Subband merging in cosine-modulated filter banks

Recently, a new method for constructing nonuniform modulated lapped transforms (MLTs) was introduced, by combining subband filters of a uniform MLT. The design, however, was restricted to combining two or four subband filters only, and no systematic design procedure was given. In this letter, we propose an extension to the above-mentioned method that allows arbitrary numbers of subbands to be combined in a systematic way. We investigate the general case of combining filters in arbitrary cosine-modulated filter banks, and give conditions on how to combine the constituent filters such that the resulting nonuniform filter banks have suitable frequency responses.