On-line estimation of myoelectric signal spectral parameters and nonstationarities detection

A method for detecting nonstationarities of random time series with an approximately Gaussian distribution of amplitudes is presented. This method is suitable for real time implementation. Some results obtained by applying them to a time series of spectral parameters of surface myoelectric signals are reported. The computerized system used to implement the detector of nonstationarity is described. This system realizes on-line estimation and display of spectral parameters, as well as detection of their nonstationarities, featuring a sampling frequency up to 20 k samples/s. A user friendly interface, fully menu driven, allows the user to select different options during the system´s operation by means of hot keys. The accuracy of the system was tested by comparing its estimates with those of an off-line system, previously characterized. The estimates of spectral parameters obtained by means of the two systems were always consistent. The on-line stationarity detector was able to recognize rates of variation of the spectral parameters as small as 1% during contractions lasting 10-15 s. This sensitivity makes it suitable for clinical application.