采样数据过少，运用FFT变换不能分辨出其中的频率成分。添加零后可增加频谱中的数据个数，谱的密度增高了，但仍不能分辨其中的频率成分，即谱的分辨率没有提高。只有数据点数足够多时才能分辨其中的频率成分。-Sampling data is too small, the use of FFT transform can not distinguish the frequency components. Adding zero can increase the number of data in the spectrum, the density of the spectrum increased, but still can not distinguish the frequency components, that is, the resolution of the spectrum did not improve. Only the data points are enough to distinguish the frequency components.