On the Subband Orthogonality of Cosine-Modulated Filter Banks

In this brief, the second-order characteristics of cosine-modulated filter banks are formulated and analyzed. We show that, for any type of input spectrum, adjacent subband signals of a cosine-modulated filter bank are properly phase-aligned in such a way that they are nearly orthogonal at zero lag even though they are not mutually exclusive. The orthogonal properties are desirable in reducing the computational complexity of subband processing systems.