An apparatus for decoding a signal, comprises: at least one processor; and a memory storing computer executable instructions for execution by the at least one processor, wherein the computer executable instructions instruct the at least one processor to obtain spectral coefficients of sub-bands from a received bitstream by means of decoding; classify 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; perform 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 obtain a frequency domain signal according to the spectral coefficients obtained by means of decoding and the reconstructed spectral coefficient; wherein the computer executable instructions further instruct the at least one processor to: compare 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 use a sub-band whose average quantity of allocated bits per spectral coefficient is greater than or equal to 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. at least one processor; and a memory storing computer executable instructions for execution by the at least one processor, wherein the computer executable instructions instruct the at least one processor to obtain spectral coefficients of sub-bands from a received bitstream by means of decoding; classify 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; perform 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 obtain a frequency domain signal according to the spectral coefficients obtained by means of decoding and the reconstructed spectral coefficient; wherein the computer executable instructions further instruct the at least one processor to: compare 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 use a sub-band whose average quantity of allocated bits per spectral coefficient is greater than or equal to 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. compare 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 use a sub-band whose average quantity of allocated bits per spectral coefficient is greater than or equal to 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.