A apparatus and method extending bandwidth of sound signal

In bandwidth extension unit of the sound signal in accordance with the present invention, GMM and HMM Training Training training at least one predetermined information is stored in the database in accordance with the; Claim 1 MDCT converter for the band changing signal MDCT; Feature extraction unit for extracting a feature value of the first band signal from the MDCT coefficient outputted from the MDCT converter; Expansion unit for providing an extended MDCT coefficients for the second band signal from the MDCT coefficient of the first band signal outputted from the MDCT converter; The Based on the feature value referring to the information stored in the database, a sub-band energy estimator for estimating the second-band signals sub-band energy; Part 2 band signal generation to provide an MDCT coefficient of the second and extended MDCT coefficient for a band signal, the second signal band estimated by using the sub-band energy of the second band signal is estimated; The estimated first inverse MDCT transform for converting the MDCT coefficient inverse MDCT of the second band signals to provide an estimated second-band signals; The estimating portion includes the second band signal with said first composite signal by combining the band obtain a third band signal. According to the present invention, it is possible to implement a high-quality call service with no additional bit in the Internet communication network degradation, especially, it is possible to implement a high-quality call service, even when the movement of the terminal frequently, such as wireless Internet.