A method for decoding a signal, wherein the method comprises: obtaining spectral coefficients of sub-bands from a received bitstream by means of decoding; classifying sub-bands in which the spectral coefficients are located into a sub-band with saturated bit allocation and a sub-band with unsaturated bit allocation; performing noise filling on a spectral coefficient that has not been obtained by means of decoding and is in the sub-band with unsaturated bit allocation, so as to reconstruct the spectral coefficient that has not been obtained by means of decoding; and obtaining a frequency domain signal according to the spectral coefficients obtained by means of decoding and the reconstructed spectral coefficient; wherein the classifying sub-bands in which the spectral coefficients are located into a sub-band with saturated bit allocation and a sub-band with unsaturated bit allocation comprises: comparing an average quantity of allocated bits per spectral coefficient with a first threshold, wherein an average quantity of allocated bits per spectral coefficient of one sub-band is a ratio of a quantity of bits allocated for the one sub-band to a quantity of spectral coefficients in the one sub-band; and using a sub-band whose average quantity of allocated bits per spectral coefficient is not less than the first threshold as a sub-band with saturated bit allocation, and using a sub-band whose average quantity of allocated bits per spectral coefficient is less than the first threshold as a sub-band with unsaturated bit allocation; wherein the sub-band with unsaturated bit allocation refers to a sub-band in which allocated bits can be used to encode only a part of spectral coefficients in the sub-band, and a sub-band for which no bit is allocated. obtaining spectral coefficients of sub-bands from a received bitstream by means of decoding; classifying sub-bands in which the spectral coefficients are located into a sub-band with saturated bit allocation and a sub-band with unsaturated bit allocation; performing noise filling on a spectral coefficient that has not been obtained by means of decoding and is in the sub-band with unsaturated bit allocation, so as to reconstruct the spectral coefficient that has not been obtained by means of decoding; and obtaining a frequency domain signal according to the spectral coefficients obtained by means of decoding and the reconstructed spectral coefficient; wherein the classifying sub-bands in which the spectral coefficients are located into a sub-band with saturated bit allocation and a sub-band with unsaturated bit allocation comprises: comparing an average quantity of allocated bits per spectral coefficient with a first threshold, wherein an average quantity of allocated bits per spectral coefficient of one sub-band is a ratio of a quantity of bits allocated for the one sub-band to a quantity of spectral coefficients in the one sub-band; and using a sub-band whose average quantity of allocated bits per spectral coefficient is not less than the first threshold as a sub-band with saturated bit allocation, and using a sub-band whose average quantity of allocated bits per spectral coefficient is less than the first threshold as a sub-band with unsaturated bit allocation; wherein the sub-band with unsaturated bit allocation refers to a sub-band in which allocated bits can be used to encode only a part of spectral coefficients in the sub-band, and a sub-band for which no bit is allocated. comparing an average quantity of allocated bits per spectral coefficient with a first threshold, wherein an average quantity of allocated bits per spectral coefficient of one sub-band is a ratio of a quantity of bits allocated for the one sub-band to a quantity of spectral coefficients in the one sub-band; and using a sub-band whose average quantity of allocated bits per spectral coefficient is not less than the first threshold as a sub-band with saturated bit allocation, and using a sub-band whose average quantity of allocated bits per spectral coefficient is less than the first threshold as a sub-band with unsaturated bit allocation; wherein the sub-band with unsaturated bit allocation refers to a sub-band in which allocated bits can be used to encode only a part of spectral coefficients in the sub-band, and a sub-band for which no bit is allocated.