I'm new DSP fields, and slowly study of FIR Filer and with Matlab which is fir1 function.
My question is that
What do high and low order have a meaning in fir1 filter? I can't understand what does it have a meaning when N=2 or N=48.
In cut-off frequency, I found some explanation from the MATLAB as the below,
fir1 FIR filter design using the window method. B = fir1(N,Wn) designs an N'th order lowpass FIR digital filter and returns the filter coefficients in length N+1 vector B. The cut-off frequency Wn must be between 0 < Wn < 1.0, with 1.0 corresponding to half the sample rate. The filter B is real and has linear phase. The normalized gain of the filter at Wn is -6 dB.
B = fir1(N,Wn,'high') designs an N'th order highpass filter. You can also use B = fir1(N,Wn,'low') to design a lowpass filter. If Wn is a two-element vector, Wn = [W1 W2], fir1 returns an order N bandpass filter with passband W1 < W < W2. You can also specify B = fir1(N,Wn,'bandpass'). If Wn = [W1 W2], B = fir1(N,Wn,'stop') will design a bandstop filter.
But I want to know should we have to know the sample rate to set cut-off frequency? usually in practically, How does it handle to set the cut-off frequency?
- I've seen from the book, in the Liner system, if we put the impulse to the Liner system then we can totally analyze the system. In practically, how to implement the impulse signal to the liner system to get the filter information?