Reply by Bernhard Holzmayer●March 17, 20042004-03-17
Abhishek Agrawal wrote:
> Hi,
>
> why Does MATLAB FIR1 function use -6 dB cutoff frequency instead
> of -3 dB ?
>
> I am using MATLAB 6.5 version.
>
> I am trying to design a LPF with the help of FIR1 function.
>
> n = 51; % order of the filter
> wn = 0.4 % cutoff frequency
> fir1(n,wn);
> freqz(b);
>
> Now my cutoff frequency should come on the -3 dB level but it is
> on -6 dB level.
"help fir1" tells at least that this is what you should expect.
"fdatool" reveals that this is a property of the algorithm they use
for calculation of windowed fir filter coefficients.
Maximally-flat fir filters instead provide -3dB at the wn-location.
Did you consider posting this question to the comp.soft-sys.matlab
ng?
Bernhard
>
>
>
> Regards
> Abhishek
Reply by Abhishek Agrawal●March 17, 20042004-03-17
Hi,
why Does MATLAB FIR1 function use -6 dB cutoff frequency instead of -3 dB ?
I am using MATLAB 6.5 version.
I am trying to design a LPF with the help of FIR1 function.
n = 51; % order of the filter
wn = 0.4 % cutoff frequency
fir1(n,wn);
freqz(b);
Now my cutoff frequency should come on the -3 dB level but it is on -6 dB level.
Regards
Abhishek