Modulated filter banks: A folding approach

Cosine Modulated Filter Banks (MFB) have been widely studied [MAL92, KOI92, MAU94] and are successfully used in signal and image processing. A perfect reconstruction factorization of filter banks based on cosine modulation of a linear phase prototype filter of length L=2KM has been proposed in [MAL92, KOI92]. This factorization leads to paraunitary MFB where the analysis and synthesis filters are the same. In this paper, we generalize the folding operator introduced in [AUC92]. That permits the extension of the factorization to the L=NM case, with a more general modulation matrix. If N is even, the MFB is either paraunitary or biorthogonal. While if N is odd, the MFB is biorthogonal.