Uppsala universitet

Spatially Robust Audio Compensation Based on SIMO Feedforward Control.

Lars-Johan Brännmark and Anders Ahlén,

IEEE Transactions on Signal Processing, vol. 57, no. 5, May 2009, pp. 1689-1702.

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 based 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.

Related publications:
PhD Thesis by Lars-Johan Brännmark

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