说明：  FIR滤波器， 设计一个线性相位有限冲激响应低通滤波器，使其满足如下指标：通带边界为2kHz，阻带边界为2.5kHz，通带波纹 =0.005，阻带波纹 =0.005，抽样率为10kHz。采用多尔夫-切比雪夫窗进行设计，进行频谱分析。
(FIR filter, design a linear phase FIR low-pass filter to meet the following indicators: passband border to 2kHz, stopband border to 2.5kHz, passband ripple = 0.005, stop-band ripple = 0.005, sampling rate of 10kHz. Used Dorf- Chebyshev window design, spectral analysis.)