RECIPROCAL INDEX LOOKUP FOR BTSC COMPATIBLE COEFFICIENTS

摘要

An algorithm calculates spectral expansion filter coefficients (712) using a value proportional to a reciprocal (720) of a feedback/feedforward signal (a ) and stores the coefficients to a lookup table. The lookup table is indexed b y a pre-selected set of coefficient bits to generate a filter coefficient function. A first portion of the lookup table stores a plurality of discrete values at index points of a line segment corresponding to a filter coefficie nt function approximation, so as to generate an initial discrete value corresponding to the filter coefficient function at a value of the high orde r bits and a second portion stores a plurality of slope values, which indicate s a slope of the filter coefficient function. A linear circuit interpolates/decimates an approximation of the compression/expansion filter coefficient function based on the slope value, the initial discrete value an d a preselected set of low order bits of the reciprocal value.