Using phase information to decorrelate the filtered-x algorithm

A well known algorithm in the field of active noise control is the filtered-x algorithm. As known in the literature, the convergence properties of an adaptive algorithm can be improved by decorrelating its input signal. The decorrelation needed for the filtered-x algorithm is discussed with the help of block frequency domain adaptive filters. It is shown that decorrelation of not only the input signal but also the amplitude response of the secondary acoustic path is necessary. While the former can be done by dividing the input signal in the frequency domain by an estimate of the input signal power, the latter leads to a new method for improving convergence properties without any extra computation; by using only the phase information of the secondary path to calculate the filtered-x signal.