A modified perfect reconstruction QMF bank with an auxiliary channel

Quadrature mirror filter (QMF) banks have been studied extensively because of their attractive properties, which are useful in many applications. One desirable property is perfect reconstruction, i.e. in the absence of any channel modifications the filter bank transfer function should be a pure delay. The process of designing filter banks having this perfect reconstruction property is not easy due to the restrictions imposed on the filters. In addition, in some applications such as adaptive filtering, there are problems with using QMF banks due to the aliasing introduced in the output. This is the motivation for developing the modified filter bank structure presented in this paper, which has in addition to the main decimated nonoverlapping subbands a narrowband auxiliary channel that is not decimated. This structure offers advantages in ease and flexibility of design, and it is shown to have a computational complexity comparable to that of conventional QMF banks. Applications in adaptive filtering and subband coding are mentioned.>