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Abstract

The invention relates to a digital filter tree composed of a plurality of digital filter banks arranged in a tree structure one behind the other to branch out in stages with a separation into L.sub..nu. individual signals taking place in each stage and the sampling rate being reduced each time by the factor M.sub..nu. where .nu.=1,2, . . . identifies the .nu.th stage. The filter tree employs a prototype filter with half-band functions for channel center frequencies f.sub.l =l.multidot.B+B/2, with a real frequency multiplex input signal being separated into L.sub..nu. complex channel signals for further processing by means of a discrete Fourier transformation. For all stages M.sub..nu. =2 and L.sub..nu. =4 are fixed, with only two signals of the L.sub..nu. =4 being utilized. The arrangement permits adaptation of a hierarchical multi-stage method also to numbers of channels which are not equal to a power of two without changing the input sampling frequency and without the causing channels, whose number is fixed by the difference from the next higher power of two, to idle.

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First Claim