On approximating an FIR filter using discrete orthonormal exponentials
David H. Friedman · IEEE Transactions on Acoustics Speech and Signal Processing · 1981
A given causal FIR filter may be approximated by an IIR filter of lower order requiring fewer memory elements. An iterative procedure is given for optimizing the approximation in the discrete time domain, based on representing the IIR function as a sum of orthonormalized complex decaying exponentials.