5 A Practical Audio Acquisition System Using a Robust GSC (RGSC)

Abstract

In the preceding chapter, we have seen that data-dependent beamformers can be efficiently realized in GSC structures. However, GSCs, or more general LCLSE/LCMV beamformers, are sensitive to steering errors, to array perturbations and to reverberation w.r.t. the desired signal. Therefore, the performance of LCLSE/LCMV beamformers may decrease in realistic implementations: The desired signal may be distorted, a nd/or interference rejection may be reduced. In order to overcome these problems and to fully profit from the advantages of the GSC, we derive in this chapter a robust version of the GSC (RGSC). The problems of LCLSE/LCMV beamformers are resolved by using time-varying spatio-temporal constraints instead of purely spatial constraints [HK02a, HK03]. In contrast to spatial constraints, these s patiotemporal constraints explicitly take multi-pat h propagation w.r.t. the desired source into account by modeling the propagation by room impulse responses, such that the direct signal path and the secondary signal paths are cancelled at the output of the blocking matrix of the RGSC. Therefore, the RGSC is robust against cancellation of the desired signal in reverberant acoustic environments. In Chap. 2, it was shown that not only the propagation in a reflective environment can be modeled by impulse responses, but that n on-perfect transducer characteristics, i.e., directional-dependent and time-varying tolerances of the complex gain of the transducers, can be captured in impulse responses, too. Therefore, the RGSC is robust against tolerances of the characteristics or positions of the transducers without requiring explicit calibration. Timevarying spatio-temporal constraints take into account the temporal variations of the impulse responses between the desired source and the sensor signals due to speaker movements, changes in the acoustic environment, or time-varying complex gains of the sensors.