Method and apparatus for bandwidth extension decoding

PURPOSE: A bandwidth extension decoding method and a device thereof are provided to decode a high frequency signal by using a spectrum or a residual signal about a low frequency signal coded in a frequency area or a time area. CONSTITUTION: When a low frequency signal corresponding to a smaller area than a predetermined frequency is decoded in a time area, the signal is decoded and converted into a frequency area (310). When the low frequency signal is decoded into the frequency area, a residual spectrum is decoded (320). A spectrum is generated in a predetermined bigger area by using the decoded residual spectrum or the spectrum of the residual area which is converted (325). The decoded information is applied to the generated spectrum by decoding information related to energy of the signal (335). [Reference numerals] (300) Demultiplex; (305) Has a low frequency signal been encoded in a time domain ?; (310) Decode the low frequency signal and an excitation signal in the time domain; (315) Create the excitation signal's spectrum for the low frequency signal; (320) Decode the low frequency signal and the excitation spectrum in a frequency domain; (325) Generate an excitation spectrum in a high frequency domain; (330) Decode a gain value; (335) Apply the gain value to the spectrum; (340) Add a noise to the spectrum; (345) Convert the spectrum into the time domain; (350) Compose the low frequency signal with the high frequency signal; (AA) Start; (BB) No; (CC) Yes; (DD) End