Table 3.
Sources of noise in the EMG signal.
| Noise source | Frequency range | Noise reduction |
|---|---|---|
| Cable motion artifact | 1–50 Hz | Ensure good contact between the electrode and skin. Use of short cables from the electrodes to the amplifier and securing these cables to minimize movement during the experiment. Use of the following electrode types: Ag-AgCl electrodes, wireless electrodes, and active electrodesa (72). pavee High-pass filtering with a cut-off frequency between 10 and 20 Hz |
| Electrode motion artifact | <20 Hz | Minimize the electrode–skin impedance with appropriate skin preparation (i.e., skin abrasion) (73, 74) pavee High-pass filter the EMG signal with a cut-off frequency between 10 and 20 Hz [though higher cut-off frequencies may be more appropriate to filter sEMG recorded during dynamic movements (75)] |
| Electrode-skin Interface | <8 Hz, >1,000 Hz | Minimize the electrode–skin impedance. Choose a signal amplifier with a high input impedance |
| Power line interference | 50 Hz in Europe and 60 Hz in North America and their harmonics (i.e., 100, 150, 200 Hz. etc., and 120, 180, 240 Hz, etc.) | Shield the EMG recording apparatus move it away from electrical equipment and power lines. Remove unnecessary electrical equipment nearby pavee Magnetically induced power line interference can be reduced by keeping the electrode leads short and/or by twisting the leads together, such that the loop area enclosed by the electrode leads, subject and signal amplifier is minimized pavee Experiments may be conducted within a Faraday cage, where available, to minimize electromagnetic interference |
| Electronic instrumentation | Typically, 10–500 Hz | Use of state-of-the-art recording systems |
| Quantization noise | Frequency independent (white noise) | Data acquisition system with sufficient A/D resolution [12-bit A/D convertor is typically regarded as the minimum acceptable for sEMG, with 16-bit or 32-bit A/D convertors preferred (76)] |
| Electrophysiological sources of noise (e.g., ECG artifact) | Typically, 0.1–100 Hz | Application of adaptive filtering in post-processing stage |
a
An active electrode processes the EMG signal (filters and amplifies) within the electrode itself.