Algorithms for active noise cancellation without exact knowledge of the error-path filter

The existence of a filter in the error path as in the case of active noise control has been shown to generally degrade the performance of the LMS algorithm. Thus the convergence rate is lowered, the residual power is increased and the algorithm can even become unstable. In order to stabilise the algorithm the input u(n) is filtered by a estimation of the error path filter leading to the FXLMS-algorithm. Modification of the FXLMS-algorithm assuring the well known properties of the LMS-algorithm by correcting the filtered error have also been reported. This correction of the filtered error also makes it possible to use RLS type algorithms for active noise cancellation. Common to all of the above cited algorithms is the need of a good estimate of the error-path filter. In this paper some possible alternatives that can do with very little knowledge of the error-path filter are analysed using a state space approach