说明：  利用firpmord和firpm函数设计双带通滤波器，其指标为，第一带通指标：f =4kHz,f =5 kHz ,f =3.6 kHz ,f =5.4 kHz 第二带通指标：f =6kHz,f =7 kHz ,f =5.6 kHz ,f =7.4 kHz 通带衰耗A <3dB，阻带衰耗A >40dB，抽样频率f =20kHz。
(Double belt pass filter using firpmord and firpm function design, for its indicators, through the first area index: f = 4 kHz, f = 5 kHz, f = 3.6 kHz, f = 5.4 kHz The second bandpass indicators: f = 6 kHz, f = 7 kHz, f = 5.6 kHz, f = 7.4 kHz Pass band attenuation A < 3 db, stop-band attenuation A > 40 db, f = 20 KHZ sampling frequency.)