说明：  vb版本的fft变换，能够正反变换。正变换： 把时域信号转换成频域信号，反变换：能够把频域信号转换成时域信号。fft可广泛应用于工程领域，例如：信号的频域分析。震动，噪声的分析等等。
(vb version of the fft transform, to transform pros. Transformation : put time domain signal into frequency domain signal, anti-transformation : can frequency-domain signal into time domain signal. Fft can be widely used in engineering fields, such as : the frequency-domain analysis. Vibration, noise analysis, and so on.)