An improved method and means of determining reflection coefficients that characterize an electrical signal that obtains characteristics of an all-zero inverse lattice filter. The reflection coefficients are obtained by filtering the signal, sample the filtered signal, obtaining the elements of a correlation array from the samples, initializing values of arrays forward residuals, backward residuals, and cross correlation of residuals, combining array elements to obtain a first reflection coefficient, removing from the forward, backward and cross-correlation arrays the effect of the first reflection coefficient, calculating from the revised arrays a second coefficient, and repeating the calculations to the desired order. In a second embodiment of the present invention, samples are selected from the digitized signal and multiplied by a windowing function. The windowed samples are used to derive values of an autocorrelation array which eliminates the need for both forward and backward arrays as in the first embodiment of the invention.