Table 4.

Summary of features for pre-processing [77].

Group	Method
Time domain	Mean, median, standard deviation, variance, minimum, maximum, range, root mean square (RMS), correction, cross-correlation, entropy, and kurtosis, skewness, peak to peak, crest factor [56], difference, zero crossing, integration, mean absolute deviation (MAD) etc.
Frequency domain	Fourier transform (FT), coefficients sum, dominant frequency, spectral energy, peak frequency, information entropy, entropy spectrum, spectral analysis of key coefficients, frequency range power (FRP) [13], etc.