Quadrature mirror filter

QMF filter banks. Quadrature mirror filters (QMF, see [Esteban and Galand, 1977]) have often been proposed for audio coding. The most common configuration is the tree of filters with a two-way split. In one of the early examples [Theile et al., 1987] the 64d filter design from [Johnston, 1980] has been used. The decomposition tree is set up so that the filter bands resemble critical bands. The QMF halfband filters are non-perfect reconstruction, but with perfect alias cancellation by design. The reconstruction error of the analysis/synthesis pair can be held at small amplitudes by increasing the filter length. 

Johnston, 1980] Johnston, J. D. (1980). A Filter Family Designed for Use in Quadrature Mirror Filter Banks. In Proc. IEEE Int. Conf. Acoust., Speech and Signal Proc, pages 291-294. 

Quadrature Mirror Filter (QMF) is a set of coefficients for transformation algorithms that act as a filter when applied to a raw data vector. 

PIRAMID system overview, CATHEDRAL-II, module generation, floorplanning, the EXUs designed, and a quadrature mirror filter example. 

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