Effects of secondary path modeling errors on the Modified FX-LMS algorithm for Active Noise Control

The Modified FX-LMS (MFX-LMS) algorithm has been the subject of some research. It effectively removes the delay from the adaptation mechanism allowing faster convergence rates than the FX-LMS. It also allows the use of more sophisticated algorithms such as the RLS or the Kalman. Although this is true for perfect secondary path modeling, there is no extensive study of the influence of secondary path modeling errors in this algorithm. This paper tries to do just that. It shows that it's maximum allowed step-size is in fact almost independent of the delay in the secondary path, even in the presence of modeling errors. It also shows that for very large delays the algorithm is stable for phase errors of +/-60degrees and for an estimated amplitude of more than half of the correct one.