Line interference cancellation from corrupted EEG signals using modified linear phase FIR digital filters

One of the main disturbances in EEG signals is the 50 Hz line frequency signals. Here, the authors propose the use of a linear phase FIR digital low pass filter with finite wordlength precision coefficients, designed using the compensation procedure, to minimize 50 Hz interference signals from contaminated EEG signals. To make the filtering more effective, the authors use different structures, viz. cascading, twicing and sharpening (apart from simple low pass filtering) of the designed FIR filter. Modifications are proposed to twicing and sharpening structures to regain the linear phase characteristics which was lost in the conventional twicing and sharpening operations. The efficacy of all these transformed filters in minimizing 50 Hz interference signal has been studied using SNR improvement as performance measure for simulated signals. Time plots of the signals were also compared. Studies show that the modified sharpening structure is superior in performance compared to all other proposed methods. These algorithms have also been applied to real or recorded 50 Hz line frequency contaminated EEG signals. Comparison of time plots as also the output SNR show that the proposed modified sharpened structure works better in minimizing the artefacts compared to other methods considered.