System and method of performing digital multi-channel audio signal decoding

Abstract

A system and method are disclosed for performing digital multi-channel decoding of a BTSC composite audio signal. Each subsequent stage of the digital multi-channel decoding process is performed at the lowest sampling rate that yields acceptable performance for that stage. Analog-to-digital conversion of the composite audio signal is performed first to generate a composite digital audio signal. After analog-to-digital conversion, all signal processing may be performed in the digital domain. The composite digital audio signal is digitally filtered to frequency compensate for variations caused by previous stages of processing, including IF demodulation. Digital channel demodulation and filtering are performed to isolate single channels of the composite digital audio signal such as SAP, L−R, and L+R channels. SAP and L−R channels are DBX decoded resulting in corresponding decoded signals using a unique combination of digital filters that are an efficient translation of a corresponding combination of analog filters. The decoded L−R channel and the L+R channel are re-matrixed to form left and right stereo signals. Any of the SAP signal, left and right stereo signals, and L+R channel signal may be sample rate converted and output at a standard audio output rate.

1 - 21 . (canceled) 
     
     
         22 . A digital media decoder comprising:
 a fixed de-emphasis module operable to perform fixed de-emphasis on a media signal and to generate an intermediate signal;   a root mean square detector operable to receive the media signal and to generate a coefficient; and   a variable de-emphasis module operable to perform variable de-emphasis on the intermediate signal based on the coefficient.   
     
     
         23 . The digital media decoder of  claim 22 , wherein the coefficient generated by the root mean square detector is a function of signal frequency and magnitude. 
     
     
         24 . The digital media decoder of  claim 22 , wherein the variable de-emphasis module comprises an infinite impulse response (IIR) filter. 
     
     
         25 . The digital media decoder of  claim 22 , wherein the variable de-emphasis module comprises a look-up table that is addressed by the coefficient generated by the root mean square detector. 
     
     
         26 . The digital media decoder of  claim 25 , wherein the variable de-emphasis module further comprises an interpolation module operable to receive two nearest look-up table data values corresponding to the coefficient generated by the root mean square detector and operable to interpolate between the two nearest look-up table data values to generate an intermediate coefficient value. 
     
     
         27 . The digital media decoder of  claim 26 , wherein the variable de-emphasis module further comprises a coefficient generation module operable to receive the intermediate coefficient value generated by the interpolation module and to generate at least one final coefficient value based thereon. 
     
     
         28 . The digital media decoder of  claim 27 , wherein the variable de-emphasis module further comprises an infinite impulse response (IIR) filter operable to use the at least one final coefficient value in filtering the intermediate signal generated by the fixed de-emphasis module. 
     
     
         29 . The digital media decoder of  claim 22 , wherein the media signal comprises an audio signal. 
     
     
         30 . A method of performing variable de-emphasis on a communication signal, comprising:
 using an input coefficient to address a look-up table;   outputting two nearest look-up table data values corresponding to the input coefficient;   interpolating between the two nearest look-up table data values produced by the look-up table to produce a coefficient value; and   impulse response filtering an input signal based on the coefficient value produced by the interpolation.   
     
     
         31 . The method of  claim 31  wherein impulse response filtering the input signal comprises infinite impulse response filtering the input signal based on the coefficient value produced by the interpolation.