an adjustable equalizer network has a series chain of n all pass amplifier stages driving n + 1 scaling circuits connected to a final summing circuit that includes circuitry to adjust the frequency response at m + 1 frequency control points to obtain a predetermined ripple free minimum phase shift frequency response over a given frequency range . the scaling circuits have scaling coefficients , of magnitude and sign determined by fourier analysis and an appropriate truncation function , such that the filter has a pass band representative of m + 1 contiguous bands conjointly encompassing the frequency range . calculation of the scaling coefficients and control of the scaling circuits is accomplished through digital computation and manipulation . some embodiments may use passive circuits or linear analogue circuits as scaling circuits , controlled manually or by a computing device .