Recent advances in the design of selective linear-phase IIR digital filters

Design techniques are presented for infinite impulse response (IIR) digital filters with simultaneous conditions on amplitude and decay. Two classes of filter transfer functions are delivered. The first has maximally flat passband characteristics in both the amplitude and the group delay while possessing a Chebyshev-like stopband amplitude. The second class retains the same stopband behavior as the first, but the passband amplitude and delay approximate constancy in an interpolatory manner