中文说明：用db小波对信号进行分解，并用小波系数进行信号的重构，对重构的信号进行傅里叶变化，进而分析各层小波系数重构的信号的频域特性。
English Description：
DB wavelet is used to decompose the signal, and wavelet coefficients are used to reconstruct the signal. Fourier transform is used to reconstruct the signal, and then the frequency domain characteristics of the reconstructed signal are analyzed.