The disclosed BTSC encoder includes a left high pass filter means for receiving a digital left channel audio signal and for digitally high pass filtering the digital left channel audio signal and thereby generating a digital left filtered signal; a right high pass filter means for receiving a digital right channel audio signal and for digitally high pass filtering the digital right channel audio signal and thereby generating a digital right filtered signal; a matrix means for receiving the digital left and digital right filtered signals, and including means for summing the digital left and digital right filtered signals and thereby generating a digital sum signal, and including means for subtracting one of the digital left and digital right filtered signals from the other of the digital left and digital right filtered signals and thereby generating a digital difference signal; a difference channel processing means for digitally processing the digital difference signal; and a sum channel processing means for digitally processing the digital sum signal.
1. A digital filter arrangement for processing digital audio signals according to the BTSC standard, the filter arrangement comprising:
a first digital filter configured to be disposed in the sum channel signal path of a digital adaptive signal weighting system, the digital filter configured for operation according to the BTSC standard, said filter having a passband that includes a substantial portion of the frequency range from 50 Hz to 15 kHz, and having a null or notch characteristic configured to pass relatively little signal energy at 15.734 kHz compared to nearby frequencies; and
a second digital filter configured to be disposed in the difference channel signal path of the digital adaptive signal weighting system, the second digital filter configured to produce an encoded digital difference signal as an output and including a wideband compression unit and a spectral compression unit configured on a feedback path, wherein the wideband compression unit includes a digital wideband bandpass filter configured to receive the encoded difference signal, a digital RMS level detector, and a digital reciprocal generator, and is configured to provide wideband compression in the difference signal, wherein the spectral compression unit includes a digital spectral bandpass filter configured to receive the encoded difference signal, a digital RMS level detector, and a variable emphasis unit with a digital variable emphasis filter and a logarithmic generator, and is configured to provide spectral compression in the difference signal;
wherein the second digital filter further includes a first dynamic phase equalization filter configured to accept a control signal from the logarithmic generator and introduce a desired compensatory phase error into the difference channel signal path to compensate for signal-dependent phase error between the response of the digital variable emphasis filter and that specified by the BTSC standard; and
wherein the first digital filter further includes a second dynamic phase equalization filter configured to accept a control signal from the logarithmic generator and introduce a desired compensatory phase error into the sum channel signal path to compensate for signal-dependent phase error between the response of the digital variable emphasis filter and that specified by the BTSC standard.
2. The digital filter arrangement of claim 1 , wherein said first filter is in the form of a lowpass filter with a passband that includes a substantial portion of the frequency range from DC to 15 kHz.