说明：  1． 观察窗函数的影响。 信号为 ， KHz， KHz， KHz， 采样频率 KHz。 a) 写出 （ ）的频谱 ； b) 分别画出窗长度 ， ， ， 的矩形窗频谱和Hamming窗频谱。观察L的变化对窗谱的主瓣宽度、旁瓣密集度、相对旁瓣水平的影响。 c) 时域采样点数分别取 ， ， ， ， 分别画出 加矩形窗及加Hamming窗时DTFT频谱 ； 你能否从频谱上分辨出信号的三个频率分量？若能分辨出，它们的位置和相对大小是否准确？L的大小对频率的物理分辨率（physical frequency resolution）有何影响？
(1. To observe the effect of the window function. Signal, KHz, KHz, KHz, the sampling frequency KHz. a) write () spectrum b) Draw the window length, rectangular window spectrum and spectrum Hamming window. L to observe the changes in the spectrum of the main lobe of the window width, side lobe intensity, the relative impact of side lobe levels. c) time domain sampling points were taken,,,, respectively, plus the time to draw a rectangular window and add Hamming window DTFT spectrum Can you distinguish three frequency components of the signal from the spectrum? Distinguish if their location and relative size of the accuracy of? L impact on the physical size of the resolution frequency (physical frequency resolution)?)