1. A preprocessor for spectral pattern classification systems comprising a plurality of channel bandpass filter stages, the frequency response of the k-th frequency stage being substantially defined by ##EQU19## where K=0, .alpha., 2.alpha., 3.alpha.,. .. , [4]r.alpha. where N is the number of samples of data being filtered, r+1 is the number of stages, and .alpha. is an appropriately chosen positive integer constant typically selected to be =1, 2, 3, or 4.