Method for adaptive removal of distortion from binary coded digital

Abstract

Digital color television signals intended to be recorded in serial bit form are first subjected to predistortion to compensate for nonlinear distortion digitally computed for each serial bit on the basis of the pattern established by a predetermined number of precursor bits, which requires digital to analog conversion of the multibit parallel output of the predistortion computation. The converted output is then filtered on an analog basis to compensate for linear distortion, as by emphasizing the higher frequencies. In reproduction, the similar combination of analog and digital distortion compensation is used, first filtering and then, after retrieving the bit clocking frequency and phase, analog to digital conversion and compensation for nonlinear distortion by programmed interpretation of a parallel multibit input to select correctly the bits of an output serial bit stream. The latter can be subjected to conversion into the usual eight bit parallel color television signals. The combination of both programmed digital distortion compensation and analog compensation of linear distortion not only reduces the output bit error rate, but has the advantages of being adaptive in that a test bit sequence can be used to select the most effective program for correcting nonlinear distortion for a particular system of recording channel, record medium and reproduction channel, provided that the nonlinear distortion compensators use RAMs, so that the best variety of nonlinear distortion correction for a particular equipment and/or tape can quickly be selected.