The coefficient set for a bi-quad that makes a signalling flat filter. Some signalling tone schemes require such a filter, and some don't. It is termed a flat filter, to distinguish it from the sharp filter, but obviously it is not actually flat. It is a broad band weighting filter
Viterbi trellis state table 16 4D symbols deep, with 16 states each Each state has 4 entries: cumulative path metric, and prev. path pointer, x, y circularly addressed