用matlab设计一个滤波范围在0到20HZ范围的滤波器

Fs = 80; % Sampling Frequency

Fpass = 20; % Passband Frequency
Fstop = 25; % Stopband Frequency
Dpass = 0.057501127785; % Passband Ripple
Dstop = 0.0001; % Stopband Attenuation
dens = 20; % Density Factor

% Calculate the order from the parameters using FIRPMORD.
[N， Fo， Ao， W] = firpmord([Fpass， Fstop]/(Fs/2)， [1 0]， [Dpass， Dstop]);

% Calculate the coefficients using the FIRPM function.
b = firpm(N， Fo， Ao， W， {dens});
Hd = dfilt.dffir(b);

freqz(Hd.Numerator，1，512);