PURPOSE: To eliminate completely correlations among channels in the preprocessing of digital encoding of a multichannel signal such as a stereo signal or the like by adding a delay time to the multichannel input signal so that a coefficient of correlation among channels is maximum and converting the signal linearly so that no correlations exist among channels and the deflection of power is great and encoding the signal with the number of quantizing bits which is different in accordance with the magnitude of each power.

CONSTITUTION: The multichannel signal is inputted to a correlation function calculating part 2 and delay adding parts 3, and the calculating part 2 takes in N- number of samples of each channel and calculates a coefficient of correlation among channels. An orthogonal converting part 4 converts the multichannel signal given from the delay adding circuits 3 to a signal where no correlations exist among channels and the deflection of power is great. A converted signal Y(t) obtained in the orthogonal converting part 4 is given to encoders 5 and a bit assigning part 6, and power of the converted signal Y(t) is calculated to determine the number of encoded bits of each channel, and the signal is encoded with different numbers of bits.