A subband synthesis filtering apparatus for M sets of signals is provided. Each set of signals includes N subband sample signals. The apparatus includes a processor for processing the ith set of signals among the M sets of signals, wherein i is an integer index ranging from 0 to (M−1). The processor includes a DCT converting module and a generating module. The DCT converting module converts the N subband sample signals of the ith set of signals into N converted vectors. If i is an odd number, the (2j−1)th subband sample signal among the N subband sample signals is multiplied by negative one in the converting module, whereinj is an integer index ranging from 1 to (N/2). The generating module generates N pulse code modulation signals based on the N converted vectors.