1. A method for decoding an audio signal, the method comprising: receiving, by an audio processing apparatus, spectral data including a current block having a spectral hole, and substitution type information indicating whether to apply a shape prediction scheme to the current block, based on the substitution type information indicating that the shape prediction scheme is applied to the current block, receiving lag information indicating an interval between spectral coefficients of the current block and a predictive shape vector of the shape prediction scheme, and wherein the substitution type information is determined based on a correlation value between spectral coefficients of the current block and the predictive shape vector, the correlation value is estimated by using a candidate lag value (d k ), and based on the correlation value being greater than or equal to a predetermined value, the shape prediction scheme is applied to the current block having the spectral hole; obtaining spectral coefficients by substituting for spectral hole included in the current block using the lag information; and decoding the spectral coefficients to output the audio signal.