According to an embodiment, the above-described specification discloses an electronic device comprises at least one processor configured to: receive a first audio signal and a second audio signal; detect a spectral envelope signal from the first audio signal and extract a feature point from the second audio signal; extend a high-band of the second audio signal based on the spectral envelope signal from the first audio signal and the feature point from the second audio signal to generate a high-band extension signal; and mix the high-band extension signal and the first audio signal, thereby resulting in a synthesized signal.