Btsc encoder

Abstract

The disclosed BTSC encoder includes a left high pass filter means; 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 implementation of an analog adaptive signal weighting system for use with a digitally represented difference signal representing the difference between two stereophonic audio signals, the system including a signal path for transmitting an electrical information signal containing information relating to the difference signal of a predetermined bandwidth through the system, the analog adaptive weighting system being of the type including first analog control signal generator including a first analog filter component and a second analog control signal generator including a second analog filter component, the digital implementation further comprising:
 a digital filter arrangement disposed in the signal path and constructed and arranged so as to vary the gain impressed on the portion of the information signal within a first select spectral region within the predetermined bandwidth by a first variable gain factor, the first variable gain factor varying in response to and as a function of a first control signal;   a first digital control signal generator constructed and arranged so as to digitally generate the first control signal only in response to and in accordance with the signal energy of the digitally represented difference signal within a second select spectral region including at least a part of the first select spectral region, the first digital control signal generator including a first digital filter component having an amplitude response such that the difference between the amplitude response of the first digital filter component and the amplitude response of the first analog filter component is minimized irrespective of their respective phase responses;   a digital gain controller, disposed in the signal path and coupled to the digital filter arrangement, and constructed and arranged so as to vary the signal gain impressed on the information signal substantially throughout the predetermined bandwidth by a second variable gain factor, the second variable gain factor varying in response to and as a function of a second control signal;   a second digital control signal generator constructed and arranged so as to digitally generate the second control signal in response to and as a function of the signal energy of the digitally represented difference signal substantially within a third select spectral region within the predetermined bandwidth, the second digital control signal generator including a second digital filter component having an amplitude response such that the difference between the amplitude response of the second digital filter component and the amplitude response of the second analog filter component is minimized irrespective of their respective phase responses; and   wherein the digital filter arrangement, first control signal generator, digital gain controller, and the second control signal generator provide a frequency response in the digital domain that is substantially equal to the corresponding analog frequency response specified by the BTSC standard.   
     
     
         2 . A digital implementation according to  claim 1 , wherein the first digital filter component comprises a spectral bandpass filter. 
     
     
         3 . A digital implementation according to  claim 1 , wherein the first digital filter component comprises an IIR filter. 
     
     
         4 . A digital implementation according to  claim 1 , wherein the first digital filter component comprises a cascade of IIR filters. 
     
     
         5 . A digital implementation according to  claim 1 , wherein the second digital filter component comprises an IIR filter. 
     
     
         6 . A digital adaptive signal weighting system which accepts one or more digital input signals and modifies their electrical characteristics according to the BTSC standard to produce one or more digital output signals and to provide a frequency response in the digital domain that is substantially equal to the corresponding analog frequency response specified by the BTSC standard. 
     
     
         7 . A digital adaptive signal weighting system according to  claim 6 , wherein the input signal is a composite signal comprising one or more digital audio signals. 
     
     
         8 . A digital adaptive signal weighting system according to  claim 6 , wherein the output signal is a composite signal comprising one or more digital audio signals. 
     
     
         9 . A digital adaptive signal weighting system for use with a digital difference signal representing the difference between two stereophonic audio signals, comprising:
 a first digital filter section configured to alter the gain and phase of the digital difference signal within a first select spectral region according to the BTSC standard; and   a second digital filter section configured to further alter the gain and phase of the digital difference signal within a second select spectral region including at least a part of the first select spectral region according to the BTSC standard;   wherein the first and second digital filter sections provide a frequency response in the digital domain that is substantially equal to the corresponding analog frequency response specified by the BTSC standard.