Index | Features | Expressions |
---|---|---|
Statistical | Root mean square | \(\sqrt {\frac{1}{n}\sum\nolimits_{i = 1}^{n} {x_{i}^{2} } }\) |
Variance | \(\frac{1}{n}\sum\nolimits_{i = 1}^{n} {\left( {x_{i} - \overline{x}} \right)^{2} }\) | |
Maximum | \(\max \left( x \right)\) | |
Skewness | \(E\left[ {\left( {\frac{x - \mu }{\sigma }} \right)^{3} } \right]\) | |
Kurtosis | \(E\left[ {\left( {\frac{x - \mu }{\sigma }} \right)^{4} } \right]\) | |
Peak-to-peak | \(\max \left( x \right) - \min \left( x \right)\) | |
Frequency | Spectral Skewness | \(\sum\nolimits_{i = 1} {k\left( {\frac{{f_{i} - \overline{f}}}{\sigma }} \right)^{3} S\left( {f_{i} } \right)}\) |
Spectral Kurtosis | \(\sum\nolimits_{i = 1} {k\left( {\frac{{f_{i} - \overline{f}}}{\sigma }} \right)^{4} S\left( {f_{i} } \right)}\) | |
Spectral power | \(\sum\nolimits_{i = 1}^{k} {\left( {f_{i} } \right)^{3} S\left( {f_{i} } \right)}\) | |
Time-frequency | Wavelet energy | \(\sum\nolimits_{i = 1}^{N} \omega t_{\phi }^{2} \left( i \right)/N\) |