用最少阶数设计一个数字滤波器，要求滤除频率在2000~2300Hz的信号，衰减比例不得小于40dB，1700Hz以下和2700Hz以上的信号要保留，最大衰减不能超过1dB，采样率为8000Hz。(The design of a digital filter with a minimum order requirements to filter the frequency in the 2000~2300Hz signal attenuation ratio shall not be less than 40dB, 1700Hz and 2700Hz above the signal to be retained, the maximum attenuation can not exceed 1dB, the sampling rate is 8000Hz.)