Table 2 Frequency domain feature extraction method.

FFT

\({f}_{j}= \sum_{k=0}^{n-1}{x}_{k}{e}^{-\frac{2\pi i}{n}jk}\)

STFT

\(\mathrm{\rm X}\left(\mathcal{R},\upomega \right)= {\int }_{-\infty }^{\infty }x\left(\mathcalligra{t}\right)\mathcalligra{w}\left(\mathcalligra{t}-\mathcal{R}\right){\mathcalligra{e}}^{-jwt}dt=s\)

CWT

\({X}_{CWT}= \frac{1}{\sqrt{a}}{\int }_{-\infty }^{\infty }x\left(t\right)\psi \left(\frac{t-b}{a}\right)dt\)

CQT

\({X}_{CQT}\left(k, l\right)= \frac{1}{{N}_{K}}\sum_{n=0}^{{N}_{k}-1}\omega \left(n,k\right)x\left(n+lM\right){e}^{-\frac{j2\pi Qn}{N}}\)