The present invention provides a feedback system including a mixing circuit, a forward circuit, a feedback circuit, a feedback gain circuit and a control circuit. In the operations of the feedback system, the mixing circuit generates a mixed signal according to an input signal and a feedback signal, the forward circuit processes the mixed signal to generate an output signal, the feedback gain circuit and the feedback circuit generates the feedback signal according to the output signal, and the control circuit determines a feedback gain of the feedback gain circuit according to a gain of the forward circuit.