A method of processing an audio signal, comprising: extracting spatial information, a narrow-band downmix signal (DMX n) corresponding to a first band and band extension information from a bitstream; decoding the narrow-band downmix signal using an audio coding scheme, if the narrowband downmix signal has more audio characteristic; decoding the narrow-band downmix signal using a speech coding scheme, if the narrowband downmix signal has more speech characteristic, wherein the speech coding scheme includes Linear Prediction Coding, LPC; extracting start band information, gain information and harmonic component information from the band extension information; receiving spectral data corresponding to the first band in a frequency band from the narrow-band downmix signal; determining a copy band based on frequency information of the copy band corresponding to a partial band of the first band; generating spectral data of a target band by applying the gain information to the spectral data of the copy band and by further using the harmonic component information; and generating a multi-channel output signal using a broadband downmix signal (DMX w) and the spatial information, wherein the broadband downmix signal includes the spectral data of the target band and the spectral data of the first band, wherein: the spectral data of the target band is generated by a combination of a time dilatation step and a decimation step, the time dilatation step being for dilating a time domain signal using a phase vocoder scheme, the copy band exists in an upper part of the first band, the spectral data of the first band is generated based on the narrowband downmix signal decoded by either the audio coding scheme or the speech coding scheme, the frequency information of the copy band comprises at least one of a start frequency, a start band, and index information indicating the start band, wherein, if the copy band is different from the start band, the copy band is determined as a band from a band corresponding to the start band information to a band having the spectral data, and the spectral data of the target band is generated using at least one of gain information corresponding to a gain between the spectral data of the copy band and the target band, and the harmonic component information of the copy band. extracting spatial information, a narrow-band downmix signal (DMX n) corresponding to a first band and band extension information from a bitstream; decoding the narrow-band downmix signal using an audio coding scheme, if the narrowband downmix signal has more audio characteristic; decoding the narrow-band downmix signal using a speech coding scheme, if the narrowband downmix signal has more speech characteristic, wherein the speech coding scheme includes Linear Prediction Coding, LPC; extracting start band information, gain information and harmonic component information from the band extension information; receiving spectral data corresponding to the first band in a frequency band from the narrow-band downmix signal; determining a copy band based on frequency information of the copy band corresponding to a partial band of the first band; generating spectral data of a target band by applying the gain information to the spectral data of the copy band and by further using the harmonic component information; and generating a multi-channel output signal using a broadband downmix signal (DMX w) and the spatial information, wherein the broadband downmix signal includes the spectral data of the target band and the spectral data of the first band, the spectral data of the target band is generated by a combination of a time dilatation step and a decimation step, the time dilatation step being for dilating a time domain signal using a phase vocoder scheme, the copy band exists in an upper part of the first band, the spectral data of the first band is generated based on the narrowband downmix signal decoded by either the audio coding scheme or the speech coding scheme, the frequency information of the copy band comprises at least one of a start frequency, a start band, and index information indicating the start band, wherein, if the copy band is different from the start band, the copy band is determined as a band from a band corresponding to the start band information to a band having the spectral data, and the spectral data of the target band is generated using at least one of gain information corresponding to a gain between the spectral data of the copy band and the target band, and the harmonic component information of the copy band.