METHOD AND APPARATUS OF POSTFILTERING USING A FIRST SPECTRUM PARAMETER OF AN ENCODED SOUND SIGNAL AND A SECOND SPECTRUM PARAMETER OF A LESSER DEGREE THAN THE FIRST SPECTRUM PARAMETER

A second spectrum parameter of which degree is lower than that of a first spectrum parameter is calculated based on the first spectrum parameter that is output from an encoder. A spectrum postfilter generates a transfer function having a denominator and a numerator wherein said first spectrum parameter is included in said denominator and said second spectrum parameter is included in said numerator, and filters the reduced signal with this transfer function. In addition, it adaptively generates a compensation coefficient based on the first and second parameters. A compensation filter generates a transfer function based the compensation coefficient and filters an output of the spectrum postfilter with this transfer function.