A signal processing apparatus includes a signal generating block arranged to generate a target estimated signal of a specific signal component in an input signal. The signal generating block includes a reference signal generating circuit, a signal processing circuit, and a signal adjusting circuit. The reference signal generating circuit is arranged to generate a reference estimated signal for the specific signal component in the input signal. The signal processing circuit is coupled to the reference signal generating circuit, and arranged to process the reference estimated signal and accordingly generate a signal processing result. The signal adjusting circuit is coupled to the signal processing circuit and the reference signal generating circuit, and arranged to output the target estimated signal by adjusting the reference estimated signal according to the signal processing result.