A signal processing system and method is disclosed, applicable to environment providing voltage to Class-H driver. When using the signal processing system, the first is to detect the volume change of inputted voice and use the detection result as a power source to generate an expectation value for the circuit; the input end of the power generation circuit also adds a voltage offset in addition to the expectation value, so that the output voltage from the output end of the power generator provided to the Class-H driver is higher than a fixed value. The signal processing system and method of the present invention can adjust automatically and rapidly the output voltage signal for the power voltage provided to the Class-H driver by using negative feedback controller (such as, negative feedback loop, voltage offset and proportional integral differential (PID)) based on the detected volume change of inputted voice.