The most effective way to verify the quality of an EMG signal is to first establish the noise baseline of the system.  Delsys EMG systems exhibit 5uV pk-pk noise baseline with the sensor inputs connected to Reference.  Once affixed to the skin, the noise baseline is between 5 and 10 uV pk-pk, depending on the impedance characteristics of the skin. This low baseline is observable only when the skin has been carefully cleaned and the muscle is completely relaxed.  A soon as the muscle fibers underneath the EMG sensor become activated, individual action potentials can be discerned, appearing at amplitudes as low as 20uV and as high as 2mV.  By maintaining a constant contraction level, an estimate of the EMG signal amplitude can be obtained.  A signal-to-noise ratio can be computed by calculating the Root-Mean Square (RMS) of the detected signal and dividing it by the RMS noise baseline of the system.  The formal signal-to-noise measurement is expressed in decibels, and is calculated as the logarithmic ratio of the RMS signal amplitude to the RMS noise amplitude.  The full scale signal-to-noise ratio of our EMG equipment is calculated as follows:

  • SNR = 20log(10mV/5uV)
  • SNR = 65dB