Method and apparatus for encoding and decoding signal

The present invention relates to a method and apparatus for encoding or decoding an audio signal, mixing (downmixing) down the signals of two or more channels into a mono signal in as encoding the audio signal and the mono signal, the low-frequency signal and a high-frequency divided into a signal, and a low-coding the frequency signal into an ACELP (Algebraic Code Excited Linear Prediction) or TCX (Transform coded excitation) and the low-and using the frequency signal, according as coding the frequency signal, and decodes an audio signal ACELP or the low-coded in TCX-decoding a frequency signal and a low-to synthesize the frequency signal to generate a monaural signal, and of two or more channel signals, and using a frequency signal, decode the frequency signal and the low-frequency signal and the high for decoding the spatial information (spatial parameter) and to the up mixer (upmixing) a mono signal.