Frequency-domain digital filtering techniques for the removal of powerline noise with application to the electrocardiogram.

This paper presents two new local processing frequency-domain methods for the removal of powerline noise from electrophysiological signals. The first is based on an iterative division or a multiplication of a set of frequencies centered at 60 Hz. The second users a basic property of the natural logarithm to smooth the 60-Hz noise. Both methods are intended to reduce powerline noise without affecting the frequency spectrum of the signal in the regions surrounding 60 Hz. For illustration, these local processing methods are applied to artificial and real electrocardiographic (ECG) data and are compared to a fixed IIR notch digital filter which is designed by pole-zero placements on the unit circle. The performance of each method is measured by the error squared, which is the square of the difference between the original noise-free signal and the filtered noisy ECG. Finally, since the two methods are iterative processes, comparison of their rate of convergence to a predefined noise reduction level is considered.