Patent ID: 7636660

Claim:
A subband synthesis filtering apparatus for M sets of signals which each comprises N subband sample signals, M and N being both positive integers, said apparatus comprising: 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 comprising: a discrete cosine transform (DCT) module for converting the N subband sample signals of the ith set of signals into N converted vectors based on a DCT, wherein 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 DCT module, wherein j is an integer index ranging from 1 to (N/2); and a generating module for generating N pulse code modulation (PCM) signals based on the N converted vectors; wherein the M sets of signals are in accordance with the MPEG-1 Layer III standard; M is equal to 18, and N is equal to 32, the kth subband sample signal among the 32 subband sample signals of the ith set of signals is represented as x(k−1); k is an integer index ranging from 1 to 32, and the DCT module processes x(p), x( 31 −p), x( 15 −p), and x( 16 +p), wherein p is an integer index ranging from 0 to 7, and the DCT module judges whether i is an odd number, if the judging result is NO, the DCT module calculates four intermediate results (g1(p), g2(p), g3(p), and g4(p)) corresponding to p based on a first set of equations; if the judging result is YES, the DCT module judges whether p is an odd number and then selectively calculates the four intermediate results (g1(p), g2(p), g3(p), and g4(p)) corresponding to p via a second set of equations or a third set of equations according to the judging result about whether p is an odd numbers.