Method and audio processing system determine a system parameter sp in a gain loop of an audio processing system. An alternative scheme is provided for feedback estimation in a multi-microphone audio processing system comprising an injected probe signal. The problem is solved in that a) an expression of an approximation of the expected square of the stationary loop gain, LGstat(ω,n), and b) an expression of the convergence or decay rate of the expected square of the stationary loop gain, LGstat(ω,n), after an abrupt change in one or more system parameters are determined, and in that c) a system parameter sp is determined from one of said expressions under the assumption that other system parameters are fixed. The method has the advantage of providing a relatively simple way of identifying and controlling dynamic changes in the acoustic feedback path(s).