational and algorithmic challenges for the implementation of adaptive filters. A technique called wave-domain adaptive filtering (WDAF) promises to master these challenges. However, known literature is still far away from providing sufficient insight to allow for a successful implementation of real-world systems.

This thesis is concerned with the further development of WDAF-based generic signal processing algorithms and acoustic models aiming at real-time, real-world implementations of AEC and LRE.
As prototypical scenario, an exemplary loudspeaker and microphone setup is considered for which the necessary wave-domain transforms are explicitly derived and analyzed. Thereby, the origins of the desirable wave-domain properties of the loudspeaker-enclosure-microphone system (LEMS) are explained.

For both, AEC and LRE, it is necessary to identify an LEMS, while the computational demands of this task render a real-time implementation unrealistic, if a large number of reproduction channels should be considered without approximative models. The originally proposed approximative wave-domain LEMS model is generalized such that the number of degrees of freedom can be chosen to provide the maximum model accuracy given the applicable computational restrictions. Typical reproduction signals will often not allow to find a unique solution to the system identification problem for multichannel reproduction. A novel, rigorous and in-depth analysis of this so-called nonuniqueness problem is conducted in this thesis. Furthermore, a wave-domain technique to improve the system identification when nonuniqueness occurs is presented. This technique does not influence the reproduced signals, as it would be the case for other known state-of-the-art solutions.

For an implementation of adaptive filters in the wave domain, modified versions of well-known adaptation algorithms are derived, considering approximative models and improving system identification. The modified algorithms are based on the least mean squares (LMS) algorithm, the affine projection algorithm (APA), the recursive least squares (RLS) algorithm, or the generalized frequency-domain adaptive filtering (GFDAF) algorithm, which is identified as an approximation of the RLS algorithm. Additionally, a novel iterative algorithm for the determination of equalizers is presented. Experimental results support the claim of applicability of the considered approach. Moreover, a real-time wave-domain AEC demonstrator has been developed which facilitates AEC for 48 loudspeaker channels on a conventional personal computer.

On the other hand, the equalizer determination necessary for LRE is an inverse system identification problem. It is shown that the nonuniqueness problem occurs also for this task while the properties of the LEMS can additionally cause nonuniqueness. In this thesis, a generalized wave-domain approximative equalizer structure is successfully applied, which potentially allows for a real-time implementation of LRE. The achievable LRE performance with an approximative wave-domain system is assessed by simulations.

Decisive problems for the real-word implementation could be solved or mitigated using results presented in this thesis. Nevertheless, other challenging research questions remain unanswered and will fuel future research in this area.

FAU Authors / FAU Editors

Schneider, Martin
Lehrstuhl für Multimediakommunikation und Signalverarbeitung

How to cite

Schneider, M. (2016). Some Contributions to Adaptive Filtering for Acoustic Multiple-Input/Multiple-Output Systems in the Wave Domain (Dissertation).

Schneider, Martin. Some Contributions to Adaptive Filtering for Acoustic Multiple-Input/Multiple-Output Systems in the Wave Domain. Dissertation, Munic, Germany: Verlag Dr. Hut, 2016.


Last updated on 2019-19-04 at 13:07