A method of processing an audio signal is disclosed. The present invention includes receiving, by an audio processing apparatus, an input signal; extracting a low frequency signal, a mid frequency signal and a high frequency signal from the input signal; obtaining at least one of a low-band gain and a harmonic control factor, based on a loudspeaker characteristic; obtaining mid-band gain based on the loudspeaker characteristic; generating a modified low frequency signal by applying the low-band gain to the low frequency signal; when the harmonic control factor is obtained, generating a harmonic signal from the modified low frequency signal using the harmonic control factor, generating a modified mid frequency signal by applying the mid-band gain to the mid frequency signal; and, generating a mixed signal by mixing the modified mid frequency signal, the high frequency signal, and at least one of the modified low frequency signal and the harmonic signal.