Stereo extension apparatus and method

A stereo extension apparatus comprising:

• a database that stores predetermined information as a result of Gaussian mixture model (GMM) training or hidden Markov model (HMM) training;
• a modified discrete cosine transform (MDCT) transformer that transforms a mono signal through MDCT;
• a feature parameter extractor that extracts a feature parameter of the mono signal from an MDCT coefficient output from the MDCT transformer;
• a side signal energy estimator that estimates subband energy of a side signal with reference to information stored in the database based on the feature parameter;
• an energy controller that obtains the MDCT coefficient of a side signal estimated from the subband energy of the estimated side signal;
• an inverse MDCT transformer that obtains an estimated side signal by transforming the MDCT coefficient of the estimated side signal through inverse MDCT;
• and
• a stereo signal generator that obtains a stereo signal based on sum and difference between the mono signal and the estimated side signal.