中文说明：
利用matlab工具箱函数，分别画出长度为15的矩形窗、汉宁窗、汉明窗和布莱克曼窗的幅频（dB）特性曲线，观察它们的主要参数（主瓣宽度、过渡带宽度、旁瓣峰值幅度）的差别。
English Description：
Using Matlab toolbox function, the amplitude frequency (DB) characteristic curves of rectangular window, Hanning window, Hamming window and Blackman window with length of 15 are drawn respectively, and the differences of their main parameters (main lobe width, transition band width, side lobe peak amplitude) are observed.