fir1 at 77 Frequencies must fall in range between 0 and 1. How to solve this problem? My program requires user to input filter order, cut off frequency. The sampling frequencies to be used are 8000 11025 22050 4410/

here's my program Fs = (get(handles.SAMPLING,'Value')); Fc1 = str2double(get(handles.CUTOFF,'String')); N = str2double(get(handles.Order,'String')); load voice z=fft(voice,512); w=(0:255)/256*(Fs/2); a=1; wn=Fc1/(Fs/2); b=fir1(N,wn); lowpassfilter=filter(b,a,voice); LOWfilter=fft(lowpassfilter,512); w=(0:255)/256*(Fs/2); axes(handles.axes1); plot(w,abs([LOWfilter(1:256)]));