Abstract: The acoustical-mechanical disturbance feedback between the electrical-acoustical converter and the acoustical-electrical converter of a hearing aid apparatus is compensated by means of an adaptive compensator filter which feeds back a signal derived from the output of an amplification filter to its input. At the input side thereby the signal from the acoustical-to-electrical converter and the output signal of the adaptive compensator filter are substracted at a difference forming unit, the output of which being led to the input of the amplification filter. The difference is thereby formed in time domain, and time domain to frequency domain transform is performed at the output side of the difference forming unit, accordingly inverse frequency domain to time domain transform at the electric input side of the electrical-to-acoustical converter.