The SNR is the amplitude of the EMG signal recorded during muscle contraction relative to the electrical noise recorded when the muscle is not contracting. The SNR depends on the strength of the contraction and the quality of skin preparation, among other factors.
The higher the SNR, the more reliable the discrimination of EMG data from the underlying noise.
LOW BASELINE NOISE
The baseline noise represents the amplitude of the electrical signal that is recorded when the muscle is not contracting. It reflects the stability of the skin-electrode interface.
The lower the baseline noise, the higher the quality of the EMG signal.
NO LINE INTERFERENCE
The line interference is the electrical noise from power lines (50 or 60 Hz) and electrical devices that is present in almost all environments and that may contaminate the recording of EMG signals.
Line interference in EMG signals should be kept at a minimum level.
Clipping occurs when the amplitude of the sEMG signal goes beyond the range that can be reliably recorded by the sensor technology. It may occur if the signal amplification is excessive or if the recording sensor is not properly attached to the skin.
No clipping should occur in the EMG signal.
Use the Signal Quality Monitor to:
The best location of the sensor on the muscle for high amplitude EMG signal
Whether skin preparation is adequate for recording good quality EMG signals
The quality of the recorded EMG signals throughout the duration of your experiment
The quality of your EMG data
How do you achieve high-quality sEMG signals?
The Signal Quality Monitor provides guidance and suggestions to improve the quality of your sEMG signals.
The best location of the sensor is generally on the muscle belly, far from tendon origins and innervation zones.
The sensor should be aligned along the direction of the muscle fibers, which typically run longitudinally in a muscle.
For routine applications, the skin surface should be wiped with an alcohol swab to remove oil and debris. For more extreme conditions, such as in case of dry skin, repeatedly apply and peel hypo-allergenic tape to the skin sensor site to remove the outer layer of dead skin.
Firmly apply the sensor to the skin to ensure no movement occurs between the sensor contacts and the skin.
If your EMG signal contains excessive line interference, check your environment for electrical devices that could introduce noise in your recording. Stay as far as possible from external noise sources.