Reciprocal index lookup for BTSC compatible coefficients
First Claim
1. A method for decoding an encoded BTSC composite audio signal comprising:
- digitally separating a L−
R signal and a L+R signal, both being encoded in the composite signal;
digitally applying deemphasis to the L+R signal;
digitally processing the L−
R signal, wherein the step of digitally processing includes computing spectral expansion coefficients and using said coefficients to spectrally expand the L−
R signal into a spectrally expanded output signal, wherein the coefficients for spectrally expanding the L−
R signal are determined based on a band-limited feed-forward compressed L−
R signal, and wherein a reciprocal of the RMS value of the feed-forward signal is used to determine the spectral expansion coefficients; and
combining the de-emphasized L+R signal with the digitally processed L−
R signal to produce separate I, and R audio signals.
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Accused Products
Abstract
An algorithm calculates spectral compression/expansion filter coefficients using a value proportional to a reciprocal of a feedback/feedforward signal and stores the coefficients to a lookup table. The lookup table is indexed by a pre selected set of coefficient bits to generate a filter coefficient function. A first portion of the lookup table stores a plurality of discrete values at index points of a line segment corresponding to a filter coefficient function approximation, so as to generate an initial discrete value corresponding to the filter coefficient function at a value of the high order bits and a second portion stores a plurality of slope values, which indicates a slope of the filter coefficient function. A linear circuit interpolates/decimates an approximation of the compression/expansion filter coefficient function based on the slope value, the initial discrete value and a preselected set of low order bits of the reciprocal value.
27 Citations
24 Claims
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1. A method for decoding an encoded BTSC composite audio signal comprising:
-
digitally separating a L−
R signal and a L+R signal, both being encoded in the composite signal;digitally applying deemphasis to the L+R signal; digitally processing the L−
R signal, wherein the step of digitally processing includes computing spectral expansion coefficients and using said coefficients to spectrally expand the L−
R signal into a spectrally expanded output signal, wherein the coefficients for spectrally expanding the L−
R signal are determined based on a band-limited feed-forward compressed L−
R signal, and wherein a reciprocal of the RMS value of the feed-forward signal is used to determine the spectral expansion coefficients; andcombining the de-emphasized L+R signal with the digitally processed L−
R signal to produce separate I, and R audio signals. - View Dependent Claims (2, 3)
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4. A method for decoding an encoded BTSC composite audio signal comprising:
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digitally separating a L−
R signal, a L+R signal and a SAP signal all being encoded in the composite signal;digitally applying deemphasis to the L+R signal; digitally processing the L−
R signal;digitally processing the SAP signal, wherein the step of digitally processing the SAP signal includes computing spectral expansion coefficients and using said coefficients to spectrally expand the SAP signal into a spectrally expanded output signal, wherein the coefficients for spectrally expanding 20 the SAP signal are determined based on a feedforward signal, which is based on a band-limited compressed L−
R signal, and wherein a reciprocal of the RMS value of the feed-forward signal is used to determine the spectral expansion coefficients; andcombining the de-emphasized L+R signal with the digitally processed L−
R signal to produce separate L and R audio signals. - View Dependent Claims (5, 6)
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7. A method for decoding a digital BTSC-compatible stereo television audio signal to generate a left and right audio output signal, the method comprising:
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digitally processing a feedforward portion of the digital BTSC signal at a predetermined sample rate using digitally modeled transfer functions to generate spectral expansion coefficients, the digitally modeled transfer functions being compliant with BTSC standard continuous time transfer functions, wherein the step of digitally processing is accomplished using bilinear transformation of analog transfer functions; using the spectral expansion coefficients to expand the digital BTSC signal; and using digital modeling techniques to model amplitude and phase characteristics of ideal analog decoder transfer functions. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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Specification