US Patent 7623318 Noise reduction in same-gap servo in frequency-based servo tape systems

Noise in a same-gap, frequency-based servo tape system is reduced by applying correlated noise factors, generated during calibration, to filtered data write signals. The resulting noise values are subtracted from filtered servo signals, at frequencies F1 and F2, to generate first and second noise-compensated servo signals at frequencies F1 and F2. In one embodiment, the F1 and F2 data signals are filtered through two SOBP filters which output the magnitudes of the signals. The F1 and F2 servo signals are similarly filtered. In another embodiment, the F1 and F2 data signals are filtered through two Goertzel filters which output the real and imaginary components of the signals and the F1 and F2 servo signals are similarly filtered through two other Goertzel filters. Correlated noise factors are applied to the outputs of the write data Goertzel filters and the results subtracted from the corresponding outputs of the servo Goertzel filters.