Low-delay subband adaptive filter

Abstract

A subband adaptive filter is disclosed that retains the computational and convergence speed advantages of subband processing while eliminating delay in the signal path. The technique has applications in active noise control where delay seriously limits cancellation performance and in acoustic echo cancellation where transmission delay specifications may limit the use of conventional subband designs. A reference signal and a residual error signal are each decomposed into a plurality of subband signals, and a set of adaptive weighting coefficients is generated for each of these subbands by a conventional complex LMS (least-mean-squared) technique. These sets of subband weighting coefficients are then transformed into the frequency domain, appropriately stacked and inverse transformed back into the time domain to obtain wideband filter coefficients for a programmable filter. The reference signal, which is correlated with the disturbance signal to be eliminated, is filtered by this programmable filter to produce a disturbance estimate signal which may be subtracted from the signal containing the disturbance. The process iterates in order to minimize the residual error signal and thereby reduce the disturbance.