The surface electromyographic (sEMG) signal that originates in the muscle is inevitably
contaminated by various noise signals or artifacts that originate at the skin-electrode
interface, in the electronics that amplifies the signals, and in external sources.
Modern technology is substantially immune to some of these noises, but not to the
baseline noise and the movement artifact noise. These noise sources have frequency
spectra that contaminate the low-frequency part of the sEMG frequency spectrum. There
are many factors which must be taken into consideration when determining the appropriate
filter specifications to remove these artifacts; they include the muscle tested and
type of contraction, the sensor configuration, and specific noise source. The band-pass
determination is always a compromise between (a) reducing noise and artifact contamination,
and (b) preserving the desired information from the sEMG signal. This study was designed
to investigate the effects of mechanical perturbations and noise that are typically
encountered during sEMG recordings in clinical and related applications. The analysis
established the relationship between the attenuation rates of the movement artifact
and the sEMG signal as a function of the filter band pass. When this relationship
is combined with other considerations related to the informational content of the
signal, the signal distortion of filters, and the kinds of artifacts evaluated in
this study, a Butterworth filter with a corner frequency of 20 Hz and a slope of 12
dB/oct is recommended for general use. The results of this study are relevant to biomechanical
and clinical applications where the measurements of body dynamics and kinematics may
include artifact sources.
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