The invention provides an apparatus that is adapted to adjust the amplitude of an audio signal based on the background. The apparatus, according to a preferred embodiment of the invention, includes an audio receiving module. The audio receiving module is adapted to receive a first audio and a second audio and to generate a process signal including a first signal and a second signal. A processing module extracts the second signal from the process signal. An adjusting module receives the extracted second signal and generates a gain in accordance with the extracted second signal and a criterion. The adjusting module adjusts the amplitude of the audio signal in accordance with the gain.