An apparatus and method for keeping output loudness and quality of sound in different equalizer modes. The apparatus includes a gain setting unit configured to set a protection limit of an output voltage of an input audio signal; an equalizer (EQ) mode filter configured to filter the input audio signal so as to achieve the different equalizer modes; an amplitude real-time processing module configured to receive the audio signal output from the EQ mode filter or an audio signal feedback, and process the received audio signal such that the output voltage of the processed audio signal is lower than the protection limit; and a digital-to-analog converter configured to perform a digital-to-analog conversion on the processed audio signal, and output an analog audio signal.