Hearing device comprising a delayless adaptive filter

A hearing device adapted to be worn by a user, or for being partially implanted in the head of the user, comprising

• a forward path for processing an audio signal, the forward path comprising
• at least one input transducer for converting a sound to a corresponding at least one electric input signal representing said sound,
• a hearing aid processor for providing a processed signal in dependence of said at least one electric input signal, or a signal originating there from, and
• an output transducer for providing stimuli perceivable as sound to the user in dependence of said processed signal,
• a feedback control system comprising
• an adaptive filter, and
• a combination unit,
• the adaptive filter comprising
• an adaptive algorithm unit, and
• a time domain time varying filter,
• wherein the adaptive algorithm unit is configured to provide a filter control signal for adaptively controlling filter coefficients of the time varying filter in dependence of different first and second algorithm input signals (e, u) of the forward path,
• the adaptive algorithm unit comprising
• first and second transform units for transforming said different first and second algorithm input signals (e, u) to respective first and second transform domain algorithm input signals (E, U),
• the adaptive algorithm being configured to provide an estimate (H′) in the transform domain of a current feedback path from the output transducer to the input transducer in dependence of said first and second transform domain algorithm input signals (E, U), wherein the adaptive algorithm is updated based on an unconstrained gradient determined from said first and second transform domain algorithm input signals (E, U) as U*⊙E, where * denotes the complex conjugate, and ⊙ denotes vector elementwise multiplication, and
• an inverse transform unit configured to convert the estimate of the current feedback path (H′) in the transform domain to an estimate of the current feedback path in the time domain (h′), and
• wherein said filter control signal is provided in dependence of said estimate of the current feedback path in the time domain (h′), and
• wherein the time domain time varying filter is configured to use adaptive filter coefficients controlled in dependence of said filter control signal to provide an estimate of an impulse response of the current feedback path (h) to thereby provide an estimate (v′) of a current feedback signal (v) in dependence of the processed signal (u), and
• the combination unit being located in the forward path and configured to subtract said estimate of the current feedback signal (v′) from a signal (y) of the forward path to provide a feedback corrected signal (e), and
• wherein said first and second transform units and said inverse transform unit comprise respective linear convolution constraints.