A filter apparatus for reducing noise from a primary noise source, comprising a secondary source signal connector for generating secondary noise to reduce said primary noise and a sensor connector for connecting to a sensor for measuring said primary and secondary noise as an error signal. A first control filter is arranged to receive a reference signal and calculate a control signal for the secondary source signal. A second control filter is arranged to receive a delayed reference signal and calculate an auxiliary control signal； wherein an adaptation circuit is arranged to adapt said second control filter while receiving an error signal as a sum of the auxiliary control signal and an auxiliary noise signal. The auxiliary noise signal is constructed from a difference of the delayed filtered error signal and a delayed control signal. The first control filter is updated by a copy of said updated second control filter.
