Use of finite wordlength FIR digital filter structures with improved magnitude and phase characteristics for reduction of muscle noise in EEG signals
One of the main disturbances in EEG signals is EMG artefacts generated by muscle movements. In the paper, the use of a linear phase FIR digital low-pass filter with finite wordlength precision coefficients is proposed, designed using the compensation procedure, to minimise EMG artefacts in contaminated EEG signals. To make the filtering more effective, different structures are used, i.e. 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 that are lost in conventional twicing and sharpening operations. The efficacy of all these transformed filters in minimising EMG artefacts is studied, using SNR improvements as a performance measure for simulated signals. Time plots of the signals are also compared. Studies show that the modified sharpening structure is superior in performance to all other proposed methods. These algorithms have also been applied to real or recorded EMG-contaminated EEG signal. Comparison of time plots, and also the output SNR, show that the proposed modified sharpened structure works better in minimising EMG artefacts compared with other methods considered.
KeywordsEEG EMG artefact FIR filters Filter structures Modified sharpening Phase characteristics
Unable to display preview. Download preview PDF.
- Chan, D. S. K. andRabiner, L. R. (1973): ‘Analysis of quantisation errors in the direct form for finite impulse response digital filters’,IEEE Trans.,AE-21, pp. 354–366.Google Scholar
- Johnson, T. L., Feidman, R., andSax, D. (1973): ‘Reduction of muscle artefact in electroencephalographic recordings’,Am. J. Electroenceph. Technol.,13, pp. 13–25.Google Scholar
- Johnson, T. L., Wright, S. C., andSegall, A. (1979): ‘Filtering of muscle artefact from the electroencephalogram’,IEEE Trans.,BME-26, pp. 556–563.Google Scholar
- McClellan, J. H., Parks, T. W., andRabiner, L. R. (1973): ‘A computer program for designing optimum FIR linear phase digital filters’,IEEE Trans.,AE-21, pp. 506–526.Google Scholar
- Narasimhan, S. V. andNarayana Dutt, D. (1985): ‘Software simulation of the EEG’,J. Biomed. Eng.,7, pp. 275–281.Google Scholar