Adaptive line enhancer and method of performing adaptive line enhancement

摘要

An improved adaptive line enhancer includes an adaptive Gray-Markel lattice notch filter having an adaptive notch frequency, in which the notch frequency is determined according to a notch frequency variable k. The value of k for the n+1SUPth /SUPsample period is determined according to the following equation: ?in-line-formulae description="In-line Formulae" end="lead"?k(n+1)=k(n)-sgn[y(n)]sgn[UPDATEFN]xmu?in-line-formulae description="In-line Formulae" end="tail"? in which y(n) is the notch filter output, mu is the adaptation constant, and UPDATEFN has a transfer function in the z-transform domain of: maths id="MATH-US-00001" num="00001" MATH OVERFLOW="SCROLL" MFRAC MROW MROW MO(/MO MROW MIalpha/MI MO-/MO MN1/MN /MROW MO)/MO /MROW MO⁢/MO MROW MO(/MO MROW MROW MIk/MI MO⁡/MO MROW MO(/MO MIn/MI MO)/MO /MROW /MROW MO-/MO MN1/MN /MROW MO)/MO /MROW MO⁢/MO MSUP MIz/MI MROW MO-/MO MN1/MN /MROW /MSUP /MROW MROW MN1/MN MO+/MO MROW MROW MIk/MI MO⁡/MO MROW MO(/MO MIn/MI MO)/MO /MROW /MROW MO⁢/MO MROW MO(/MO MROW MN1/MN MO+/MO MIalpha/MI /MROW MO)/MO /MROW MO⁢/MO MSUP MIz/MI MROW MO-/MO MN1/MN /MROW /MSUP /MROW MO+/MO MROW MIalpha/MI MO⁢/MO MSTYLE MTEXT /MTEXT /MSTYLE MO⁢/MO MSUP MIz/MI MROW MO-/MO MN2/MN /MROW /MSUP /MROW /MROW /MFRAC /MATH /MATHS in which alpha determines the bandwidth and k(n) is a variable for determining the current notch frequency. The algorithm for adapting the notch frequency enables the notch frequency to be directly calculated from knowledge of internal variables of the wave digital filter.