Rejection of Power-Line Interference in EMG Signals Using a Notch Filter Initialized with Non-Zero States

This paper presents an improved method for rapid suppression of power-line interference (50 Hz) from electromyographic (EMG) signals. The proposed technique utilizes a digital notch filter initialized with carefully chosen non-zero initial conditions, combined with time-varying pole radius r(n) of the filter. Unlike classical solutions, which typically suffer from prolonged transient artifacts due to zero initialization and fixed filter parameters, the proposed approach achieves immediate interference attenuation by pre-setting the filter states as if the interference were already in steady-state. The performance of this approach was quantitatively assessed through experimental comparisons with a conventional fixed-radius notch filter and an adaptive LMS-based filter. Results demonstrate superior transient suppression, exhibiting lower mean square error (MSE) and minimal distortion of the useful EMG signal components. The proposed solution is particularly beneficial for biomedical signal processing applications where rapid settling and minimal signal distortion are critical, such as myoelectric prostheses and neurorehabilitation devices.