Patent ID: 8908872

Claim:
A system for producing a digital composite modulated BTSC signal compliant with the BTSC standard, the system comprising: (A) a digital BTSC encoder operative to generate digital sum and difference signal components that are BTSC-compliant, wherein the digital BTSC encoder includes, (i) a sum channel processing section operative to process a digital sum signal and produce a digital conditioned sum signal according to the BTSC standard; and (ii) a difference channel processing section including a compression unit with a gain control feedback line, the difference channel processing section operative to encode a digital difference signal and produce a digital encoded difference signal according to the BTSC standard, wherein the digital difference signal represents the difference between left (L) and right (R) audio signals in left and right channels, respectively, wherein the difference channel processing section comprises a clipper; (iii) a lowpass filter operative to receive the digital difference signal and to produce an attenuation of signal energy above 15 kHz in the digital difference signal, and wherein the attenuation reduces instability in the gain control feedback line and the digital encoded difference signal, for avoiding audible artifacts and/or improving left (L) and right (R) channel separation upon decoding of the digital composite modulated BTSC encoded signal, and wherein the lowpass filter comprises first and second sections disposed in the difference channel processing section, and wherein the first section of the lowpass filter is disposed in the difference channel processing section before the compression unit and the clipper, and wherein the second section of the lowpass filter is disposed in the difference channel processing section after the compression unit and the clipper and before the feedback line of the compression unit; wherein the digital BTSC encoder has a digital domain magnitude response and digital domain inter-channel phase difference that are substantially equal to the analog domain magnitude response specified by the BTSC standard and analog domain inter-channel phase difference specified by the BTSC standard, respectively; and (B) a digital composite modulator operative to receive the digital encoded difference signal and the digital conditioned sum signal and to produce the digital composite modulated BTSC signal.