An apparatus for processing an audio signal and method thereof are disclosed. The present invention includes receiving a spectral data of lower band and type information indicating a particular band extension scheme for a current frame of the audio signal from among a plurality of band extension schemes including a first band extension scheme and a second band extension scheme, by an audio processing apparatus; when the type information indicates the first band extension scheme for the current frame, generating a spectral data of higher band in the current frame using the spectral data of lower band by performing the first band extension scheme; and when the type information indicates the second band extension scheme for the current frame, generating the spectral data of higher band in the current frame using the spectral data of lower band by performing the second band extension scheme, wherein the first band extension scheme is based on a first data area of the spectral data of lower band, and wherein the second band extension scheme is based on a second data area of the spectral data of lower band.