Method and apparatus for decoding input signal which encoding multi-channel to mono or stereo signal to 2 channel binaural signal

A method and an apparatus for decoding an input signal, that a multi-channel signal is compressed as a mono or stereo signal, into a binaural signal of 2 channels are provided to simplify an operating process by synthesizing and outputting the multi-channel signal as the binaural signal of the 2 channels without a process for recovering the input signal, that the multi-channel signal is compressed as the mono or stereo signal, is recovered as the multi-channel signal in a QMF(Quadrature Mirror Filter) domain. A channel level analyzing unit(204) calculates an FBCLs(Full Band Channel Levels) of respective channels composing a multi-channel from the CLD(Channel Level Difference) of the multi-channel. A two-channel synthesizing unit(208) performs the sound image localization of channel-classified data included in an input signal in directions corresponding to the channels on the basis of the calculated FBCLs of the respective channels.