| 摘要 |
In a method of calculating a variable spectral compression filter coefficient in a BTSC compatible stereo encoder from a feedback variable, a reciprocal value that is proportional to a reciprocal of the feedback variable is calculated. A lookup table is indexed using a preselected set of bits of the reciprocal value to generate at least one parameter of the filter coefficient function. An approximation of the compression filter coefficient is linearly interpolated based on the at least one parameter of the filter coefficient function. An apparatus that includes circuitry that calculates a variable spectral compression filter coefficient in a BTSC compatible stereo encoder from a feedback variable includes a reciprocal value circuit that calculates a proportional to a reciprocal value of the feedback variable. The apparatus also includes a lookup table that is indexed by a preselected set of high order bits of the reciprocal value, wherein 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 wherein a second portion of the lookup table stores a plurality of slope values, each slope value indicating a slope of a line segment of the filter coefficient function, so as to generate a slope value of a line segment corresponding to the filter coefficient function at the value of the high order bits. A linear interpolation circuit interpolates an approximation of the compression filter coefficient based on the slope value, the initial discrete value and a preselected set of low order bits of the reciprocal value.
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