Patent ID: 7532728

Claim:
A BTSC signal encoder, comprising: a first low pass filter to receive and filter a digital left channel audio signal and a right channel audio signal, in which the first low pass filter operates as a higher order infinite impulse response (IIR) digital filter implemented using an allpass decomposition architecture; matrix means coupled to receive filtered left channel audio signal and right channel audio signal, sum the filtered left and right channel audio signals to generate a digital sum signal, and subtract one of the left or right channel audio signal from the other of the left or right channel audio signal to generate a digital difference signal; sum channel processing means coupled to process the digital sum signal; difference channel processing means coupled to process the digital difference signal, wherein the difference channel processing means includes a wideband amplifier and a spectral compressor, in which a gain for the wideband amplifier is set by a wideband gain feedback loop and a gain for the spectral compressor is set by a spectral gain feedback loop; and a second low pass filter to receive and filter an output of the difference channel processing means, in which the second low pass filter operates as a higher order IIR digital filter implemented using an allpass decomposition architecture and in which an output from the second low pass filter is coupled for processing with an output of the sum channel processing means and also coupled as feedback input to the wideband gain feedback loop and to the spectral gain feedback loop; wherein the first and second low pass filters, matrix means, sum channel processing means and the difference channel processing means operate at a sample rate to substantially match BTSC analog filter transform functions in both magnitude and phase.