A method and apparatus for outputting an audio signal and a method of adjusting the volume of an audio signal are provided. An embodiment of the present invention provides a method for outputting an audio signal that includes: (a) determining an output level of a modulated signal to be outputted for each respective frequency band by using a hearing threshold measured for the respective frequency band; and (b) outputting the modulated signal and an audio signal simultaneously. An embodiment of the present invention can improve hearing ability by outputting an audio signal and a modulated signal together. Also, according to an embodiment of the present invention, a user can use visual signals to personally set the output level of audio signals that is optimal for each frequency band in accordance with changes in the user's dynamic hearing threshold for each respective frequency band, even while listening to audio signals of which the output level for each frequency band was determined previously.