做FFT只能看出信号在0到分析频率（采样频率的一半）之间的相对分布，或者说得到以采样频率归一化的频率。

采样频率即取样频率，指每秒钟取得信号样本的次数。所以，采样频率就是1/（delta t），其中delta t为连续采两次信号的时间间隔。

采样频率/采样点数=频率分辨率。

-Signal do FFT can only be seen in the 0 to the analysis frequency (half the sampling frequency) relative distribution, or get to the sampling frequency normalized frequency. Sampling frequency is the sampling frequency, refers to the number of times per second to obtain the signal samples. Therefore, the sampling frequency is 1/(delta t), which collected two consecutive delta t is the time interval signal. Sampling frequency/frequency resolution = sampling points.